Cambridge Air Solutions SPEC AIR Series User manual

SPEC AIR SERIES
DRAW THRU
DIRECT GAS-FIRED
VENTILATION UNIT
TECHNICAL MANUAL
SPEC AIR -TM1-0122
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
The use and storage of gasoline or other flammable vapors and liquids in open
containers in the vicinity of this appliance is hazardous.
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.
Made in the USA
90.1
ASHRAE
ASHRAE
COMPLIANT
COMPLIANT
®

LIMITED WARRANTY
Cambridge Air Solutions Limited Warranty is included within the Terms and Conditions that are
sent with every Order Acknowledgement. For questions regarding Limited Warranty, contact
Cambridge Air Solutions Customer Service Group at 1-800-473-4569.
Copyright © 2022
Cambridge Air Solutions
All Rights Reserved
Cambridge Air Solutions
760 Long Road Crossing Dr.
Chesterfield, MO. 63005
Phone: [phone]
Fax: [phone]
www.cambridgeair.com

SPEC AIR SERIES
TECHNICAL MANUAL
HAZARD SUMMARY..........................................................................................................................................3
TYPICAL SYSTEM OVERVIEW .....................................................................................................................4
Accessory Identification.........................................................................................................................5
Unit/Accessory Weights........................................................................................................................5
Unit Operation.............................................................................................................................................6
Unit Configuration.....................................................................................................................................6
INSTALLATION INSTRUCTIONS
Uncrating Instructions.............................................................................................................................7
Mounting Location....................................................................................................................................7
Horizontal Mount – Mounting Curb .................................................................................................8
Horizontal Mount – Roof Top Preparation.....................................................................................9
Gas Piping....................................................................................................................................................11
Electrical.......................................................................................................................................................12
START-UP INSTRUCTIONS ..........................................................................................................................13
OPERATING INSTRUCTIONS
Operating Sequence.............................................................................................................................20
Electronic Thermostat..........................................................................................................................23
TSS Controller.......................................................................................................................................... 25
MAINTENANCE INSTRUCTIONS
Bearing Lubrication ..............................................................................................................................34
Belt Tensioning .......................................................................................................................................34
Blower Cleaning......................................................................................................................................35
Burner Cleaning ......................................................................................................................................35
Gas Valve Cleaning................................................................................................................................35
ASCO Gas Valves...................................................................................................................................36
Filters ............................................................................................................................................................38
CONTENTS

Cambridge Air Solutions. 2 Spec Air Series Technical Manual
REFERENCE
Unit Roof Openings...............................................................................................................................39
Unit Discharge Dimensions ..............................................................................................................39
Gas Train Drawing..................................................................................................................................40
Electrical Control Enclosure Isometric Drawing (V18 - V30).............................................41
Electrical Wiring Diagrams ................................ ...............................................................................42
Series 44 Temperature Setback System/Temperature Averaging ......................... 42
Connection Diagram.............................................................................................................................43
Gas Control Systems ............................................................................................................................44
Remote Control Station Components..........................................................................................45
Individual Unit Component Descriptions...................................................................................46
Damper Motor Replacement & Adjustment..............................................................................51
Troubleshooting Guide ........................................................................................................................ 52
ANSI/ASHRAE/IESNA STANDARD 90.1 ............................................................................................... 57
MAINTENANCE LOG ......................................................................................................................................58
QR CODE...............................................................................................................................................................59
SPEC AIR SERIES
TECHNICAL MANUAL
CONTENTS

Spec Air Series Technical Manual 3 Cambridge Air Solutions
HAZARD SUMMARY
The following safety precautions apply to the
installation, operation, and maintenance of the
equipment described by this technical manual.
WARNING:
Any unauthorized modification of this
equipment shall void the warranty.
WARNING:
Only qualified personnel should attempt
installation, service, and repair of this
equipment. Use extreme caution and observe
safety regulations at all times. Obey applicable
plant and OSHA safety regulations.
WARNING:
Recirculation of room air is not permitted.
Adequate building relief shall be provided so as to
not over-pressurize the building when the ventilation
air heating system is operating at its rated capacity.
It should be noted that this can be accomplished by
taking into account, through standard engineering
methods, the structure’s designed infiltration rate, by
providing properly sized relief openings, by
interlocking a powered exhaust system, or by a
combination of these methods.
If the failure or malfunction of this unit creates
a hazard to other fuel burning equipment in
the building (e.g. when the unit is providing the
ventilation air to a boiler room), the unit is to be
interlocked to open inlet air dampers or other such
devices.
If the unit is installed such that an inlet duct is
utilized, the duct system must be purged with at
least four air changes prior to an ignition attempt.
IMPORTANT
If in doubt regarding installation or application,
contact Cambridge Air Solutions Customer Service
Group at 800-473-4569 during the hours of 8:00 a.m.
to 5:00 p.m. Central Time, Monday through Friday.
Hazard Identification
Warnings and Cautions appear at appropriate sections throughout this manual. Read these
carefully.
WARNING: Indicates a potentially hazardous situation which could result in
death or serious injury.
CAUTION: Indicates a potentially hazardous situation which may result in
minor or moderate injury. It may also be used to alert against
unsafe practices.
CAUTION: Indicates a situation that may result in accidents with equipment or
property damage only.

