Lennox G20RE Series User manual

SERVICE G20RE
UNIT
INFORMATION
Page 1 1994 Lennox Industries Inc.
Corp. 9419 – L9 Litho U.S.A.
G20RE SERIES UNITS
I – INTRODUCTION
G20RE and G20RXE series units are mid–efficiency
downflow gas furnaces with Duracurveheat ex-
changers formed of aluminized steel. G20RE units
come in heating capacities of 50,000 to 150,000 Btuh. In
cooling applications, blowers are equipped to handle
up to 5 tons of cooling capacity. Refer to Engineering
Handbook for proper sizing.
Units are factory supplied for use with natural gas. A
conversion kit to LPG operation is available for the
G20RE only. All units are equipped with an electronic
ignition. G20RXE models meet the California Nitrogen
Oxides (NOx) Standards and California Seasonal Effi-
ciency requirements. All units use a redundant gas
valve to assure safety shut–off as required by A.G.A.
Featured on G20RE series is a burner box damper as-
sembly located on the intake side of the burners. A
damper door in the burner box shuts during unit off
cycles to retain heat in the unit. A damper prove switch
ensures that damper is open before gas valve is ener-
gized. Since the G20RE furnaces have atmospheric
burners there is no induced draft motor. All G20RE
units have a draft diverter which allows the use of stan-
dard single wall vent connectors.
SPECIFICATIONS (continued on next page)
Model No.
Input Btuh
Output Btuh
*A.F.U.E.
Flue connection (in. diameter)
Temperature rise range
High static certified by A.G.A.(in wg.)
Gas piping size
I.P.S. (in.)
Blower wheel nominal diameter x width (in.)
Blower motor hp.
Electrical characteristics
Natural
**LPG
G20RQ2/3E-50 G20RQ3E–75 G20RQ4E-75 G20RQ3/4E-100
50,000
40,000
78.0%
4 Round
20-50
.50
1/2
1/2
10 x 8
1/3
2, 2–1/2 or 3Tons of cooling (add–on)
58,000
78.0% 78.0% 78.0%
75,000
59,000
75,000
79,000
4 Round 4 Round 5 Oval
50-80 30-60 50-80
.50 .50 .50
1/2
1/2
1/2
1/2
1/2
1/2
10 x 8 11 x 9 11 x 9
1/3 1/2 1/2
*Annual Fuel Utilization Efficiency based on D.O.E. test procedures and according to F.T.C. labeling requirements.
Isolated combustion system rating for non–weatherized furnaces.
•G20RQ2/3XE-50 •G20RQ3XE–75 •G20RQ4XE-75 •G20RQ3/4XE-100
100,000
California Seasonal Efficiency– “X” Models 72.1% 74.8% 72.0% 74.5%
Number and Size of Filters (in.) (2) 20 x 10 x 1 (2) 20 x 10 x 1 (2) 20 x 12 x 1 (2) 20 x 12 x 1
2, 2–1/2 or 3 3, 3–1/2 or 4 3, 3–1/2 or 4
•Not Available with LPG.
**LPG kit must be ordered extra for field changeover.
120 volts — 60 hertz — 1 phase (less than 12 amps) — All Models

Page 2
Model No.
Input Btuh
Output Btuh
*A.F.U.E.
Flue connection (in. diameter)
Temperature rise range
High static certified by A.G.A.(in wg.)
Gas piping size
I.P.S. (in.)
Blower wheel nominal diameter x width (in.)
Blower motor hp.
Electrical characteristics
Natural
**LPG
G20RQ5E-100 G20RQ3E–125 G20RQ4/5E-125 G20RQ4/5E-150
100,000
77,000
78.0%
5 Oval
40-70
.50
1/2
1/2
12 x 12
3/4
120 volts — 60 hertz — 1 phase (less than 12 amps) — All Models
4, 4–1/2 or 5Tons of cooling (add–on)
98,000
78.0% 78.0% 78.0%
125,000
99,000
125,000
118,000
5 Oval 5 Oval 6 Oval
70-100 50-80 55-85
.50 .50 .50
1/2
1/2
1/2
1/2
1/2
1/2
10 x 8 12 x 12 12 x 12
1/3 3/4 3/4
*Annual Fuel Utilization Efficiency based on D.O.E. test procedures and according to F.T.C. labeling requirements.
