McQuay SuperMod IM-685-1 Manual

IM 685-1 1
Installation and Maintenance Manual IM-685-1
Group: Applied Systems
Part Number: IM685
Date: June 2001
SuperModTM Forced Draft Gas Fired Furnace
on McQuay Applied Rooftop Systems
HT***A* with RM7895A Flame Safeguard
© 2001 McQuay International

2 IM 685-1
General
Warranty Exclusion .......................................................... 3
Ventilation and Flue Pipe Requirements .......................... 3
Factory Mounting............................................................. 3
Factory Checkout ............................................................. 3
Installation
General ............................................................................. 3
Flue Box ........................................................................... 3
Wind Deflector ................................................................. 4
Electrical........................................................................... 4
Gas Pressure Requirements.............................................. 4
Gas Piping ........................................................................ 4
Valve and Regulator Venting............................................ 5
Normally Open Vent Valve .............................................. 6
Gas Piping Routing into Unit ........................................... 6
On-the-Roof Piping (Models 020-140) ........................ 6
Through-the-Curb Piping (Models 020-140)................ 6
Typical Piping Connections.......................................... 6
Gas Piping (Models 150-200)....................................... 7
Gas Piping Within the Vestibule................................... 7
Field Gas Piping Required............................................ 7
Condensate Drain.......................................................... 7
Vestibule (Models 150-200) ......................................... 7
Start-up & Operating Procedures
Start-up Responsibility..................................................... 8
Start-up Procedure............................................................ 8
Before Start-up ................................................................. 8
About This Burner............................................................ 8
Prepurge is Low-High-Low.......................................... 8
Low Fire Start............................................................... 8
"Pilot" is Main Flame Modulated Down
to Pilot Rate ................................................................ 8
Set Control System to Enable Heating............................. 8
Start-up Preliminary ......................................................... 8
Preliminary "Dry" Run..................................................... 9
Flame Start-up .................................................................. 9
Modulate Firing Rate ....................................................... 9
Combustion Tests ........................................................... 10
Cycle the Unit................................................................. 10
Record Data.................................................................... 10
References
Typical Electrical Schematic .......................................... 10
Typical Sequence of Operation ...................................... 10
Typical Piping Schematic................................................11
Typical Burner Control Box ........................................... 12
Flame Safeguard
Keyboard Display Module..............................................12
Operation.........................................................................12
Normal Start-up ..............................................................12
LED Display ...................................................................12
Service
General ............................................................................13
Gun Assembly.................................................................13
Gun Assembly Removal and Installation .......................13
Flame Rod Adjustment ...................................................13
Flame Rod Installation....................................................13
Ignition Electrode Adjustment........................................13
Air & Gas Adjustments...................................................14
Gas Supply Pressure .......................................................14
High Pressure Regulator .................................................14
Gas Adjustment...............................................................14
Air Adjustment................................................................14
Air and gas Control Linkage...........................................14
Actuator Crankarm..........................................................15
Switch Adjustments ........................................................15
Altitude Considerations ..................................................15
Gas Valve Pressure Regulator Adjustment .....................16
Adjustment Procedure for Parallel Valves ......................16
Check Manifold Pressure at Minimum rate ....................16
Combustion Testing ........................................................17
Verify Input Rate.............................................................17
Check CO2, CO and Stack Temperature .........................17
Cleaning Heat Exchanger (Models 032-200) .................17
Cleaning Heat Exchanger (Models 020-025) .................18
Leakage Symptoms.........................................................18
Checking for Leaks .........................................................18
Causes of Failures ...........................................................18
Replacing a Heat Exchanger...........................................19
Furnace Condensation ....................................................19
Rear Cleanout Port ..........................................................20
Furnace Condensate Drain Kit........................................20
Considerations .............................................................20
Install .875 Copper Drain Line....................................20
Install the Cover Over Drain Pipe ...............................20
Combination Fan and Limit Control...............................20
Maintenance
Monthly, Twice Yearly, Yearly........................................21
Troubleshooting Chart ....................................................22
Typical Parts List - 60 Hz ...............................................24
Capacities & Adjustments Table.......................... 25
Performance & Service History............................ 26
When writing to McQuay for service or replacement parts, refer to the model number of the unit as stamped on the serial plate,
attached to the unit. If there is an in-warranty failure, state the date of installation of the unit and the date of failure along with an
explanation of the malfunctions and the description of the replacement parts required. Parts are warranted for ninety (90) days
unless covered by original unit warranty.
SERVICED BY:
TELEPHONE NO: INSTALLATION DATE:
Installer: Leave this manual with owner. It is to be posted and maintained in legible condition.

IM 685-1 3
General
This forced draft gas burner is specifically designed for use
with the furnace on McQuay applied rooftop heating and air
conditioning units which are for outdoor installation only.
Each model size has unique burner head components to tai-
lor the shape of the flame to each particular stainless steel
combustion chamber, to match the capacity requirement, and
to offer a desirable turndown potential when arranged for
modulation. This is a forced draft burner with a high pres-
sure combustion air fan and will operate against pressure.
This eliminates the need for draft inducers, chimneys, draft
hoods, barometric dampers, and Breidert caps.
Warranty Exclusion
Warranty is void if furnace is operated in the presence of
chlorinated vapors, if the airflow through the furnace is not
in accordance with rating plate, or if the wiring or controls
have been modified or tampered with.
Ventilation & Flue Pipe Requirements
The McQuay applied rooftop unit is equipped with an out-
door air louver to supply adequate combustion air. The unit
also has a flue outlet assembly and requires no additional
chimney, flue pipe, Breidert cap, draft inducer, etc.
Factory Mounting
This burner and gas train has been installed and wired at the
factory. See "Gas Piping." Also note that models 150
through 200 have the burner removed for shipment; see
"Installation: Models 150-200."
Factory Checkout
This complete heating plant was fired and tested at the fac-
tory. It was adjusted to the required capacity and efficiency.
Modulating air and gas linkages, pressure regulators, and
stops were adjusted for proper operation at all firing levels.
The unit was fired through several complete start-up through
shutoff sequences to check operation. A check was made of
the air switch, gas pressure switch, high limit operation, and
combustion characteristics including C02and CO (at several
firing rates on modulating burners).
WARNING
Units equipped with gas heating must not be operated
in an atmosphere contaminated with chemicals which
will corrode the unit such as halogenated hydrocar-
bons, chlorine, cleaning solvents, refrigerants, swim-
ming pool exhaust, etc. Exposure to these compounds
may cause severe damage to the gas furnace and result
in improper or dangerous operation. Operation of the
gas furnace in such a contaminated atmosphere consti-
tutes product abuse and will void all warranty coverage
by the manufacturer. Questions regarding specific con-
taminants should be referred to your local gas utility.
If the burner was specified for operation at higher altitudes,
combustion air adjustments were compensated to result in
proper settings at the higher altitude. This checkout nor-
mally eliminates on-the-job start-up problems; however, the
equipment is subject to variable job conditions and shipping
shocks can change adjustments, cause damage, and loosen
connections and fasteners. Therefore, it is necessary to go
through the complete start-up procedure even though the
unit may appear to be operating properly.
Installation
General
The installation of this equipment shall be in accordance
with the regulations of authorities having jurisdiction and all
applicable codes. It is the responsibility of the installer to
determine and follow the applicable codes. Sheet metal
parts, self-tapping screws, clips, and such items inherently
have sharp edges, and it is necessary that the installer exer-
cise caution. This equipment is to be installed by an experi-
enced professional installation company that employs fully
trained technicians.
Flue Box
The flue box is not installed at the factory because it would
increase the width of the unit beyond the allowable shipping
width. All holes are prepunched, the fasteners are furnished
and everything is shipped inside the burner vestibule of the
unit. On Models 150 through 200 it is shipped in the same
crate as the vestibule. Remove and discard the shipping
cover installed over the furnace tube outlets before installing
the flue box.
1. Remove the screws (2) in the casing of the unit that line
up with the bottom lip holes of the flue box tube sheet
(3). These screws will later be replaced, at which time
they will also attach the bottom of the flue box to the
unit.
2. Install the flue box tube sheet (3), attaching top to roof
dam strip with screws (1). Do not attach bottom at this
time.
3. Apply a 1/8 to 3/16 inch bead of high temperature sili-
cone around each tube to seal it to the flue box tube sheet
(3) and prevent condensate from running back toward the
unit along the outside of the tube. See Figure 1. Also
apply a bead of high temperature silicone to seal both
sides to the bottom of the flue box wrapper (4), being
careful not to obstruct the square drain holes in each front
corner.
4. Install flue box wrapper sheet (4) by sliding it up from
below so as not to disturb the silicone seal described in
3 above. Attach with side screws (5). At this time rein-
stall bottom screws (2).