Cambridge Air Solutions. 4 Spec Air Series Technical Manual
TYPICAL SYSTEM OVERVIEW
CONTROL SYSTEMS:
MAXITROL SERIES 44
The Maxitrol Series 44 modulation controls maintain
a constant space temperature by increasing or
decreasing the discharge temperature. The Space
Temperature Selector is set to maintain the space
temperature of the heated space by controlling the
unit output between the MIN and MAX setting on
the amplifier. The MIN dial setting determines the
minimum discharge temperature the unit will deliver
(40°F to 80°F). The MAX dial setting determines the
maximum discharge temperature the unit will deliver
(80°F to 140°F).
MAXITROL SERIES 44 / TAMPER PROOF
The Maxitrol Series 44 / Tamper Proof temperature
control system is similar to the Maxitrol Series
44 controls above except the adjustable Space
Temperature Selector control is replaced by
two other controls. The adjustable portion of the
temperature selector is typically mounted in the
Remote Control Station to prevent unwanted tampering
of the temperature setting and the non-adjustable space
sensor is mounted in the space being heated.

Spec Air Series Technical Manual 5 Cambridge Air Solutions
UNIT
DUAL RAIN HOODS
WITH INLET BIRD SCREEN
MOUNTING
CURB
DISCHARGE DUCT
DISCHARGE NOZZLES
ROOF
UNIT
DUAL RAIN HOODS
WITH INLET BIRD SCREEN
MOUNTING CURB
DISCHARGE DUCT
DISCHARGE NOZZLES
ROOF
FILTER SECTION
MOTORIZED
DISCHARGE
DAMPER
TYPICAL SYSTEM OVERVIEW
HORIZONTAL MOUNT ROOF TOP CONFIGURATION
Standard Unit
with Optional
Accessories
UNIT / ACCESSORY WEIGHTS
Horizontal Mount (Weights Shown In Pounds)
Model
Component V18 V20 V25 V30
Base Unit11275 1260 1750 2270
Rain Hood - Dual 120 150 210 310
Filters 20 30 45 60
V-Bank Filter Section 200 215 275 395
Discharge Duct - 50" 65 80 95 110
Discharge Nozzles 20 25 35 50
Discharge Damper 20 25 30 40
Curb 14" 100 120 180 210
3HP motor 70
5HP motor 75
7.5HP motor 120
10HP motor 135
15HP motor 220
20HP motor 230
25HP motor 250
1. Primary drive motor not included

Cambridge Air Solutions. 6 Spec Air Series Technical Manual
UNIT CONFIGURATION
Cambridge Spec Air Ventilation units provide tempered, continuous fresh air
ventilation to a facility to meet occupied space ventilation requirements. Units
can also provide simple freeze-protection heating and intermittent ventilation
during unoccupied times. Units may drive relief dampers or mechanical exhaust
fans via an optional dry contact interlock. An entering air thermostat acts as an
economizer by deactivating burner operation during mild weather.
TYPICAL SYSTEM OVERVIEW
UNIT OPERATION
BLOWER ASSEMBLY
BURNER
VIEWPORT
PROFILE DAMPER BLADES
BURNER ASSEMBLY
MANIFOLD PRESSURE
MEASURING PORT
MANUAL SHUT-OFF VALVE
MODULATING GAS VALVE
/REGULATOR
SAFETY SHUT-OFF VALVE (SSV)
ELECTRICAL / GAS CONTROL ENCLOSURE
SHUT-OFF VALVE (SOV)
MANUAL SHUT-OFF VALVE
ACCESS DOOR (BOTH SIDES)
LEAK TEST PORT
MOTOR AND HEAT SHIELD
DAMPER MOTOR ACCESS
(IF DISCHARGE DAMPER SELECTED)