Isolated combustion system rating for non–weatherized furnaces.
•G20RQ5XE-100 •G20RQ3XE–125 •G20RQ4/5XE-125
150,000
California Seasonal Efficiency– “X” Models 74.7% 75.6% 74.4% -––––
Number and Size of Filters (in.) (2) 20 x 14 x 1 (2) 20 x 14 x 1 (2) 20 x 14 x 1 (2) 20 x 16 x 1
2, 2–1/2 or 3 4, 4–1/2 or 5 4, 4–1/2 or 5
•Not Available with LPG.
**LPG kit must be ordered extra for field changeover.
SPECIFICATIONS (continued from previous page)
PILOT/ELECTRODE
ASSEMBLY
PARTS IDENTIFICATION (G20RE)
HEAT
EXCHANGER
DRAFT
HOOD
UPPER ACCESS PANEL
BURNERS
BURNER
BOX IGNITION
CONTROL
GAS
MANIFOLD
BURNER BOX DAMPER ASSEMBLY
PRIMARY
LIMIT
CONTROL
CABINET
ROLL–OUT
SWITCH
VENT SAFETY
SHUT–OFF
SWITCH
GAS
VALVE
FLUE TRANSITION
LOWER
ACCESS
PANEL
FILTER ACCESS
DOOR
DOOR
INTERLOCK
SWITCH
BCC2
CONTROL
REMOVABLE
STRIP
..
LEFT SIDE VIEW
BURNER BOX
FIGURE 1
DAMPER PROVE
SWITCH (S64)
RETURN
SPRING
DOOR
PATCH
PLATE
AXLE
FILTERS

Page 3
II – UNIT COMPONENTS
G20RE unit components are shown in figure 1. The
blower controls can be accessed by removing the up-
per access panel. Gas valve and burners can be ac-
cessed by removing the lower access panel.
A – Control Box Components
The G20RE control box is shown in figure 2. It is located
behind the lower access panel between the draft hood
and the gas valve. The control box can be accessed by
loosening the top screw and removing the bottom
screw. The control box cover can then be rotated from
the control box. The control box houses the (T1) Trans-
former and serves as a make-up box for low voltage
field wiring. It also contains a grounding lug for the
unit.
G20RE CONTROL BOX - FRONT VIEW
FIGURE 2
CONTROL TRANSFORMER
(T1)
GROUNDING SCREW
1 – Control Transformer (T1)
All G20RE series units use a single line voltage
(120VAC) to 24VAC transformer. It is located inside the
control box providing power to the low voltage section
of the unit.
B – BCC2-2 Blower Control (A15)
All G20RE units utilize a BCC2-2 blower control as illus-
trated in figure 3. It is located behind the upper access
panel on the BCC2-2 blower control panel. The BCC2-2
is a printed circuit board which controls the blower and
monitors primary limit and gas valve operation. The
control has a non–adjustable, factory preset “on” fan
timing. Fan “off” timings are adjustable. The board is
divided into two sections, 120VAC and 24VAC.
“CAB” and “XFMR ” send 120VAC to the damper mo-
tor and transformer, respectively. Active cooling and
heating blower speed terminals and three dummy “D”
terminals are located on the 120VAC side of the
BCC2-2. The “CF” terminal is used for wiring in the op-
tional continuous fan kit. Also located on this side of
the control are neutral terminals and a terminal for ac-
cessories such as an electronic air cleaner.
24VAC from transformer T1 is supplied to terminal
“24V” on the 24VAC side of the BCC2-2. Thermostat
connections and safety circuit terminals are also lo-
cated on the 24VAC side of the control. Fan “off” tim-
ings may be adjusted by changing the position of a
jumper across terminal pins.