4 IM 685-1
Figure 2. Wind Deflector (Models 032 thru 140)
Electrical
The McQuay burner receives its electrical power from the
main unit control panel. No additional power wiring must be
routed to the burner. The sequencing of the burner is also
controlled through this panel and therefore is factory wired.
No additional wiring will be required. Note that models 150
through 200 furnaces require reassembly of some electrical
connections as the burner is removed for shipment.
Gas Pressure Requirements
The pressure furnished to the combination gas control(s)
must not exceed 13.9 in. W.C. When the supply pressure is
above 13.9 in. W.C. a high pressure regulator must precede
the combination gas control(s). The inlet gas pressure cannot
exceed the maximum pressure rating of the high pressure
regulator and the outlet pressure must be such that it will
furnish gas to the appliance pressure regulator within the
pressure range mentioned above, preferably at 7.0 in. W.C.
when firing at maximum rate.
Gas Piping
The connection size at the burner is shown in Table 5 under
Column 13 thru 15. Gas piping must be sized to provide the
minimum required pressure at the burner when the burner is
operating at maximum input. Consult the appropriate local
utility on any questions on gas pressure available, allowable
piping pressure drops, and local piping requirements.
Install all piping in accordance with the National Fuel Gas
Code (ANSI Z223.1), (NFPA 54-1999) and any applicable
local codes.
It is very important that the proper size piping be run from
the meter to the gas burner without reductions. Undersized
piping will result in inadequate pressure at the burner. The
pressure will be at its lowest when it is needed the most, at
times of maximum demand. Therefore, it can cause intermit-
tent hard-to-find problems because the problem may have
left before the service technician has arrived. Avoid the use
of bushings wherever possible.
WARNING
Improper installation, adjustment, alteration, service or
maintenance can cause property damage, injury or
death. Read the installation, operating and maintenance
instructions thoroughly before installing or servicing
this equipment.
FOR YOUR SAFETY
If you smell gas:
1. Open Windows
2. Don’t touch electrical switches.
3. Extinguish any open flame.
4. Immediately call your gas supplier.
FOR YOUR SAFETY
The use and storage of gasoline or other flammable
vapors and liquids in open containers in the vicinity of
this appliance is hazardous.
435
1
2
Drain Opening
(both corners)
Seal Side
Seams
Seal Around
Each Tube
Figure 1. Flue Box
Tube Ends
Flue Box
Wrap
Flue Box
Tube Sheet
Wind Deflector
Hinge Inner
Screw
Burner
Access
Door
4
3
Wind Deflector
The wind deflector is not installed at the factory because it
would increase the width of the unit beyond the allowable
shipping width. The deflector is shipped in the burner vesti-
bule of the unit. Install the wind deflector over the combus-
tion air intake opening of the burner compartment before
operating the burner. Use inner hinge screws on top hinged
door (see Figure 2). Side hinged doors have holes for mount-
ing (see Figure 5). Models 020 and 025 have a different style
wind deflector. It mounts on the door and has a top opening
flush with the roof of the unit (see Figure 14).

IM 685-1 5
Remove all burrs and obstructions from pipe. Do not bend
pipe; use elbows or other pipe fittings to properly locate
pipe. A drip leg must be installed in the vertical line before
each burner such that it will not freeze. Install unions so gas
train components can be removed for service. All pipe
threads must have a pipe dope which is resistant to the
action of LP gas. After installation, pressurize the piping as
required and test all joints for tightness with a rich soap
solution. Any bubbling is considered a leak and must be
eliminated. Do not use a match or flame to locate leaks.
Valve & Regulator Venting
Valve diaphragm vents, pressure regulator vents, and pres-
sure switch vents are located in the outdoor burner vestibule
and therefore vent tubing is not run to the outside of this ves-
tibule. If local regulations require that this be done, it is a
part of the field gas piping hookup. Remove any plastic pro-
tector plugs from regulator and valve vents.
Normally Open Vent Valve
Vent valves such as required by IRI for over 1000 MBH
input units must always be routed to the outdoors. This is
field piping.
Table 1. Capacity of pipe natural gas (CFH)
WITH PRESSURE DROP OF .3" W.C. & SPECIFIC GRAVITY OF 0.60
PIPE
LENGTH (FT.)
PIPE SIZE-INCHES (IPS)
½¾ 11¼1½22½3 4
10 132 278 520 1050 1600 2050 4800 8500 17500
20 92 190 350 730 1100 2100 3300 5900 12000
30 73 152 285 590 890 1650 2700 4700 9700
40 63 130 245 500 760 1450 2300 4100 8300
50 56 115 215 440 670 1270 2000 3600 7400
60 50 105 195 400 610 1150 1850 3250 6800
70 46 96 180 370 560 1050 1700 3000 6200
80 53 90 170 350 530 990 1600 2800 5800
90 40 84 160 320 490 930 1500 2600 5400
100 38 79 150 305 460 870 1400 2500 5100
125 34 72 130 275 410 780 1250 2200 4500
150 31 64 120 250 380 710 1130 2000 4100
175 28 59 110 225 350 650 1050 1850 3800
200 26 55 100 210 320 610 980 1700 3500
Note: Use multiplier below for other gravities and pressure drops.
Table 2. Specific gravity other than 0.60
SPECIFIC GRAVITY MULTIPLIER
0.50 1.100
0.60 1.000
0.70 0.936
0.80 0.867
0.90 0.816
1.00 0.775
Table 3. Pressure drop other than 0.3"
PRESSURE
DROP MULTIPLIER PRESSURE MULTIPLIER
0.1 0.577 1.0 1.83
0.2 0.815 2.0 2.58
0.3 1.000 3.0 3.16
0.4 1.16 4.0 3.65
0.6 1.42 6.0 4.47
0.8 1.64 8.0 5.15

6 IM 685-1
Gas Piping Routing Into Unit
On-The-Roof Piping (Models 020-140)
1. Remove knockout (1) at corner of burner vestibule door
and saw out corner of door. See Figure 3b. Make saw cuts
(2) tangent to round hole and square with door edges.
2. Install pipe corner plate (3) on vestibule, locating on pre-
punched holes. See Figure 3c. This part is shipped inside
the vestibule.
3. Route gas supply pipe through hole. Carefully plan pipe
route and fitting locations to avoid interference with
swinging of doors, etc.
Through-The-Curb Piping (Models 020-140)
1. Remove bottom access panel (5). See Figure 3c.
2. Remove knockout (4) and make an opening (6) through
bottom deck directly below knockout hole.
3. Route gas pipeline through these openings and seal them
off with suitable grommets (7).
See Figure 3a Section A-A.
4. Replace bottom access panel (5).
Typical Piping Connections
Figure 4.
A = Shutoff Cock (ball valve)
B = Union - Furnished.
C = Gas Pipe - Routed in through front
D = Gas Pipe - Routed in through curb
E = Factory Piped Gas Trains
2
1
7
7
4
6
A
A
See Figure 3c Gas Supply
Section A-A
3
45
2
Figure 3a.
Figure 3b.
Figure 3c.
C
C
DB
A
D
A
FSG
E
With Shutoff Cock
Folded Back
With Shutoff Cock
In Front
Figure 4b. Figure 4a.