Spec Air Series Technical Manual 7 Cambridge Air Solutions
INSTALLATION INSTRUCTIONS
UNCRATING INSTRUCTIONS
1. Verify the number of items on the Bill of Lading
versus the number of items received.
2. Check for shipping damage. If damage is found,
immediately file a claim with carrier before
proceeding further. Take photographs of any
damage.
3. Check items received to make sure they agree
with ordering information including verification
of data on the ventilation air unit nameplate.
IMPORTANT
Do not discard any components or accessories.
MOUNTING LOCATION
Verify feasibility of the installation location selected
with respect to accessibility to the unit for service
and maintenance functions. Ensure the positioning
of the unit does not inhibit fork truck operation,
storage rack access, or other operations within
the facility. Ensure the unit inlet and outlet are not
blocked or severely restricted, such that it would
affect the rated airflow through the unit or affect the
desired air distribution pattern of the unit. If upon
review of the proposed installation, a problem is
discovered which may be considered detrimental
to the performance of the unit, or restricts its
serviceability, or deviates from the instructions
or drawings which may be provided, it is the
responsibility of the installer to communicate that
information to the person or persons responsible for
providing the installation instructions or drawings
prior to proceeding with the installation.
IMPORTANT
Field constructed intake accessories should be
designed to minimize the entry of snow and rain.
IMPORTANT
Minimum clearance from the face of the electrical
control enclosure to surrounding grounded surfaces
for service activities is 42". Adequate clearance for
burner removal is also required, which is based on
42" or the length of the burner + 12", whichever is
greater. Access for service functions is also required
on the opposite side of the ventilation air unit from
the control enclosure for a minimum distance of 24".

Cambridge Air Solutions. 8 Spec Air Series Technical Manual
A TO
RAIL C
L
B
CMOUNTING
RAIL
BFILTER SECTION
MOUNTING STAND
ROOF
DOWNBLAST
MOUNTING CURB
INLET SIDE
MOUNTING CURB
7
DISCHARGE DUCT
GASKET SEAL
(PROVIDED)
2 TYP
3 TYP
4 TYP
A TYP
2 x 6 WOOD NAILER
(PROVIDED)
RAIL CROSS SECTION
5
INSULATION & CANT
(BY OTHERS)
3"
7/8" TYP
14"
2 x 2 WOOD NAILER
(PROVIDED)
UNIT BASE
5
INSULATION & CANT
(BY OTHERS)
INSTALLATION INSTRUCTIONS
CURB AND ROOF PREPARATION
V18 - V30
(Shown for Roof Top Configuration - Downblast Application)
Model
Reference
(inch) V18 V20 V25 V30
A33" 33" 33" 33 7/8"
B48 5/8" 54 5/8" 66 5/8" 88 3/8"
See page 9 for drawing
references and
installation instructions.

Spec Air Series Technical Manual 9 Cambridge Air Solutions
INSTALLATION INSTRUCTIONS
CURB AND ROOF PREPARATION
WARNING:
Due to the size and weight of this equipment, it is
recommended that the unit support structure be
reviewed and approved by a qualified structural
engineer and the roof manufacturer before
installing this equipment.
IMPORTANT
Before proceeding with the installation, verify the
feasibility of the location selected with respect
to accessibility to the equipment for service and
maintenance functions.
IMPORTANT
To minimize snow and rain ingestion, position the unit
inlet opposite the prevailing wind.
CAUTION:
To prevent contaminated air from being drawn
into the unit, install the unit’s inlet at least 10
feet from any building exhaust, process exhaust,
sewer stacks, or other sources that would
allow contaminants to be drawn into the unit.
Consult local codes for applicable building code
provisions for ventilation air.
IMPORTANT
The Spec Air Series product line is suitable for
horizontal mount - roof top configurations only.
1. Prepare the roof for installation. (See page 9
for roof opening dimensions for your specific
unit.) The gas and electrical connections
must not penetrate the unit base or mounting
curb. Cambridge Air Solutions recommends
using pitch pockets or roof boots to seal the
penetrations.
IMPORTANT
Accurate measurements are critical and will affect
installation process.
Roof Opening
Model W (inch) L (inch)
V18 26½" 26½"
V20 30½" 30½"
V25 36" 36"
V30 42" 42"
2. Place exterior curb sides together as shown and
secure using large Tek screws (as required).
3. Install the curb/duct cross supports as shown
and secure using large Tek screws (note
dimension locations).
4. Install the center supports as shown and
secure using large Tek screws note dimension
locations.
5. Insulation and cant (if required) by others.
IMPORTANT
Gas and electrical connections must not penetrate
unit base or mounting curb. Pitch pockets or roof
boots (by others) recommended.
FILTER SECTION ONLY
A. Secure mounting stands to rail wood nailer
with wood lag screws and add waterproof
sealant.
B. Mounting stand construction: 12 Ga.
galvanized steel. Required for filter section
installation.
C. Mounting rail construction: 16 Ga. galvanized
steel. Required for filter section installation.
6. Secure the roof curb (and mounting rail if
required) to the support structure per the
recommendations of the structural engineer and
roof manufacturer.
IMPORTANT
The roof curb or support structure should be
installed such that the unit will sit level.
7. Install the provided roof curb gasket seal.