XFMRN
HSIN
120VAC OUTPUT
COOLING SPEED TAP TERMINAL
120VAC OUTPUT HEATING
SPEED TAP TERMINAL
120VAC COMMON
G20RE BLOWER CONTROL CENTER
INB
N1
CABN
CAB
L1
A
XFMR
D
D
D
H
ACC
120VAC OUTPUT SWITCHED
ACCESSORY TERMINAL
BLOWER TIME ADJUSTMENT
JUMPER
V
LIMIT W WR YTG
210
270
90
150
24V T COM
CF
120VAC OUTPUT
CONTINUOUS FAN TERMINAL
INSULATED COVER
THERMOSTAT
120VAC INPUT LINE VOLTAGE
120VAC OUTPUT TO DAMPER
DOOR
24VAC COMMON TO TRANSFORMER
120VAC OUTPUT TO TRANSFORMER
DUMMY TERMINAL (NO VOLTAGE)
24VAC COMMON
TO THERMOSTAT
24VAC POWER INPUT
24VAC OUTPUT
THROUGH LIMITS TO IGNITION
CONTROL
24VAC INPUT FROM PRIMARY LIMIT
24VAC INPUT FROM IGNITION
CONTROL SENSING CIRCUIT
120VAC COMMON
FIGURE 3
DUMMY TERMINAL (NO VOLTAGE)
CONNECTIONS

Page 4
C – Blower Motors and Capacitors
All G20RE units use direct drive blower motors. All mo-
tors used are 120V permanent split capacitor motors to
ensure maximum efficiency. See table1 for ratings.
TABLE 1
G20R BLOWER RATINGS 120V 1PH
BLOWER MOTOR HP
Q2/3, Q3
Q4, Q3/4
Q5, Q4/5
CAP
3/4
1/2
1/3 5MFD 370V
7.5MFD 370V
40MFD 370V
D – Door Interlock Switch (S51)
A door interlock switch rated 16A at 125VAC is located
behind the BCC2-2 blower control panel. The switch is
wired in series with line voltage. When the blower door
access panel is removed the unit will shut down.
E – Blocked Vent Switch (S62)
The blocked vent switch (S62) is located on the right
side of the draft diverter. The switch is a high temper-
ature N.C. SPST manual-reset limit connected in se-
ries with the ignition control A3. It trips when there is
excess heat in the draft diverter or improper venting.
The switch is factory set at 300 °+12°(149°C) and
cannot be adjusted.
F – Flame Rollout Switch (S47)
Flame rollout switch is a high temperature limit located
on top of the burner box. The limit is a N.C. SPST manu-
al-reset limit connected in series with the ignition con-
trol A3. When S47 senses rollout, the ignition control
immediately stops ignition and closes the gas valve. If
unit is running and flame rollout is detected, the gas
valve will close and ignition control will be disabled.
The switch is factory set and cannot be adjusted. See
table 2. The switch can be manually reset.
TABLE 2
FLAME ROLLOUT SWITCH SETPOINTS
HEATING INPUT KBTUH SETPOINT
50, 75
100, 125, 150
260°F + 12°F
300°F + 12°F
G – Primary Limit Control (S10)
The primary limit switch (S10) on all units is located in
the middle of the heating vestibule wall.
G20RQ2/3(X)E-50, Q3(X)E-75, Q4(X)E-75, Q3/4(X)E-100
and Q3(X)E-125 units use a SPST self resetting limit.
See figure 4. When excess heat is sensed in the heat ex-
changer, the limit switch will open and interrupt the
current to the gas valve. If the limit is tripped, BCC2-2
energizes the blower. The limit automatically resets
when unit temperature drops below the reset point.
See table 3.
INSULATING COVER (s)
FIGURE 4
G20RQ2/3(X)E-50
Q3(X)E-75
Q3(X)E-125
Q3/4(X)E-100
LIMIT CONTROL FOR:
SPADE CONNECTORS
INSULATING COVER
LIMIT
LIMIT
Q4(X)E-75
All other units use a fan control-type limit shown in fig-
ure 5. It is used to protect the unit from high tempera-
tures. The blower limit is a resistive-type bimetal SPST
automatic resetting switch. This control does not con-
tain a fan control. The control is factory preset and is
not adjustable. See table 3.