IM 685-1 7
is accessible from outside the unit, that valve must be relocated
or an additional valve added. In locating such a valve, it is to
be readily accessible and located such that no obstructions
interfere with operation of the handle. See Figure 16a, "Valve
and Regulator Venting", and "Normally Open Vent Valves".
Condensate Drain
Models 020 and 025 are equipped with a 3/4" I.P. condensate
drain pipe projecting from the back side of the furnace section
(see Figure 14). If applicable codes or regulations requires this
can be trapped and/or routed to a drain. Also see "Furnace
Condensation" section.
Vestibule (Models 150 thru 200)
These two furnace sizes exceed the allowable shipping width
and for this reason the burner is disconnected and removed for
shipment. A sheet metal vestibule weather enclosure is also
disassembled for shipment. At installation the burner must be
re-mounted, the tagged electrical connections re-attached, and
the vestibule re-assembled and mounted as shown in Figure 5.
These items are packed in a crate and shipped as a separate
item.
Gas Piping (Models 150 thru 200)
The gas piping cannot be routed up to the burner from
within the curb on Models 150 through 200. Gas piping
must be routed across the roof to under the burner vesti-
bule, or a pitch pocket can be provided there. The installer
must cut a hole in the bottom panel of the overhanging
burner vestibule through which to route the gas line up to
the burner gas train. The bottom panel of the vestibule is
at approximately the same elevation as the top of the curb.
Gas Piping within the Vestibule
The gas piping layout within the vestibule will vary
according to the complexity and size of the gas train rela-
tive to the available room within the vestibule. As an
example, a gas train with a high pressure regulator and an
extra safety shutoff valve (when required for IRI, etc.) will
require careful use of the available space. The examples
shown in Figure 4 indicate typical piping layouts.
Field Gas Piping Required
The gas train components have all been factory installed
and require only a connection to the supply gas line. The
manual shutoff valve is located within the burner vesti-
bule. If local codes require a manual shutoff valve that is
Figure 5.
Cut Gas Line Opening
Hinge
Side Panel
Door
Top Panel
Side Panel,
With Latch
Bottom Panel
#10 Screw
Door
Fasten Wind Deflector
To Door With #10 Screws,
(Door & Wind Defletor
Part of Vestibule Kit)

8 IM 685-1
Start-up & Operating Procedures
Start-up Responsibility
The start-up organization is responsible for determining that
the furnace, as installed and as applied, will operate within
the limits specified on the furnace rating plate.
1. The furnace must not exceed the specified "Maximum
MBH Input." See "Verify Input Rate."
2. The furnace must not operate at an airflow below the
specified "Minimum Airflow CFM." On variable air vol-
ume systems it must be determined that the furnace will
not be operated if or when system cfm is reduced below
the specified minimum airflow cfm.
3. It must be established that the gas supply is within the
proper pressure range. See "Gas Pressure Requirements."
Start-up Procedure
Only qualified personnel should perform the start-up and
service of this equipment. It is highly recommended that the
initial start-up and future service be performed by McQuay
certified technicians who are familiar with the hazards of
working on live equipment. A representative of the owner or
the operator of the equipment should be present during start-
up to receive instructions in the operation, care and adjust-
ment of the unit.
Before Start-up
1. Notify any inspectors or representatives that may be
required to be present during start-up of gas fuel equip-
ment. These could include the gas utility company, city
gas inspectors, heating inspectors, etc.
2. Review the equipment and service literature and become
familiar with the location and purpose of the burner con-
trols. Determine where the gas and power can be turned
off at the unit, and upstream of the unit.
3. Verify that power is connected to the unit and available.
4. Verify that the gas piping, meter, and service regulator
has been installed, tested, and is ready to go.
5. Verify that proper instruments will be available for the
start-up. A proper start-up requires the following: voltme-
ter, manometer or gauges with ranges for both manifold
pressure and inlet gas pressure, keyboard display module
or a 20K ohm/volt meter for flame safeguard signal
strength measurement, CO2indicator, carbon monoxide
indicator, and a stopwatch for timing the gas meter.
About This Burner
Prepurge is Low-High-Low
The burner air control valve will be at the minimum position
during off cycles. Upon a call for heat or any other time that
a prepurge cycle occurs, the air control valve will be reposi-
tioned to the maximum position for the prepurge and then
returned to the minimum position for low fire start.
Low Fire Start
The burner is controlled for proven low fire start. The actua-
tor will position the modulating gas valve and the modulat-
ing air valve to the low fire position each time the burner is
to light off. Switch LS1 proves the air and gas valves are at
the low fire position. If LSl is not "made" at light off, the gas
valves cannot open and the flame safeguard will lock out,
requiring manual reset.
"Pilot" is Main Flame Modulated Down to Pilot Rate
The "pilot" is not a separate flame or burner. The "pilot" is
the main flame operating at its minimum rate. That mini-
mum rate is so low that it qualifies as a pilot burner.
Set Control System to Enable Heating
To allow start-up and check-out of the burner, the control
system must be set to call for heating and must he used to
control the amount of heating. Set the control system to call
for heat so MCB-B011 energizes Relay R20. With MCB-
B011 closed, vary the temperature control set point to
increase, maintain, or reduce the firing rate of the burner as
required for these tests. If MCB-B09 is closed the firing rate
will decrease. If MCB-B010 is closed the firing rate will
increase. If neither are "made" the firing rate will remain
unchanged.
Start-up Preliminary
1. Before energizing the burner verify that the modulating
air and gas valve mechanism moves freely and is not
binding, and check the linkage fasteners for tightness.
This can be accomplished without affecting any adjust-
ments. Remove shoulder screw (12), Figure 16a, that
connects the teflon bushing to the actuator crank arm.
The control rod can now be manually moved back and
forth, it should feel smooth with no binding or scraping.
Always remove shoulder screw (12) and test for binding
after reinstalling the gun assembly on Models HT050-
200.
2. Close the gas line cocks. Install a Keyboard Display
Module, Honeywell Part No. S7800A1001, or connect a
20K ohm/volt meter to the test jack on the flame safe-
guard (see Figure 7).
3. Check the burner fan wheel for binding, rubbing, or loose
set screws.
4. Check power. Position switch S3 on burner control panel
to AUTO. The LED marked POWER on the flame safe-
guard should come on and after a 10 second "Initiate"
period the burner motor should start. Check for (CW)
rotation as viewed through the burner fan housing inlet. If
the motor does not start, press the reset button on the
flame safeguard. If the motor still does not start, consult
the appropriate section of the "Troubleshooting Guide".
Continue on to Item 5 when burner motor will run 10 sec-
onds after the switch is positioned to AUTO.
WARNING
Should overheating occur or the gas supply fail to shut
off, turn off the manual gas valve to the appliance before
shutting off the electrical supply.

IM 685-1 9
5. Check voltage. With burner switch S3 at AUTO, measure
voltage across burner control box terminals 2 and NB. If
it is not between 114 and 126 volts, check the voltage and
tapping connections to the supplying transformer at the
unit main control panel.
6. Purge the gas lines. Turn off electrical power. Remove
the 1/8 inch pipe plug from the inlet pressure tap of the
first electric gas valve in the line, open the gas line cocks
upstream from there and bleed the gas line of all air.
Replace the1/8 inch pipe plug.
7. Leak check. Using a rich soap-water mixture and a brush,
check the gas lines for leaks. Correct all leaks before
starting burner. After the burner is operating and all the
downstream valves are open, leak check that portion of
the gas train.
8. Connect a manometer to measure gas manifold pressure
at (1), Figure 16a. There is a 1/8 inch pipe size plugged
tapping in the gas line just before it enters the burner
housing.
Preliminary "Dry" Run
1. Close the gas line cock, Remove the burner front cover
and open the control panel door. Switches LS1 and LS2
in the lower right hand corner of the control box should
be in view and the modulating actuator VM1 should be at
the minimum rate position. Verify that the right hand
switch LS1 is being held in the 'made' position by the col-
lar on the control rod and that the switch lever is not bot-
tomed out against the plastic switch housing.
2. Position the burner switch S3 to AUTO. The flame safe-
guard will go through a 10 second "Initiate" period, after
which the burner motor will start. The modulating gas
valve actuator VM1 will drive the air valve and gas valve
to the maximum rate position. Observe the linkage for
any binding, loose fasteners, or other problems that could
have resulted from shipping.
3. When the actuator reaches the maximum rate position,
verify that the left hand switch LS2 is held in the 'made'
position by the collar on the control rod and that the
switch lever is not bottomed out against the plastic switch
housing.
4. Position the burner switch S3 to OFF. Close the control
panel door and reinstall the burner front cover. Prepare to
measure the burner air box pressure by holding a rubber
manometer tube tightly over port ➃, Figure 16b. The
tube must surround the hole and seal tightly against the
burner housing to measure the static pressure through the
hole.
5. Position the burner switch S3 to AUTO and with the
burner actuator VM1 at the maximum rate position mea-
sure the burner air box pressure at port ➃, Figure 16b.
The actuator will remain at this position for the first 20
seconds of the prepurge period. Typical static pressure
readings are listed in Table 5, Column 6. Any appreciable
deviation from these values would indicate a burner air
problem that should be found before attempting to fire
the burner. These problems could include linkages dis-
turbed during shipment, etc.
Flame Start-up
1. Open the gas line cocks and position switch S3 to AUTO.
The flame safeguard will go through the 10 second "Ini-
tiate" period, after which the burner motor will start. The
modulating air and gas valve actuator VM1 will drive the
air valve to the full open position. At full open the 60 sec-
ond prepurge period will begin. After 20 seconds at maxi-
mum open, the actuator will begin a 30 second stroke to
reposition the air valve back to the minimum position.
Upon completion of the 60 second prepurge cycle, gas
valve GV1 will open (as indicated when the LED marked
PILOT comes on), the ignition transformer is powered
and the flame should come on at minimum rate.
2. Observe the gas manifold pressure manometer during this
sequence. The manifold pressure should be close to zero
(it will indicate a slight heat exchanger pressure caused
by the burner combustion air fan). When gas valve GV1
opens it should indicate a manifold pressure approximate
to the values listed in Table 5, Column 10. Approxi-
mately 3 seconds after GV1 is powered the flame will
come on and the flame signal will read 1.5 to 5.0 volts
DC. The LED marked FLAME will come on when flame
is detected and the LED marked MAIN will come on if
flame is being detected at the end of the 10 second trail
for ignition period. When the LED marked MAIN comes
on gas valves GV4-GV8 (when included) will also open
and the firing rate will be determined by the control sys-
tem. On the initial start-up if the flame does not light and
the flame safeguard locks out, reset it and make several
attempts to light before assuming there are problems
other than more air in the gas lines. If initial flame opera-
tion is erratic wait until after a period of main flame oper-
ation has further purged the gas lines before trying to
"adjust out" something that may actually be caused by air
in the lines.
Modulate Firing Rates
Set the temperature control system so the burner actuator
VM1 will modulate to increase the firing rate. Observe the
flame signal and the manifold pressure manometer as this is
occurring. The flame signal should remain between 1.5 to
5.0 volts DC through the entire range of the burner, and the
manifold pressure should be between the values indicated by
Table 5, Column 9 and 10. If the manifold pressure shoots
above these values and then slowly returns to normal as the
burner is modulating down to a lower firing rate, isolate
which combination gas control is causing this. Check that
valves pressure regulator adjustment per "Gas Valve Pres-
sure Regulator Adjustment" section. If this condition cannot
be adjusted out, replace the valve. If combustion appears
normal, proceed with the combustion test.