Cambridge Air Solutions. 10 Spec Air Series Technical Manual
HIGH PRESSURE REGULATOR ASSEMBLY (HPR)
TYP, IF REQUIRED
A
B
DETAIL A
CONTROL WIRING
(BY OTHERS)
TO RCS
INCOMING POWER
(BY OTHERS)
MANUAL SHUT-OFF VALVE
TO INCOMING GAS SUPPLY
WITH SEDIMENT TRAP
VIA HPR ASSEMBLY (IF REQUIRED)
REMOTE CONTROL
STATION (RCS)
CONTROL WIRING
(BY OTHERS) TO
ELECTRICAL
ENCLOSURE
VENT CAP WITH SCREEN
(INSTALL FACE DOWN
MIN 10FT FROM INTAKE)
INLET OUTLET
VENT PIPE (BY OTHERS)
SHUT-OFF VALVE
SUPPLY PRESSURE TAP
ORIFICE
DETAIL B
LIFTING PROVISIONS
TYP EACH CORNER
TYPICAL INSTALLATION
UNIT PREPARATION AND INSTALLATION
V18 - V30
1. Position and install the discharge nozzles
by screwing them onto the bottom of the
discharge duct.
2. Lower the discharge duct through the roof
opening.
3. Use a crane or comparable lifting device
to raise and position the equipment onto
the mounting curb. Use a spreader bar to
prevent damage and connect slings to the
lifting eyes.
4. Caulk all joints of the unit's accessories
installed in the field. Use a clear or gray
silicone caulking to prevent water leaks.
5. Seal all roof penetrations to prevent roof
leaks.

Spec Air Series Technical Manual 11 Cambridge Air Solutions
IMPORTANT
Refer to the unit rating plate for determining
the minimum gas supply pressure for obtaining
the maximum gas capacity for which this unit
is specified. Any field installed components,
including, but not limited to meters, regulators,
pipe elbows , pipe nipples and strainers must
be installed such that the minimum operating
supply pressure for obtaining the maximum gas
capacity is provided.
1. Check with the local utility or gas supplier for
the facility gas supply pressure.
CAUTION:
If the gas supply pressure is in excess of the
maximum standing pressure indicated on
the unit nameplate, a separate positive shut-
off high pressure regulator must be added
upstream of the unit’s individual manual shut-
off valve. This regulator must be vented to the
outside of the building at least 10 feet from
any intake opening. The vent pipe should be
designed to prevent the entry of water, snow,
insects or other foreign material that could
cause blockage. There must be no reduction in
the size of the vent piping. Depending on the
length and the configuration of the vent piping
the pipe size may need to be increased. Refer
to the applicable codes for proper sizing.
WARNING:
The gas and electrical connections must
not penetrate the unit base or mounting
curb. Cambridge Air Solutions recommends
using pitch pockets or roof boots to seal the
penetrations.
2. Properly size the gas supply piping for the rated
capacity, per local codes, and/or the National
Fuel Gas Code, NFPA 54/ANSI Z223.1 or the
CSA B149.1 Installation Code.
3. Make sure the supply piping is free of foreign
matter and purged.
4. Verify that the gas piping, when installed, will
not restrict or block the access door from fully
opening.
5. Install gas piping to the ventilation air unit
in accordance with local codes or, in their
absence, in accordance with the National Fuel
Gas Code, NFPA 54, ANSI Standard Z223.1, or
the CAN/CGA B149 Installation Codes.
IMPORTANT
A 1/8" NPT tap is supplied with the unit for
measuring the gas supply pressure. The tap
is shipped with the low gas pressure shut-off
valve. The valve assembly is shipped loose
and tie wrapped to the gas train, to be field
installed. If the gas supply pressure exceeds that
indicated on the nameplate, the installer must
install a 1/8" NPT tap and high pressure manual
shut-off valve upstream of the high gas pressure
regulator.
IMPORTANT
An adequate sediment trap must be installed
prior to all gas controls for the unit and as
close to the gas inlet connection of the unit as
practical.
Many gas train components are equipped with
listed Vent Limiters as atmospheric bleeds,
however, local codes may require that these
vents and bleeds be vented to the outdoors.
If so, the vent piping should be designed to
prevent the entry of water, snow, insects
or other foreign materials that could cause
blockage.
6. Check for leaks in the supply piping system.
Use liquid gas leak detector. Do NOT use flame.
CAUTION:
If the test pressure is in excess of 1/2 PSIG (3.5
KPA), the unit and its manual shut-off valve must
be disconnected from the gas supply system
during pressure testing. Failure to comply will
void the warranty.
If the test pressure is less than or equal to 1/2
PSIG (3.5 KPA), the unit must be isolated from
the gas supply piping by closing its manual
shut-off valve during pressure testing.
CAUTION:
Do not attempt to start the unit at this time.
Premature start-up can result in damage to
the equipment and components.
INSTALLATION INSTRUCTIONS
GAS PIPING