PRIMARY LIMIT TEMPERATURES
Series
Series
TABLE 3
UNIT MODEL NO. TEMP. RISE TEMP. FALL
G20RQ2/3(X)E–50
G20RQ3(X)E–75
Series
Series 230°F + 5°F 200°F + 8°F
G20RQ3/4(X)E–100
G20RQ5(X)E–100
Series
Series
G20RQ3(X)E–125
G20RQ4/5(X)E–125
G20RQ4/5(X)E–150
Series
190°F + 10°F –5°F160°F + 10°F
220°F + 10°F250°F + 6°F
150°F + 15°F
180°F + 15°F
150°F + 15°F
180°F + 15°F
G20RQ4(X)E–75 Series
FIGURE 5
HONEYWELL LIMIT CONTROL FOR:
LIMIT SETTING
POINTER
FIXED STOP
G20RQ5(X)E–100
G20RQ4/5(X)E–12
5
G20RQ4/5(X)E–150
NOTE: This control
is actuated by a bi-met-
al coil and does not
contain a fan contol.
NOTE: Do not attempt
to adjust this limit.

Page 5
H – Secondary Limit (S21)
The secondary limit switch (S21) is a high temperature
limit located on the left side of the blower scroll. The
limit is a N.C. SPST auto-reset limit connected in series
with the ignition control A3. The switch is similar in de-
sign to the primary limit control. See figure 4. The limit
detects heat in the blower compartment indicating a
possible fan failure. When S21 senses heat, the igni-
tion control immediately stops ignition and closes the
gas valve. If unit is running and heat is detected, the
gas valve will close and ignition control will be dis-
abled. The switch is factory set and cannot be ad-
justed. See table 4. The switch automatically resets.
Series
Series
G20RQ4/5(X)E–125
G20RQ4/5(X)E–150
SECONDARY LIMIT TEMPERATURES
TABLE 4
UNIT MODEL NO. TEMP. RISE TEMP. FALL
G20RQ2/3(X)E–50
G20RQ3(X)E–75
Series
Series 140°F + 5°F 110°F + 10°F
G20RQ3/4(X)E–100
G20RQ5(X)E–100
Series
Series
G20RQ3(X)E–125 Series
130°F + 5°F 100°F + 10°F
G20RQ4(X)E–75 Series
120°F + 5°F90°F + 10°F
130°F + 5°F 100°F + 10°F
140°F + 5°F 110°F + 10°F
I – Gas Valve (Figure 6)
All G20RE units use a Robertshaw gas valve. All gas
valves are internally redundant to assure safety shut–
off. If the gas valve must be replaced, the same type
valve must be used.
INLET
PRESSURE
TAP
ON
OFF
FIGURE 6
ROBERTSHAW 7100 GAS VALVE
GAS VALVE KNOB SHOWN IN OFF POSITION
PCM
PRESSURE REGULATOR
ADJUSTMENT SCREW
TOP VIEW
FRONT
VIEW
PILOT ADJUSTMENT SCREW
VALVE
INLET VALVE
OUTLET
OUTLET
PRESSURE
TAP
J – Electronic Ignition Control (Figure 7)
The Robertshaw electronic ignition control (A3) is an
intermittent ignition control module located on the
vestibule panel. See figure 1. When there is a call for
heat, the control generates a spark to ignite the pilot,
after which the control senses the flame. If the flame
current is too weak (less than 1 microamp) the control
will shut down and de–energize the gas valve. Flame
current should be between 1 and 5 microamps.
DANGER
Shock Hazard.
Spark related components con-
tain high voltage. Disconnect
power before servicing unit. The
ignition control is not field repair-
able.
Can cause unsafe operation, inju-
ry or death.
The 24VAC terminals and the gas knob are located on
top of the valve. All terminals on the gas valve are con-
nected to wires from the electronic ignition control.
The left red wire to terminal “P” energizes the pilot
valve. An orange sensing wire from terminal
“V”(marked VALVE SENSE) of the BCC2-2 control rides
“piggy back” on the “P” terminal connection. The
main valve, terminal “M,” is energized by the right red
wire. The blue wire, terminal “C,” is the common for
the gas valve.
ROBERTSHAW IGNITION CONTROL
FIGURE 7
MV/PV – MAIN AND PILOT VALVE COMMON
MV – 24VAC OUTPUT TO MAIN VALVE
PV – 24VAC OUTPUT TO PILOT
TH – 24VAC INPUT FROM BCC2-2 THROUGH LIMITS
SENSE – MICROAMP SIGNAL FROM FLAME SENSOR
TR – 24VAC COMMON
IGN – HIGH VOLTAGE TO SPARK IGNITOR
TRIGN SENSE TH MV MV/PVPV

Page 6
K – Pilot Tube, Ignition Wire and Flame Rod
The pilot tube from the gas valve and the flame sensor
and ignition wires from the electronic ignition control
enter through the top of the burner box to the pilot
burner assembly.