10 IM 685-1
Combustion Tests
These tests should be run when the furnace is at normal oper-
ating temperature (after the furnace has been running 10 to 15
minutes), and should be run at several firing rates including
maximum and minimum.
a. Check input: See Verify Input Rate
b. Check C02: See Check CO2, CO & Stack Temperature
c. Check CO: See Check CO2, CO & Stack Temperature
Cycle the Unit
Cycle the unit through several start-ups with the temperature
controls calling for first minimum rates and finally maxi-
mum rates. Be alert for any hints of trouble or unexplained
inconsistencies that could indicate future problems.
Record Data
After the gas burner has been successfully started up, checked
out and is operating correctly, readings should be taken and
recorded for future reference (see Table 6). If problems
develop in the future, variations in these readings will indi-
cate what has changed and where to start looking for prob
Figure 6a. Typical Electrical Schematic with RM7895A

IM 685-1 11
Typical Sequence of Operation
When the rooftop unit is energized 120 volt power is sup-
plied to the system on/off switch (S1), to burner on/off
switch (S3) and 24 volts to the (BO#11) contacts on the main
control board (MCB).
Note: On field supplied controls, 120V power is supplied
through the system on/off switch (S1) to burner on/off
switch (S3) and to the field supplied gas heat on/off
contacts.
Burner on/off switch (S3) will power the modulating gas
valve actuator (VM1) and terminal #5 (L1) on the flame
safeguard (FSG). Upon a call for heat, the control system
will close (BO#11) on the main control board (MCB), thus
energizing relay (R20). When 120V power is furnished
through the system on/off switch (S1), through the burner
on/off switch (S3), through relay (R20) contacts, through the
high limit control (FLC) and through the optional automatic
reset low gas pressure switch (LP5) and the optional manual
reset high gas pressure switch (HP5), terminal #6 on the
flame safeguard (FSG) is powered. The flame safeguard
then energizes its terminal #4, which powers the burner com-
bustion air blower motor (BM). Whenever power is restored
to the flame safeguard, the flame safeguard will go through a
10 second initiation period before the prepurge period will
begin.
The burner air control valve will be at minimum position
during off cycles. Upon a call for heat or any other time that
a prepurge cycle occurs the air control valve will be re-posi-
tioned to the maximum position for the prepurge and then
returned to the minimum position for low fire start.
(VM1), through the N/C contacts of (R20) and (R23), posi-
tions the burner air and gas control valves to minimum after
run cycle. When (R20) is energized for a new call for heat,
(VM1) through the N/O contacts of (R20) and the N/C con-
tacts of (R21), will re-position the burner air valve to its
maximum open position for pre-purge. When the air control
valve reaches the full open position switch (LS2) is 'made',
powering (FSG) terminal #7 through the burner air switch
(AS). This initiates the 60 second prepurge cycle. Concur-
rently, (LS2) powers timer (TD10) which will energize relay
(R21) after 20 seconds. When (R21) is energized (VM1) will
start the air control valve on its way toward the minimum air
valve position through the N/O contact of (R21) and the N/C
contact of (R23). At the completion of the 60 second
prepurge cycle the valve will be at the minimum open posi-
tion and the minimum position switch (LS1) will be
'MADE'. If (LS1) is not 'MADE' the combination gas control
start valves (GV1) will not open and the burner will go out
on safety lockout.
After completion of the 60 second prepurge period there will
be a 10 second trial for ignition during which terminal #8
(combination gas valve - GV1) and terminal #10 (ignition
transformer - IT) will be energized. If flame is being
detected through the flame rod (FD) at the completion of the
10 second trial for ignition period terminal #10 (ignition
transformer - IT) will be de-energized and terminal #9 (relay
R23 coil and main gas valves - GV4 and GV5) will be ener-
gized and the control system will be allowed to control the
firing rate. The flame safeguard contains 'LEDS' (lower left
corner) that will glow to indicated operation.
After the flame has lit and been proven, relay (R23) is ener-
gized allowing (VM1), as controlled by (BO#9) and
(BO#10) on the main control board (MCB) to position the
burner air and gas valves for the required firing rate. When
the main control system closes (BO#10) the gas valve actua-
tor will re-position toward a higher firing rate until (BO#10)
opens or the actuator reaches its maximum position. When
the main control system closes (BO#9), the actuator will re-
position toward a lower firing rate. If neither (BO#9) or
(BO#10) on the main control board (MCB) are closed, the
actuator will remain at its present position. The heating
capacity is monitored by the main control board (MCB)
through (AI #10) via a position feedback potentiometer on
the actuator.
In the event the flame fails to ignite or the flame safeguard
fails to detect its flame within 10 seconds, terminals #4, 8, 9,
and 10 will be de-energized, thus de-energizing the burner
and terminal #3 will become energized. The flame safe-
guard would then be on safety lockout and would require
manual resetting. Terminal #3 will energize the heat alarm
relay (R24), which would then energize the remote 'HEAT
FAIL' indicator light and send a fail signal to binary input #5
in MicroTech II main control board (MCB).
If an attempt is made to restart the burner by resetting the
flame safeguard, or if an automatic restart is initiated after
flame failure the earlier described prepurge cycle with the
wide open air valve will be repeated.
If the unit overheats, the high limit control (FLC) will cycle
the burner, limiting furnace temperature to the limit control
set point.
TEST
CONN.
BURNER
BLOWER
AIR
SWITCH
MODULATING
ACTUATOR
V
v
TEST
COCK
VENT
(OPT.)
HP5
HI PRESS.
SWITCH
COMBINATION GAS CONTROLS
GV1B GV1A
GV4B GV4A
GV5B GV5A
(OPT.)
CAPPED LEAK
TEST COCK
GV1 - HT 020 TO 200
GV4 - HT 040 TO 200
GV5 - HT 079 TO 200
GV6 - HT 110 TO 200
GV7 - HT 140 TO 200
GV8 - HT 200 ONLY
VENT TO
ATMOSPHERE VENT
(OPT.)
GV3
SAFETY
VALVE
(OPT.)
GV2
SAFETY
VALVE
(OPT.)
N.O. VENT
VALVE
(OPT.)
LP5
LO PRESS.
SWITCH
(REQ'D FOR
OVER .50 PSI)
(OPT.)
HIGH PRESS.
REG. SHUTOFF
COCK
VENT
Figure 6b. Typical Piping Schematic