Cambridge Air Solutions. 12 Spec Air Series Technical Manual
IMPORTANT
Before attempting electrical installation, review
the following instructions and wiring and
connection diagrams to make sure you have a
thorough understanding of what is required.
WARNING:
High voltage electrical input to this equipment
is required. EXTREME caution should be
exercised. This equipment must be electrically
grounded in accordance with local codes or
in accordance with National Electrical Code
NFPA 70.
1. Check the unit nameplate to determine the
voltage and amperage requirements.
CAUTION:
If the supply voltage does not agree with the
nameplate voltage, notify your local agent or
Cambridge Air Solutions’ Customer Service
Group at 800-473-4569.
WARNING:
For roof mounting, the gas and electrical
connections must not penetrate the unit base
or mounting curb. Cambridge Air Solutions
recommends using pitch pockets or roof boots
to seal the penetrations.
2. Wire the supply wiring and adequate Branch
Circuit Protection in accordance with the
National Electrical Code NFPA 70.
3. Mount the Remote Control Station in a location
inside of the building and convenient to the
operator without being susceptible to damage.
4. Space temperature sensors are normally located
along a perimeter wall and out of the direct path
of the discharge air or air infiltration. Consult
the design drawing or your local Cambridge
Air Solutions Representative for placement
assistance. Do not locate the remote mounted
temperature sensors immediately adjacent to
overhead doors because the infiltration air can
affect the sensor when the door is closed and
may not adequately sense the temperature
when the door is open. In dock areas, the sensor
should be located on the first column in from the
outside wall.
IMPORTANT
Observe the special notes and instructions on
the wiring diagrams including the following:
The wiring for the space temperature sensors
must be shielded, twisted-pair wiring and
must be run separately from the other line
voltage AC wiring. This also applies to other
remotely mounted controls utilized in the
Maxitrol 44 control systems. Shielded wire
which is routed to the electrical control
enclosure on the unit should extend beyond
the high voltage section of the enclosure
before the shielding is removed and the wiring
is distributed to its ultimate destination.
Shielding must be grounded on one end only.
IMPORTANT
Conduit connections for power and control
wiring must be caulked to ensure a tight seal and
prevent moisture accumulation.
5. Wire the Remote Control Station and other
temperature control options using Class 2 wiring
per Cambridge Air Solutions wiring diagram
and National Electrical Code Article 725 or local
codes.
6. Run conduit and primary wiring to the
disconnect switch inside of the control enclosure
on the unit per National Electrical Code NFPA
70.
7. Return the wiring diagram to the manual holder.
Replace and fasten all access covers.
CAUTION:
Do not attempt to start the ventilation air unit
at this time.
Premature start-up can result in damage to the
equipment and components.
INSTALLATION INSTRUCTIONS
ELECTRICAL