Figure 8 shows the clearance between top of the pilot
burner head and the top of the main burner surface.
IGNITION
WIRE
FLAME SENSOR
WIRE
PILOT ASSEMBLY
5/16”
PILOT
HEAD
FIGURE 8
BURNER
SURFACE
L – Burner Box/Damper Door
The damper motor is located on the right side of the
burner box. On the left side of the burner box, behind a
protective plate is the damper prove switch. Refer to
figure 9. The burner box top is removable on all units.
When there is a call for heat, the damper motor is ener-
gized and damper door opens as the damper motor
axle begins to rotate.
REMOVEABLE
TOP
DAMPER MOTOR/GEAR
PATCH PLATE
PATCH PLATE
SPRING
DAMPER
PROVE SWITCH
PROVE
SWITCH COVER
OBSERVATION PORT
COVER
DAMPER
PILOT PATCH
PLATE
DAMPER
BOX
DAMPER BOX PARTS ARRANGEMENT
(G20RE Units Shown)
DAMPER OPENING
FIGURE 9
ROLL–OUT
SWITCH
M – Damper Prove Switch (S64)
The spring, which is held by a notch in the burner box
frame, activates the damper prove switch as the damp-
er door opens. See figure 10. The axle rotates the
damper door to open position. As the axle turns, the
spring winds backward to make contact with the damp-
er prove switch. The protective cover plate is remov-
able (one screw) and the spring may be unclipped for
service to the damper door or burner box. Spring must
be removed in order to remove the damper door.
After service is complete, the spring must rest snugly
in notch for damper prove switch to function properly.
Do not force door open, damage to the spring and mo-
tor may occur. Take care to open damper door slowly.
Axle rotates
and opens the
door, slot in left
end of axle
pulls spring
back to activate
damper prove
switch.
DAMPER
PROVE
SWITCH
SPRING SPRING FITS
SNUGLY IN NOTCH
FIGURE 10
AXLE
DAMPER
DOOR
DAMPER PROVE SWITCH ASSEMBLY
MANIFOLD
III – PLACEMENT AND INSTALLATION
Make sure the unit is installed in accordance with
installation instructions and all applicable codes.
IV – START-UP
A – Preliminary and Seasonal Checks
1 – Inspect electrical wiring, both field and factory
installed for loose connections. Tighten as re-
quired.
2 – Check voltage at disconnect switch. Voltage must
be within range listed on the nameplate. If not, con-
sult the power company and have voltage condi-
tion corrected before starting unit.

Page 7
B – Heating Start-Up
WARNING
Shock and burn hazard.
G20RE and G20RXE units are equipped with an in-
termittent pilot ignition system. Do not attempt
to light manually.
1 – Set thermostat to OFF position. Close manual knob
on gas valve.
2 – Wait 5 minutes.
3 – Open manual knob on gas valve, replace burner ac-
cess door and turn on unit electrical supply.
4 – Set fan switch to AUTO or ON and move system
selection switch to HEAT. Adjust thermostat to a
setting above room temperature.
5 – If unit does not light the first time, it will attempt
one more ignition before locking out.
6 – If lockout occurs, repeat steps 1, 2, 3 and 4.
C – Safety or Emergency Shutdown
Turn off power to unit. Close manual and/or main gas
valves.
D – Extended Period Shutdown
Turn off thermostat or set to “UNOCCUPIED” mode.
Close all gas valves (both internal and external to unit)
to guarantee no gas leak into combustion chamber.
Turn off power to unit. All access panels, covers and
vent caps must be in place and secured.
V – HEATING SYSTEM SERVICE CHECKS
A – A.G.A. Applications and Requirements
All units are A.G.A. design certified without modifica-
tions. Refer to the G20RE Operation and Installation
Instruction Manual Information.
B – Gas Piping
Gas supply piping should not allow more than
0.5”W.C. drop in pressure between gas meter and unit.
Supply gas pipe must not be smaller than unit gas con-
nection.
Compounds used on gas piping threaded joints should
be resistant to action of liquefied petroleum gases.