12 IM 685-1
Flame Safeguard
See manufacturer's bulletin for more detailed information on
flame safeguard RM7895A.
The Honeywell RM7895A is a microprocessor based inte-
grated burner control that will perform self-diagnostics, trou-
bleshooting, and status indication, as well as the burner
sequencing and flame supervision.
Keyboard Display Module
The Honeywell S7800A1001 module is an optional device
available for use with the RM7895A. It can be a permanent
accessory added to the RM7895A or it can be carried by the
service technician as a tool that is very easy to mount when
servicing the RM7895A. It mounts directly onto the
RM7895A and has a 2 row by 20 column display. The module
will indicate flame signal dc volts, sequence status, sequence
time, hold status, lockout/alarm status, total hours of opera-
tion, total cycles of operation, and can provide 127 different
diagnostic messages for troubleshooting the system.
The module will give a fault history. It can be mounted to the
RM7895A and will retrieve information on the six most
recent faults.
Consult the Honeywell bulletin 65-0090-1 "7800 Series,
Keyboard Display Module" and 65-0118-1 "7800 Series,
System Annunciation, Diagnostics and Troubleshooting".
Operation
Initiate Period: When the relay module is powered it goes
through a 10 second "Initiate" period. It will also enter into
the "Initiate" period if electrical power problems such as low
voltage or momentary interruption occur while the unit is
operating. Operation of the burner fan motor is delayed
throughout the "Initiate" period.
Standby: After the initiate period is completed the module
will enter the standby mode and await a call for heat by the
temperature control system.
Normal Start-up:
Prepurge: Upon a call for heat the prepurge period will
begin. If the air switch does not detect fan operation in the
first 10 seconds into the prepurge period a recycle to the
beginning of the prepurge will occur.
Ignition Trial: The "start" combination gas control and the
ignition transformer are powered for 10 seconds following
the prepurge. Flame must be proven at the end of that 10 sec-
ond period or safety shutdown will occur.
Run: If flame is proven at the end of the 10 second ignition
trial the "start" combination gas control will remain powered
and on multiple valve units, the other parallel piped main
valves will become powered. If a flameout occurs the mod-
ule will recycle within 3 seconds, and initiate a new prepurge
period. If flame continues to be detected the module will be
in Run until the power is interrupted to terminal 6 indicating
that the temperature control system no longer requires heat,
or that the high limit or another safety control has opened.
LED Display
There are five labeled LED's located on the front of the
RM7895A which are energized to indicate operation as follows:
POWER The RM7895A is powered.
PILOT The prepurge period is complete and the terminal
for the "start" combination gas control is powered.
FLAME Flame is detected.
MAIN The ignition trial period is complete, flame is
detected, and the terminal for the main gas valve
is powered and a normal recycle is underway.
ALARM The RM7895A is on safety lockout.
NC
NO
LS2
C
C
NC
NO
LS1
123
456
C1 C2
123
456
C1 C2
123
456
C1 C2
2 4
13
R22
TD 10
1
2
TB 11
12345678910
11 12NB NB
IGNIT.
TRANSF.
R21
R23
R20
WIRES
FROM
MAIN
BOX
AIR
SW.
S3
4
1710
1185
2
CONTROL
BOX
SWITCH
COMPARTMENT
CONROL BOX
COVER
(SHOWN OPEN)
Figure 6c. Typical Burner Control Box Figure 7. RM7895A Flame Safegaurd

IM 685-1 13
Service
General
Before starting service on this burner take the time to read
the sections "About This Burner" and the 'Sequence of Oper-
ation" to get an overview.
Gun Assembly
The McQuay gas burner gun assembly is easily removable
and includes the ignition electrode assembly, the flame rod
assembly, and a "Base Air" fitting with orifice. The position-
ing of this assembly is not considered field adjustable. When
positioned correctly the gun disc will be perpendicular to the
blast tube and back in the cylindrical portion of the blast tube
as shown in Figure 8. The gun pipe will be concentric with
the blast tube.
Figure 8. Gun Assembly
Gun Assembly Removal and Installation
Unplug the ignition lead from the ignition electrode and
unplug the flame rod lead from the flame rod. Disconnect the
3/8 inch copper tube at the brass fitting on the left side of the
gun pipe, open the pipe union and remove the gun assembly.
Models 050-200 include an air tube that must be lifted up
and out of the grommeted hole it is nested into as the gun
assembly is removed. The gun assembly may have to be
manipulated and wiggled as the disc is withdrawn back
through the blast tube. Reassemble in reverse order, being
particularly careful to correctly reinsert the air tube into the
grommeted hole. The tube should slip into the grommet so
there is little leakage, but it should not bear down on it or it
can cause binding on the sliding air valve. Always remove
shoulder screw (12), Figure 16a, and manually slide the con-
trol rod back and forth to test for binding after reinstalling
the gun assembly on Models HT050-200. Do not operate the
burner without a tight seal at the grommet.
Flame Rod Adjustment
The gun assembly is removed for flame rod inspection or
service. When correctly adjusted the flame rod insulator will
be concentric with the hole it passes through, not be shorted
out against the disc, the 0.75 inch long end tip will point
toward the 0.086 inch diameter alignment hole, and the end
tip will clear the disc according to dimension 'C' Figure 9.
Figure 9. Flame Rod and Ignition Electrode
Flame Rod Installation
The flame rod must be disassembled from its porcelain insu-
lator for removal or installation. Remove the two nuts on the
threaded end of the flame rod, pull the rod out of the insula-
tor, and then remove the insulator by loosening its clamp
screw.
Ignition Electrode Adjustment
The gun assembly is removed for ignition electrode inspection
or service. When correctly adjusted the ignition electrode
insulator will he concentric with the hole it passes through, the
end of the insulator will be flush with the outside surface of
the gun disc, the electrode tip will point toward the 0.086 inch
diameter alignment hole, and there will be a 0.09 inch spark
gap to the gun disc (see Figure 9). The ignition electrode can
he removed by loosening the clamp screw and sliding the
entire assembly through the disc hole.
Model HT*** A B Base Air
Orifice I.D.
020 1.98 1.94 .060
025 2.04 1.88 .060
032 2.04 1.88 .067
040 2.17 1.75 .070
050 2.17 1.75 .089
064 217 1.75 .089
065 2.17 1.75 .089
079 2.07 1.85 .102
080 2.07 1.85 .102
100 2.30 1.62 .102
110 2.24 1.68 .098
140 2.30 1 62 .110
150 4.13 1.62 .110
200 4.13 1.62 .110
Model HT*** C
020 .09
025 .09
032 .09
040 .09
050 .40
064 .40
065 .40
079 .40
080 .40
100 .44
110 .35
140 .35
150 .48
200 .75
BASIC AIR
ORIFICE
AB
ALIGN FLAME ROD TIP
WITH .086 DIA HOLE
IN BURNER DISC.
.086 DIA.
HOLE (REF.)
ALIGN IGNITION
ELECTRODE TIP
WITH .086 DIA HOLE
IN BURNER DISC.
.086 DIA. HOLE
(REF.)
.09
C
FLAME ROD
IGNITION
ELECTRODE