Spec Air Series Technical Manual 13 Cambridge Air Solutions
START-UP INSTRUCTIONS
1. Visual Inspection Of Equipment
(page 13)
2. Electrical Supply Voltage Verification
(page 13)
3. Gas Supply Pressure Verification
(page 14)
4. Blower Rotation Check
(page 14)
5. Burner Profile Damper Pressure Drop Check
(page 14)
6. Motor Amp Draw Check
(page 15)
7. Calculating and Adjusting
Burner Manifold Pressure
(page 15)
8. Gas Valve Leak Check
(page 16)
9. Gas Train Leak Check
(page 17)
10. Minimum Fire Setting
(page 17)
11. Low Fire Start Adjustment
(page 18)
12. Final Unit Preparation
(page 19)
13. Remote Control Station
Operational Check
(page 19)
After start-up, please complete and fax the Spec
Air Series Start-Up Checklist to the Cambridge
Customer Service Group. Receipt of a completed
checklist will extend the start date for your warranty
period to the date of the start-up but not to exceed
six months from date of shipment.
IMPORTANT
Read the following instructions carefully. Any
unauthorized modifications to, or deviations from
these instructions may void the warranty.
1. VISUAL INSPECTION OF EQUIPMENT
a. Check for any physical damage from shipping
or installation that could render the unit
inoperable.
b. Verify all unit accessories and filters (if
applicable) have been properly installed.
c. Check for loose components (belts, plugs,
terminal screws, etc.).
d. Verify the access doors and controls
enclosure are free from obstructions, such
that they can be fully opened.
e. Verify the field wiring, both primary and
control, has been installed according to the
Cambridge Air Solutions wiring diagram and
the National Electrical Code.
f. Verify that a sediment trap has been provided
upstream of other gas train components.
g. Verify the high pressure regulator and/or vent
limiter, if applicable, have been vented to the
outside of the building at least 10 feet from
any intake opening.
h. Verify the factory supplied manual gas shut-
off cock is installed external to the unit and
downstream of the high pressure regulator, if
applicable.
i. Verify that the gas piping unions are tight.
j. Verify that the burner union is tight.
2. ELECTRICAL SUPPLY VOLTAGE
VERIFICATION
Remove electrical control enclosure access
door and check the electrical supply voltage
at the disconnect switch. For electrical control
enclosure drawings, see page 41.

Cambridge Air Solutions. 14 Spec Air Series Technical Manual
CAUTION:
Do not proceed with start-up unless the
supply voltage agrees with the nameplate
voltage. If the supply voltage does not agree
with the nameplate voltage, check with your
local Cambridge Air Solutions representative
or Cambridge Air Solutions’s Customer
Service Group at 800-473-4569 to determine
what changes are required.
3. GAS SUPPLY PRESSURE VERIFICATION
Verify that the gas supply pressure complies with
the unit nameplate.
CAUTION:
Do not proceed with start-up unless the gas
supply pressure agrees with the nameplate
pressure requirements. If the gas supply
pressure is in excess of the maximum pressure
indicated, a separate positive shut-off high
pressure regulator must be added upstream
of the unit’s low pressure manual shut-off
valve. If a high pressure regulator is needed
and has not been installed, check with your
local Cambridge Air Solutions representative
or Cambridge Air Solutions’ Customer Service
Group at 800-473-4569 to determine the size
and capacity requirements that are required.
4. BLOWER ROTATION CHECK
a. Open the access door on the electrical control
enclosure side and turn the disconnect switch on.
WARNING:
When the disconnect switch is activated with
the enclosure open, live power is present. Only
experienced technicians with knowledge and
respect for live power should proceed beyond
this point.
b. Turn the blower service switch to the “LOCAL”
position. The blower motor will start after the
motorized damper opens. Then turn the blower
service switch to the “OFF”position and verify
the blower is rotating in the proper direction. (See the
directional arrow on the blower housing.)
IMPORTANT
On a three phase system, the rotation direction of
the blower may be reversed by switching any two
wires located on the downstream side of the service
disconnect. The electrical supply to the unit must be
turned off prior to switching the wiring.
IMPORTANT
Indications of loose belts include barking or squealing
when the blower starts. If these symptoms occur,
please refer to the BELT TENSIONING section of the
MAINTENANCE INSTRUCTIONS (page 34). Periodic
belt adjustments may be required.
5. BURNER PROFILE DAMPER PRESSURE DROP
CHECK
IMPORTANT
The blower access doors must be closed when
adjusting the profile plate.
a. Turn the blower service switch to the “LOCAL”
position. (Note: The burner service switch
must remain in the “OFF” position)
b. Check the pressure drop across the burner
with an inclined manometer or similar
differential pressure measuring device (not
provided). The pressure drop across the
burner profile plate shall be 0.68" WC for units
without filters and 0.72" WC for units with
filters.