C – Testing Gas Piping
IMPORTANT
In case emergency shutdown is required, turn off
the main shut-off valve and disconnect the main
power to unit. These controls should be properly
labeled by the installer.
When pressure testing gas lines, the gas valve must be
disconnected and isolated. Gas valves can be dam-
aged if subjected to more than 0.5psig (14” W.C.). See
figure 11
. If the pressure is equal to or less than 0.5psig
(14”W.C.), use the manual shut–off valve before pres-
sure testing to isolate furnace from gas supply.
FIGURE 11
MANUAL MAIN SHUT–OFF VALVE
WILL NOT HOLD TEST PRESSURE
IN EXCESS OF 0.5 PSIG (14”W.C.)
GAS VALVE CAP
GAS PIPING TEST PROCEDURE
FIELD PROVIDED
LINE PRESSURE TAP
When checking piping connections for gas leaks, use
preferred means. Kitchen detergents can cause harm-
ful corrosion on various metals used in gas piping. Use
of a specialty Gas Leak Detector is strongly recom-
mended. It is available through Lennox under part
number 31B2001. See Corp. 8411–L10, for further de-
tails.
Do not use matches, candles, flame or any other source
of ignition to check for gas leaks.
D – Testing Gas Supply Pressure
When testing supply gas pressure, connect test gauge
to inlet pressure tap (field provided). See figure 11. Test
supply gas pressure. Low pressure may result in erratic
operation or underfire. High pressure can result in per-
manent damage to gas valve or overfire. For natural
gas units, operating pressure at unit gas connection
must be between 4.5” W.C. and 10.5” W.C. For L.P. gas
units, operating pressure at unit gas connection must
be between 10.5” W.C. and 13.5” W.C.
On multiple unit installations, each unit should be
checked separately, with and without units operating.
Supply pressure must fall within range listed in pre-
vious paragraph.

Page 8
E – Check Manifold Pressure
After line pressure has been checked and adjusted,
check manifold pressure. Move pressure gauge to out-
let pressure tap located on unit gas valve (GV1). See
figure 6 for location of pressure tap on gas valve.
IMPORTANT
For safety, connect a shut-off valve between the
manometer and the gas tap to permit shut off of
gas pressure to the manometer.
The gas valve is factory set and should not require ad-
justment. All gas valves are factory regulated. See
table 5 . See tables 6 and 7 for derated manifold pres-
sure values in high altitude application for natural and
LP gases.
Operating Pressure (outlet) in. W.C.
TABLE 5
GAS VALVE REGULATION
3.5 +0 –0.3Natural
L.P. 9.5 + 0.5
Unit (Fuel)
Manifold Adjustment Procedure:
1 – Connect a test gauge to outlet pressure tap on gas
valve. Start unit and allow 5 minutes for unit to
reach high fire steady state.
2 – While waiting for the unit to stabilize, notice the
flame. Flame should be stable and should not lift
from burner. Natural gas should burn blue. L.P. gas
should burn mostly blue with some orange
streaks.
3 – After allowing unit to stabilize for 5 minutes, re-
cord manifold pressure and compare to values
given in table 5.
NOTE– Disconnect heating demand as soon as an
accurate reading has been obtained.
F – Proper Gas Flow
To check for proper gas flow to combustion chamber,
determine Btuh input from unit rating plate or table or
the specifications tables on pages 1 and 2. Divide input
rating by Btuh per cubic foot of available gas. Result is
the number of cubic feet per hour required. Determine
flow of gas through gas meter for two minutes . Multi-
ply by 30 to get hourly flow of gas to burner.
NOTE– To obtain accurate reading, shut off all other
gas appliances connected to meter.
G – High Altitude Derate
C.G.A. certified units used in high altitude applications
are factory equipped with modifications that eliminate
the need for manifold pressure adjustment to obtain
proper heat input. Check the unit rating plate to make
sure unit is a high altitude unit.
A.G.A. certified units must be derated when installed at
an elevation of 2,000 ft. (610 m) or more above sea lev-
el. Tables 6 and 7 show the derated manifold pressure
for high altitude operation with both natural and LP/
Propane gas. Operating this appliance at the manifold
pressure specified on the tables will ensure proper unit
heat input at high altitude. Consult your gas utility for
the local natural gas heating value.