14 IM 685-1
Air and Gas Adjustments
The burner has been adjusted and tested at the factory with
accurate instruments. There should not be a need to readjust
the burner after the unit has been installed.
Verify that the gas supply pressure is correct, the electrical
power is correct, and test the burner thoroughly. Do no make
adjustments unless there is a clear indication that there is a
problem, and proper instruments are available so the adjust-
ments can be made correctly.
Gas Supply Pressure
The maximum pressure rating of the combination gas con-
trol(s) used on this burner is 0.50 psi (13.9 in. w.c.), as mea-
sured at (2), Figure 16a. If the gas supply pressure is higher
than this an additional regulator must be installed so the
pressure will not exceed 0.50 psi.
Many gas burner problems are due to gas supply pressure
problems. High or low gas pressures can cause nuisance
lockouts of the flame safeguard and combustion problems.
Low gas pressure will reduce the heat output of the furnace,
and if extreme, can cause combustion problems and flame
safeguard lockouts. Every gas supply system has a high pres-
sure regulator somewhere upstream. Perhaps it is at the
meter and adjusting the outlet pressure is not an option, the
following discussion on the "High Pressure Regulator"
would still apply.
High Pressure Regulator
If a high pressure regulator is included as part of the burner
gas train or is included elsewhere in the gas supply line, it
should be adjusted so the pressure at the inlet tap to the com-
bination gas valves is 7.0 in. w.c. The inlet tap is (2) on Fig-
ure 16a. Check that the pressure is relatively consistent as
the firing rate changes. If any other equipment is served by
that same gas line or pressure regulator, check that the gas
pressure also remains relatively consistent when that equip-
ment is turned on and off. Verify that the regulator closes off
tightly at zero flow by observing that the pressure does not
creep up when the unit is off. If it does, excessive pressure
will have built up over the off period, possibly exceeding the
pressure rating of the combination gas controls, and causing
other problems at light off.
Gas Adjustments
See the sections on "Gas Valve Pressure Regulator Adjust-
ment", "Gas Supply Pressure", and "High Pressure Regula-
tor". The gas flow rate is determined by the gas pressure and
a characterized element within the modulating gas valve.
The stem of the valve connects to the bracket that positions it
with lock nuts that are adjusted at the factory and determine
the minimum firing rate of the burner. Other than gas pres-
sure adjustments, this is the only adjustable control of the
gas. Adjusting the minimum rate is not intended to be a rou-
tine field adjustment. Properly adjusting the minimum rate
requires clocking a gas meter at very low flow rates, or con-
necting a test flow meter into the gas train.
Air Adjustments
Airflow and the resultant combustion characteristics have
been preset and tested at the factory and no further adjust-
ments should be required. Airflow to the burner is deter-
mined by the characterized plate on the air valve outlet (1)
and an adjustable plate (2) on Figure l0a. The adjustable
plate can increase or decrease airflow across the entire stroke
of the valve. If burner airflow is in question, measure the
static pressure at Ports (4) and (5), Figure 16, and compare
those readings with Columns 6 and 8 in Table 5. A signifi-
cant difference should be checked out.
Air and Gas Control Linkage
An L-shaped control rod is connected to the actuator and
passes through the burner housing and into the control box.
This control rod positions the valves that control the burner
air and gas, and actuates switches in the control box to prove
when it is at the maximum and minimum position. When the
actuator positions the control rod to the minimum rate posi-
tion, the bracket on that rod that connects to the air valve and
gas valve should be firmly bottomed against the end of the
gas valve which acts as its stop. The linkages to the air and
gas valve should be straight and in alignment. Although the
bracket is to bottom out, the plate connected to it which
slides from right to left to control airflow should slide freely
and not be forced against either the right or left side member
of the air box.
At the minimum rate position maintain a gap according to
dimension "D", Figure 10a. With that sliding plate in this
minimum rate position, check dimension "E", Figure 10a. To
gauge opening "E", use a drill blank held perpendicular to
the plate. For Models 050-200 opening "E" can be accessed
through the grommeted opening in the primary air collector.
See (3), Figure 10a. for Models 020-040 the primary air col-
lector must be removed. Generally, it is easier to remove the
collector with the inch diameter tube still attached by discon-
necting the tube at the other end.
At the maximum rate position the sliding blade should be
full open, but it should not be forced against the left side
piece of the air box.
The control rod bracket that connects the air and gas valves
must be correctly positioned on the control rod such that the
bracket will be firmly held under tension against its stop
when the actuator is in the minimum rate position, and so the
sliding blade will open fully without making contact at the
end of the stroke. When modulating towards the minimum
rate position the actuator will continue to travel after the
bracket contacts the stop, flexing the vertical end of the con-
trol rod so the bracket is held under tension. To correctly
locate the bracket on the rod, first adjust the air damper link-
age so there will be a gap per dimension "D", Figure 10a,
when the bracket is bottomed out against the end of the
valve. Second, loosen both set screws on the bracket assem-
bly so the bracket is free to slide on the rod. Third, position
the actuator to the maximum rate position. Position the slid-
ing blade to the wide open position.

IM 685-1 15
Grasp the rod and while applying some thrust to the rod in
the direction of the actuator to take up any free play, and
with the bracket in alignment with the linkages that connect
to it, tighten the two set screws. Return the actuator to the
minimum rate position.
The adjustable plate (2), Figure 10a is positioned to provide
an opening per dimension "F".
Figure 10. Air and Gas Control Linkage
Actuator Crankarm
The actuator crankarm should not require adjustment. The
radius indicated by "G" dimension, Figure 10b will result in a
complete stroke from minimum to maximum, and provide the
correct amount of over travel to bottom out the linkage
bracket at the minimum rate position. Do not attempt to mod-
ify firing rates, etc. by changing the radius of the crackarm.
Switch Adjustment
Switches LS1 and LS2 prove maximum and minimum posi-
tion of the control rod. These switches are located in the con-
trol box switch compartment and have a limited range of
adjustment. When the two nuts that secure the switches are
loosened the switch will pivot on the inner stud and the outer
stud can be moved up and down. The switches should be
adjusted such that when the collar mounted on the actuator
rod is moved into position and pushes in the lever on the
switch, the switch will click to the "made" position, but the
lever will not bottom out against the switch body. When
properly adjusted the lever can move an additional 0.02
inches, as proven by slipping a feeler gauge between the
switch lever and the collar when in the "made" position. The
collar on the control rod should be adjusted so the switch
lever it is actuating will rest squarely on the outer surface of
the collar but only 0.03 inches from the edge. If the collar is
located for an engagement that is longer than 0.03 inches,
the collar may not reach the actuator on the other switch
when at the other end of its stroke.
Altitude Considerations
For altitudes of 2000 feet and higher, the gas burner must be
derated 4% for every 1000 feet of altitude.
Example: Model HT080 at an altitude of 3000 feet is derated
(0.04 x 3 = 0.12). At 1000 mbh input (1000 x 0.12 = 120
mbh), the actual input is (1000 - 120 = 880 mbh) at 3000 feet.
The method of derating the burner is to reduce the manifold
pressure. Multiply the Maximum Rate Manifold Pressure
shown under Column 8 in Table 5 by the following altitude
factors:
2000 feet = 0.845 5000 feet = 0.640
3000 feet = 0.774 6000 feet = 0.578
4000 feet = 0.706 7000 feet = 0.518
Model
HT*** DE F G
020 .005 .116 .50 3.30
025 .005 .125 .83 3.30
032 .005 .101 .82 3.30
040 .005 .101 1.25 3.30
050 .020 .099 1.25 3.30
064 .020 .136 1.60 3.30
065 .020 .136 1.60 3.30
079 .020 .106 1.88 3.30
080 .020 .106 1.88 3.30
100 .020 .110 2.44 3.30
110 .020 .136 1.05 4.28
140 .020 .136 3.30 4.28
150 .020 .140 3.30 4.28
200 .020 .140 4.40 4.28
90º
10º G
MIN
RATE
c
PROFILE
PLATE
d
ADJUSTABLE
PLATE
e
PRIMARY AIR
COLLECTOR
E
FD
Figure 10b