Spec Air Series Technical Manual 15 Cambridge Air Solutions
c. To change the profile plate pressure drop
on units with a Manual Profile Adjust
mechanism, locate the adjusting mechanism
in the gas train enclosure, loosen the lock-
down bolt, and rotate the hex shaft to
increase or decrease the pressure drop, as
required. Hold the hex shaft and re-tighten
the lock-down bolt to secure the mechanism.
IMPORTANT
Call the Cambridge Air Solutions Customer Service
Group at 800-473-4569 if unable to obtain the
required pressure drop across the burner profile
plate.
6. MOTOR AMP DRAW CHECK
IMPORTANT
The unit access doors must be closed for this test.
a. Check the motor current at the overload relay
on all three legs.
b. Turn the blower service switch to the “OFF”
position.
IMPORTANT
The average amps must not exceed the motor
nameplate FLA. High amperage may indicate
excessive blower RPM. Call the Cambridge Air
Solutions Customer Service Group at 800-473-4569 if
unable to obtain acceptable amperage readings.
7. CALCULATING AND ADJUSTING BURNER
MANIFOLD PRESSURE
a. Turn the disconnect switch off.
b Disconnect #3 wire from the amplifier to drive the
modulating valve to full open and keep the unit in
continuous high fire.
c. If the ambient temperature is at or above
the Entering Air Thermostat (EAT) setpoint
on the multi-functional PC board, then note
the setpoint position and set the EAT to its
highest setting (see page 49). If the ambient
temperature exceeds its highest setting,
remove the set point jumper and rotate 90˚
for the bypass mode.

Cambridge Air Solutions. 16 Spec Air Series Technical Manual
d. Remove the 1/8" NPT plug from the manual
shut-off valve located just prior to the burner
and connect a manometer for the purpose of
measuring the manifold pressure.
e. Refer to the unit nameplate for the Manifold
Differential Pressure (MDP) (inch WC) for
which the unit was specified.
Record the Nameplate Manifold Differential
Pressure
f. Turn the disconnect switch on.
g. Turn the blower service switch to the
“LOCAL”position. The blower motor will
start. Monitor the pressure reading on the
manometer. Record the Manifold Static
Pressure (Blower Only).
h. Using the formula below, calculate the required
manifold pressure:
Nameplate Manifold Differential Pressure
___________inch WC
+ Manifold Static Pressure (Blower Only)
___________inch WC
= Calculated Manifold Pressure
___________inch WC
IMPORTANT
The high limit may trip on warm days. If this occurs
allow the high limit to cool by leaving the blower
only on for 3-5 minutes. Turn the blower and burner
switches to the "OFF" position. Access the high limit
and manually reset. Replace access panels. Turn the
blower and burner switches to the "LOCAL" position.
i. Turn the burner service switch to the “LOCAL”
position. After a delay for pre-purge and igniter
warm-up, the burner will light.
j. Observe the manometer reading and compare
to the Calculated Manifold Pressure above. If
the manifold pressure reading does not equal this
value, adjust the manifold pressure regulator
until the proper manifold pressure is obtained.
See page 39 for gas train drawing.
IMPORTANT
The pressure drop across the burner profile damper
that was adjusted in Step 5 (page 14) must not fall
below 0.51 inches WC for natural gas units and
0.55 inches WC for natural gas with a filter section or
filters in the rainhood. If the pressure drop is below
these values the low airflow switch will shutoff power
to the burner. This is an indication of low airflow or
burner overfiring. To correct this condition, either
adjust the manifold pressure regulator to reduce
the manifold pressure or increase the blower speed,
provided the motor full load amps are not exceeded.
k. Turn the blower and burner service
switches to the “OFF”position, remove the
manometer from the manual shut-off valve,
re-install the 1/8" NPT plug.
8. GAS VALVE LEAK CHECK
All units should be evaluated for the gas
tightness of the gas valve seat. Units are
equipped with a leak test facility to assist in
checking this seal. A momentary switch and a gas
port for measuring pressure between valves are
provided as the leak test hardware (page 40).
Refer to the Individual Component Description
Section (page 49) for more information
regarding the leak test switch. The procedures
for the gas valve leak check are as follows:
a. Connect a 0 to 10 inches water column
(inch WC) manometer to the 1/8" NPT
tapped fitting on the manual shut-off
valve located just prior to the burner for
the purpose of monitoring an increase in
pressure. Verify that the manometer is
properly zeroed.
b. Close the manual burner shut-off valve,
hold the momentary leak test switch in
the closed position, and wait 30 seconds
to read the manometer. If the reading
is greater than 0 inch WC, refer to the
Maintenance Instruction Section for
information on Gas Valve Cleaning (page
33) for cleaning the safety shut-off valve
(SSV) which is closest to the burner and
retest. If the reading is 0 inch WC, remove
the manometer and reinstall the pipe plug.