16 IM 685-1
Gas Valve Pressure Regulator Adjustment
The high turndown burner uses combination gas controls to
provide redundant on-off gas control and pressure regulation.
A burner will have from one to six of these controls piped in
parallel depending on the BTU rating of the burner. When
two or more valves are in parallel their pressure regulators
must be adjusted so the valves maintain the specified mani-
fold pressure and are balanced so each valve handles its share
of the load. To determine that the valves are balanced, the
manifold pressure must be measured and adjustments made
at both maximum and minimum capacity. As the burner mod-
ulates from maximum capacity down to minimum capacity it
is normal for the manifold pressure to rise. This is because
the pressure loss through the valve and fittings is being
reduced as the flow rate is reduced. If one (or more) valve is
not in balance with the others, the pressure at the minimum
rate will rise higher than normal.
Clockwise rotation of the pressure adjusting screw on the
combination gas controls will increase the pressure set point,
and counter-clockwise rotation will reduce the pressure set
point (see Figure 11).
Figure 11. Combination Gas Controls
Adjustment Procedure for Parallel Valves
When a manifold pressure adjustment is required, the first
step is to adjust the pressure regulator of each combination
gas control to the minimum rate manifold pressure (Table 5,
Column 10) while only that valve is operational, and it is
handling approximately its normal maximum rate CFH of
gas. The manual shutoff valve knobs are used to control gas
flow so just one valve is operating at a time.
To determine a firing rate suitable for this adjustment, first
modulate the burner down to the minimum rate. At this flow
rate only the valve with the highest pressure regulator set
point will be operational, the other valves will be shut down
by their integral pressure regulators because the manifold
pressure is slightly higher than their set point. While the
burner is operating at that minimum firing rate slowly close
all but one of the manual shutoff valve knobs on the combi-
nation gas controls. With care this can be done without the
burner loosing flame and shutting down. Watch the manifold
pressure manometer as each valve is being closed. If the
manifold pressure starts to drop rapidly in response to the
knob movement, it indicates this combination gas control has
the higher pressure adjustment and is supplying the gas to the
manifold. Leave this valve open, and continue closing the
remaining valves until only that one valve is open, and then
adjust that combination gas control first.
While the burner is operating and only one combination gas
control is open, increase the firing rate of the burner. As the
firing rate is increased the manifold pressure will be rela-
tively constant until the gas flow rate exceeds the capacity of
that single valve and the manifold pressure starts to drop off.
The pressure adjustments should be made at the maximum
gas flow rate just before the manifold pressure starts to drop
off, and the following should be considered:
a. The manifold pressure does not always immediately
respond to regulator adjustments. Wait a few seconds after
making an adjuster movement for the regulator to respond
and equalize.
b. When making an adjustment rotate the adjuster CCW
until the manifold pressure is below the desired set point,
and then slowly rotate the adjuster CW and nudge the
pressure up to the desired set point.
c. If the regulator cannot be adjusted up to the required set
point, or if that set point seems to be the highest pressure
the regulator can be adjusted to, the flow rate used for this
procedure is too high and must be reduced by reposition-
ing the actuator to a lower firing rate, or the gas supply
line pressure is too low.
After adjusting valve 1, open valve 2. If opening the addi-
tional valve does not cause the manifold pressure to go up,
increase the pressure regulator setting of valve 2 until an
increase is observed, this would indicate that the valve has
started functioning. Then slowly close the first valve. Pro-
ceed to adjust valve 2. Repeat this procedure until all valves
have been adjusted.
Open the manual shut off knobs on all the combination gas
controls and modulate the burner up to the maximum firing
rate. The resulting manifold pressure should be close to the
Maximum Rate Manifold Pressure indicated in Table 5, Col-
umn 6. If further adjustment is required it should not be nec-
essary to go through the entire procedure again. If the
manifold pressure is to be increased, make small but equal
(about 1/4 revolution) CW rotations of the pressure adjusting
screw on every combination gas control and check the result-
ing manifold pressure, both at maximum and minimum rate.
Check Manifold Pressure at Minimum Rate
When several combination gas controls are in parallel and are
handling a low flow rate, the combination gas control with
the highest set point is essentially handling all the gas.
Observe the gas manifold pressure at the minimum rate. If it
is higher than the pressure specified under Column 10 in
Table 5, locate and adjust the dominant combination gas con-
trol. Test each combination gas control by slowly manipulat-
ing the manual shutoff knob toward the closed position while
observing the manifold pressure. The pressure will only
respond to movement of the knob on the dominant valve. The
manifold pressure will drop as the gas flow is throttled back,
using the knob on the combination gas control to partially
close that manual valve.
PRESSURE REGULATOR ADJUSTMENT
(UNDER CAP SCREW)
INLET
PRESSURE
TAP
GAS
CONTROL
KNOB
OUTLET
PRESSURE
TAP
(SHOWN AT "ON")
INLET OUTLET
ON
OFF

IM 685-1 17
Generally a valve will he found that has an effect, and very
little adjustment will cause a reduction in the minimum rate
manifold pressure. Reduce the pressure adjustment of that
dominant valve by slowly rotating the adjuster CCW until
the manifold pressure no longer drops in response to that
adjuster movement. If the manifold pressure is still high after
that first adjustment, another valve may have become the
dominant valve and that may also have to be isolated and
adjusted to get down to the specified minimum rate manifold
pressure. After making this type of adjustment it is necessary
to recheck the maximum firing rate manifold pressure and
perhaps readjust it, making very small but equal adjuster
movements on each valve.
Combustion Testing
Proper start-up and maintenance requires periodic combus-
tion tests and the systematic recording of those test results
for future reference. Before making combustion air adjust-
ments, check for proper input rate.
Verify Input Rate
To determine the input rate it is necessary to know the BTU
per cubic foot of gas being used. If this is not known, contact
the gas supplier. Check input rate by timing the gas meter
dial with all other appliances and their pilot lights off.
To verify the input rate using the gas meter, use a stopwatch
and time one revolution of the dial. Calculate the input with
the following formula:
MBH Input= A x B x 3.6
C
Where: A = BTU/cu. ft. of gas
Typical: Natural gas= 1000, LP gas=2500
B = Cu. ft. per revolution of meter dial
C = Seconds required for 1 revolution of meter dial
Check CO2, CO & Stack Temperature
Flue gas samples are to be taken from inside one of the sec-
ondary tubes. If the sample is taken from the flue box rather
than the tube, the sample will be diluted with outside air and
lower readings will result. If flue gas temperature is to be
measured, this must be done in the flue box, not in the tube.
The temperature gradient within the tubes would cause high
readings near the center of the tube and low readings near
the edge. Temperatures should be measured within the flue
box where a good mix will be present. The flue box includes
two 5/16" holes for test purposes. One hole lines up with the
end of a secondary tube for taking flue gas samples. The
other hole, through the side of the flue box, is for thermome-
ter insertion.
If the CO2and/or CO readings are not within the range indi-
cated, see "Troubleshooting Guide," Section 4.1 and 4.2.
Figure 12a Figure 12b
Typical Readings:
CO29½to 10½percent at maximum rate
4 to 7 percent at minimum rate
CO .005 percent (50 PPM) or less
Cleaning Heat Exchangers
Models 032 thru 200 (see Figure 13)
1. Remove the flue box front wrap (1) and the rear inspec-
tion cover (3).
2. Remove and clean the turbulator (2)‚ from each tube and
clean the flue box.
3. Clean each tube with a 2½" round flue brush.
4. Remove the brushings and if required clean the combustion
chamber and header through the rear inspection door port.
Figure 13. Models 032 thru 200 Heat Exchanger
5. Reinstall the inspection door (3). Snug the screws but do
not overtighten and crush the insulation.
6. Reinstall a turbulator (2) in each tube approximately
flush with the tube ends. The end of the turbulators are
formed such that the end will bind within the tube end
and lock the turbulator in place.
7. Reinstall flue box front wrap (1) .
300º
400º
500º
600º
Temperature Gradient
within Tube
Co2
Sample
Measure
Temperature
3
2
12 1/2 Round Flue Brush With 7 Foot Handle

18 IM 685-1
Models 020 thru 025 (see Figure 14)
1. To gain access to the inside of the combustion chamber,
detach the burner from the furnace and set it on the floor
of the vestibule (see Figure 14, Item (3)). The burner is
attached to the furnace studs with four nuts. Conduit
lengths allows this movement of the burner without dis-
connecting wiring. The union on the gas line must be
opened.
2. Remove the flue box front wrap (1) .
3. Remove and clean the turbulator (2) from each tube and
clean the flue box.
4. Clean each tube with a 2½" round flue brush.
5. Remove the brushings and if required clean the combus-
tion chamber and header through the burner mounting
tube.
6. Reinstall the burner.
7. Reinstall a turbulator in each tube approximately flush
with the tube end, locking them in place with the wedge
clips on each turbulator.
8. Reinstall flue box front wrap (1).
Figure 14. Models 020 thru 025 Heat Exchanger
Leakage Symptoms
1. Odor - Odors in the building are usually being brought in
through the outdoor air intakes and do not indicate leak-
age from the furnace. Check for down draft conditions
and check the location of the flue exhausts of other equip-
ment that may be pulled into the outdoor air intake. A
major and obvious furnace rupture can be a source of
odor. In general, small leaks in a furnace will not be a
source of odor or danger because the pressure created by
the supply fan is greater than the pressure inside the fur-
nace. Therefore when the supply fan is operating, leakage
will be into the furnace, not out of the furnace and into
the air stream. If the control system is such that the fur-
nace comes on and warms up the heat exchanger before
the supply air fan comes on, and there is odor when the
supply fan first comes on, this could be caused by leak-
age. During the time the furnace is on and the supply fan
is off the leakage would be out off the furnace and then
when the supply fan came on it would blow those prod-
ucts of combustion into the supply duct.
2. Low CO2Readings - Low CO2readings that cannot be
corrected can be caused by air leaking into the heat
exchanger and diluting the flue gas. If this is suspected,
take two consecutive CO2readings, one with the supply
fan running and one with the supply fan off. If the CO2
increases with the supply fan off, it could indicate leak-
age. Note that CO2samples must be taken from inside a
tube, not just from inside the flue box.
Checking for Leaks
1. Open up the rear casing panel while the unit is shut off
and visually inspect the heat exchanger.
2. Visually inspect the heat exchanger while the burner is
operating, looking for light coming through holes. The
burner should only be operated for a few minutes with the
supply fan off, and take necessary safety precautions
around the hot heat exchanger.
3. Perform consecutive CO2tests with supply fan off and
on. See Item 2 under "Leakage Symptoms."
4. Smoke Bomb Test - Cover the flue box openings, open
the rear casing panel so the heat exchanger is accessible,
toss a smoke bomb into the heat exchanger through the
rear inspection port, replace the port cover, and with a
bright light look for smoke leaking through the heat
exchanger. Remove the remains of the smoke bomb and
uncover the flue box openings before attempting to oper-
ate the furnace.
Note: In most cases small leaks in the heat exchanger are not
a source of danger. Because the pressure created by the sup-
ply fan is greater than that inside the heat exchanger, the
leakage will be into the heat exchanger, not out of the heat
exchanger and into the airstream.
Causes of Failures
1. Improper Application - The furnace rating plate speci-
fies a "Minimum Airflow CFM." The furnace must not be
operated when airflow is below this minimum cfm. If the
furnace is being used on a variable air volume system, the
control system must be such that the furnace will not
operate when the supply fan cfm has fallen below this
minimum specified cfm. The furnace rating plate also
specifies a "Maximum MBH Input" which must not be
exceeded. See "Verify Input Rate."
2. Control Failure - The limit control does not function
properly to shut off the burner when the heat exchanger
temperature becomes excessive. In most situations, a
properly controlled unit will never even require the limit
control to shut off the unit. The limit control should be a
backup control and a problem attributed to a limit failure
would generally indicate a control problem in addition to
the limit failure.
3
2 1/2 Round Flue Brush With 4 Foot Handle
2
1
Condensate Drain
Wind Deflector

IM 685-1 19
3. Excessive Condensation - Applications which will pro-
duce condensation require an all stainless steel heat
exchanger that is resistant to the effects of this condensa-
tion and that will give long heat exchanger life. The like-
lihood of condensation increases with:
a. Colder supply air temperature across the secondary
tubes, as on units taking in a lot of outdoor air in
colder weather.
b. Lower heat flow through the secondary tubes, as on
modulating burners when operating at reduced input.
c. High airflow across the secondary tubes such as any
application with a low temperature rise furnace.
4. Chemical Deterioration - Refrigerant leaks, some aero-
sol can propellants, fumes from dry cleaning establish-
ments, beauty shops, swimming pools, and others, often
have detrimental effects on heat exchangers when they
get into the combustion air supply and thereby into the
combustion. Even fumes from nearby roof exhaust fans
can cause problems.
5. Inadequate or Distorted Airflow - Internal baffles that
have been repositioned or have loosened up and moved
can distort the airflow and cause failures. Construction
rubbish, shipping cartons, and insulation that has come
loose will occasionally end up inside a unit and block air-
flow to part of the furnace, resulting in a failure. These
items can also alter the air or heat flow to the fan limit or
some other control and contribute to a failure.
Replacing Heat Exchanger
1. Remove the complete flue box, the casing panel through
which the flue tubes pass, and the rear inspection cover.
Open the hinged rear door.
2. The burner is mounted on and supported by the heat
exchanger studs with four nuts. When removing the heat
exchanger, the burner must either be removed or blocked
in place. Remove the four burner mounting nuts and the
two exchanger bolts located 2" above the upper burner
mounting nuts.
3. When it is necessary to remove any air baffles surround-
ing the heat exchanger, carefully note the locations and
clearances of these baffles before removing them so they
can be replaced in the exact same position.
4. Remove the two bottom bolts at the back of the heat
exchanger.
5. Withdraw the heat exchanger through the back of the casing.
Furnace Condensation
A furnace will produce condensation when the flue gas tem-
perature falls below its dew point temperature. A more effi-
cient furnace will transfer more of its heat into the building,
and leave less heat in the flue gas. This results in a lower flue
gas temperature and more condensate.
A modulating burner will produce more condensate than an
on-off burner. As the firing rate of the burner is reduced the
flue gas temperature will he reduced, and if it is reduced
below its dew point condensate will be produced.
A furnace that is heating a high percentage of outside air will
also produce more condensate. The colder the air contacting
the heat exchanger, the lower the resulting flue gas tempera-
ture, and consequently the more condensate.
Do not think a furnace has a problem because it produces
condensate anymore than you would think a cooling coil has
a problem because it produces condensate. However suitable
steps should be taken to manage the flow of the condensate
produced.
Most condensate will be produced in the secondary tubes
where flue gas will sweep it into the flue box. Condensate
will also come from the combustion chamber. Models 020
and 025 have a piped combustion chamber condensate drain,
and Models 032 through 200 have a rear cleanout port with
an integral condensate drain.
On a properly prepared unit, the condensate should drip from
drain openings in the two outer corners of the flue box, and
from the drip shield below the rear cleanout port. Condensate
should not be running down the unit, except at times the
wind may blow the dripping condensate mentioned above.
At installation the flue box should be sealed with high tem-
perature silicone (see "Installation - Flue Box, Item 3"). The
drip shield below the rear cleanout port must be correctly
installed. See following section: "Rear Cleanout Port".
Rear Cleanout Port - Figure 15a
The rear cleanout port is equipped with a stainless steel drip
shield to channel the flow of condensate coming out the
cleanout port (see Figure 15). The shield (1) must fit snugly
against the bottom of the cleanout port tube (2) at (3) so con-
densate (4) cannot run back along the underside of the tube
and into the unit or down the side of the rear panel. Instead,
the condensate is to run down the drip shield and be directed
into the spout.
Figure 15a. Rear cleanout port (models 032 thru 200)
3
1
2
4
2
3
1

20 IM 685-1
Figure15b. Condensate Drain Retrofit Kit
Furnace Condensate Drain kit - Figure 15b
Considerations:
It is possible that condensate will freeze within the conden-
sate drain tube and this should be considered, particularly if
planning to extend the condensate drain tube beyond the ver-
tical piece furnished. Freezing is influenced by the fact that
the condensate leaving the furnace is hot, that it is accompa-
nied by a discharge of hot flue gas, and that during cold
whether the furnace will operate at a higher firing rate and
may not produce condensate.
If the tube does freeze and plug, condensation will then exit
where the spout (1) enters the tube, and will run down from
that point until the tube thaws open.
Install.875 Copper Drain Line
1. A length of copper tube is furnished to route the furnace
condensate down the side of the unit to the roof or other
chosen location. The length of copper tube (2) furnished
will extend approximately 2 inches below the bottom of
the unit. The length can be trimmed or fittings added as
required by field conditions.
2. The tapered stainless steel spout (1) at the bottom of the
rear inspection port slips approximately .25 inches into the
upper end of the copper tube (2). Bend the end of the spout
out from the casing panel slightly so the tube can be
slipped into position.
3. The copper tube runs vertically down the side of the unit
and extends approximately 2 inches below the bottom of
the unit base frame. The copper tube can drain onto the
roof or drain into any means of condensate disposal that
has been provided.
4. The tube is attached to the door by a clamp (3) which uses
a No. 10 x 1.50 Lg. stainless steel drill screw (4). The drill
screw hole is located 2.75 inches below the bottom of the
inspection cover, with the exception that several models
are drilled at 3.15 inches below the inspection cover to
avoid the no drill zone.
Install the Cover Channel Over Drain Pipe
1. Locate the copper channel (5) over the drain line. The top
of the channel should be approximately .75 inches below
the bottom of the inspection cover and extend approxi-
mately flush with or somewhat below the bottom of the
unit base frame. The channel is positioned so the mounting
screw holes are on the left.
2. The cover channel for certain models have an edge notch.
This notch is to provide clearance for a bolt head in the
base frame.
3. Attach the channel with two No. 10 x 1.50 Lg. stainless
steel drill screws (6). Pay close attention to the "no drill
zones". There could be wiring in the lower zone, and there
is a door sealing gasket in the upper zone.
Combination Fan and Limit Control
The fan limit control is a hydraulic action type with a remote
sensing element and connecting capillary tube. The sensing
element is locked into a bracket located on one of the heat
exchanger tubes about halfway toward the back of the fur-
nace, on the side away from the blower. One corner of the
bracket is bent aside to remove the element.
Normal setting of the FAN control: FAN On=125°F., Fan
Off=100°F.
The LIMIT control must never be set higher than the temper-
ature listed below. If the burner is shutting off on high limit at
these settings it indicates that there is a problem with the fur-
nace not getting enough air or it is being overfired.
Table 4. LIMIT control set points
.75
5
6
1
4
3
2
2.75*
1.45
.75
.38
NO DRILL
ZONE
*SOME MODELS ARE
3.15" TO AVOID NO
DRILL ZONE
BURNER
MODEL
LIMIT CONTROL
SET POINT
BURNER
MODEL
LIMIT CONTROL
SET POINT
020 215 079 181
025 160 080 229
032 196 100 170
040 154 110 222
050 229 140 168
064 185 150 194
065 232 200 151