Spec Air Series Technical Manual 17 Cambridge Air Solutions
c To check the gas tightness of the shut-
off valve (SOV) in the gas train which
is farthest from the burner connect the
manometer to the leak test port between
the valves and verify that the manometer
is properly zeroed. Wait 30 seconds to
read the manometer. If the reading is
greater than 0 inch WC, refer to the
Maintenance Instruction Section (page
32) for information on Gas Valve Cleaning
for the shut-off valve (SOV) gas valve and
retest. If the reading is 0 inch WC, remove
the manometer and reinstall the pipe plug.
9. GAS TRAIN LEAK CHECK
a. Turn the blower and burner service
switches to the “LOCAL”position.
b. With the burner operating, spray the
complete gas train with leak detector
solution, checking all pipe connections and
plugs.
c. Turn the blower and burner service
switches to the “OFF”position.
WARNING:
Do not use flame to leak check piping.
WARNING:
Any gas leak detected must be repaired before
the ventilation air unit is placed into service.
10. MINIMUM FIRE SETTING
IMPORTANT
All access doors must be closed during this
procedure.
a. For units with an A1044 amplifier: Reinstall
#3 wire on the amplifier that was removed
in Step 7.b. (See page 15).
b. Connect a meter set to read DC
microamps (mA) in order to verify the
minimum fire flame signal during the
adjustment process. Connect the meter
by removing the red wire from terminal
FP of the flame safeguard relay (FSR) and
attaching the positive lead of the meter to
terminal FP and the negative lead to the
red wire.
c. Turn the blower and burner switches to
the “LOCAL” position.
d. After the burner has ignited, remove the
#8 wire from the amplifier to drive the
modulating valve to minimum fire.
e. Look through the burner viewport in the
front of the unit to verify that the burner
flame is a very small ribbon (approximately
1-1/2" to 2" long) that is
evenly spread across the
burner (without gaps).
f. Verify that the minimum fire flame signal is
steady and above 2.0 microamps (mA).

Cambridge Air Solutions. 18 Spec Air Series Technical Manual
IMPORTANT
If any of the conditions in steps 10.e and 10. f are not
met, an adjustment is required.
g. Minimum Fire Adjustment
i. On M611 modulating valves, to adjust
the minimum fire, remove cap (A)
exposing the minimum fire adjusting
screw. On the MR212 modulating/
regulating valve, remove the housing
cover, then cap (A), and then loosen
lock screw (C). Turn the adjusting screw
(B) to obtain the desired minimum fire
setting. A clockwise rotation decreases
the flame size and reduces minimum
flow rate. Repeat steps 10.e and 10.f.
Modulator
ii. Replace the cap (A). Tighten the lock
screw (C) on the MR212 valve prior to
reinstalling the cap and housing cover.
iii. Turn the blower and burner service
switches to the “OFF”position.
iv. Reinstall the #8 wire on the amplifier
that was removed in Step 10.d. (See
page 17).
v. Remove the meter and reattach the red
wire to terminal FP on the FSR board.
11. LOW FIRE START ADJUSTMENT
The Low Fire Start control setting is preset at
the factory to provide a fixed, repetitive, initial
firing rate that equates to the following for most
burner applications:
• 20˚F to 30˚F temperature rise
• 0.10 to 0.30 inches WC manifold differential
pressure (above blower pressure)
• Voltage to the modulating valve of 9 to 11 Volts
DC for the M611 valve and 10 to 13 Volts DC for
the Maxitrol MR212 valve.
• Flame length of 3" to 5"
The Low Fire Start function lasts for 15 seconds
before returning to the control of the temperature
control system. It is important that the flame
travels across the burner length fast enough
(within 2 seconds) to establish the flame signal
during the trial for ignition period. If adjustment is
required, proceed as follows:
a. Connect a meter in the flame sense circuit
as in step 10.b (page 17).
b. Connect a manometer to the burner static
pressure port. Turn the blower service
switch to the “LOCAL” position and the
burner service switch to the “OFF” position
and measure the burner static pressure.
c. Connect a DC voltmeter to terminals “MV
OUT” on the multi-functional PC board.
d. Turn the burner service switch to the
“LOCAL”position and monitor the
modulating valve voltage, flame length,
manifold differential pressure, and the time
required to establish flame signal after the
gas valves are energized. (This may need
to be repeated several times to note all of
the above information)
e. If adjustment is required, the Low Fire
Start adjustment screw is located on the
multi-functional PC board as shown in
the drawing. Only minor adjustments are
normally required to obtain the proper
setting.