NOTE–This is the only permissible field derate for
this appliance.
2.25” wc
Altitude *Heating Value (Btu/Ft#)
(Ft.) 900 950 1000 1050 1100
0
1000
2000
3000
4000
5000
6000
4.32” wc
4.32” wc
3.65” wc
3.35” wc
3.05” wc
2.77” wc
2.50” wc
3.88” wc
3.88” wc
3.30” wc
3.00” wc
2.75” wc
2.48” wc
3.50” wc
3.50” wc
2.95” wc
2.70” wc
2.45” wc
2.25” wc
3.17” wc
3.17” wc
2.70” wc
2.45” wc
2.25” wc
2.89” wc
2.89” wc
2.45” wc
2.25” wc
HIGH ALTITUDE MANIFOLD PRESSURE
DERATE FOR NATURAL GAS UNITS
*Heating value based on atmospheric pressure of 30” mercury
and temperature of 60
° F (16 ° C).
TABLE 6
_ _ _ _ _ _
_ _
_ _
_ _
ALTITUDE
(Ft.)
MANIFOLD
PRESSURE
HIGH ALTITUDE MANIFOLD PRESSURE
DERATE FOR LP/PROPANE GAS UNITS
0 1000 2000 3000 4000 5000 6000
9.5”
w.c.
8.0”
w.c.
7.2”
w.c.
6.5”
w.c.
5.9”
w.c.
5.3”
w.c.
TABLE 7
9.5”
w.c.
IMPORTANT
For safety, shut unit off and remove manometer as
soon as an accurate reading has been obtained.
Take care to replace pressure tap plug.
H – Flame Signal
Flame signal or microamp is an electrical current which
passes from the ignition control through the sensor
electrode during unit operation. Current passes from
the sensor through the flame to ground to complete a
safety circuit. A 50 microamp DC meter is needed to
check flame signal on the primary ignition control.

FIGURE 13
STATIC PRESSURE
TEST
MANOMETER
G20RE
UNIT
Page 9
To Measure Flame Signal:
1 – Place meter in series between ignition control and
sensor wire. Connect the positive (+) lead of meter
to the ignition control sensor connection and the
negative (–) lead of the meter to the sensor wire.
See figure 12.
2 – Set thermostat for a heating demand and check
flame signal with unit operating. For G20RE series,
a reading of 1 to 5 microamps DC should occur.
Flame signal may rise above 1 to 5 microamps for the
first few seconds after ignition and then level off.
WARNING
Fire and explosion hazard.
These instructions MUST be followed exactly.
Can cause a fire or explosion resulting in property
damage, personal injury or loss of life.
FLAME SIGNAL TEST
FIGURE 12
IGNITION
CONTROL
“SENSE” TERMINAL
SENSOR
WIRE
D.C.
MICROAMP
METER
FLAME SENSOR
VI – BLOWER OPERATION/ADJUSTMENT
NOTE– The following is a generalized procedure
and does not apply to all thermostat controls.
A – Blower operation is dependent on thermostat con-
trol system.
1 – Generally, blower operation is set at thermostat
subbase fan switch. With fan switch in ON position,
blower operates continuously. With fan switch in
AUTO position, blower cycles with demand or runs
continuously while heating or cooling circuit
cycles.
2 – In all cases, blower and entire unit will be off when
the system switch is in OFF position.
B – Temperature Rise
Temperature rise for G20RE units depends on unit out-
put, blower speed and static pressure of the unit setup.
Blower speed must be set for unit operation within
range of “AIR TEMP. RISE °F” listed on the unit rating
plate.
To Measure Temperature Rise:
1 – Place plenum thermometers in the supply and re-
turn air plenums. Locate thermometers in the first
horizontal run of the warm air plenum where it will
not pick up radiant heat from the heat exchanger.
2 – Set thermostat to highest setting.
3 – After plenum thermometers have reached their
highest and steadiest readings, subtract the two
readings. The difference should be in the range
listed on the unit rating plate. If the temperature is
too low, decrease blower speed. If temperature is
too high, first check the firing rate. Provided the fir-
ing rate is acceptable, increase blower speed to re-
duce temperature. To change blower speed taps
see the Blower Speed Taps section in this manual.
C – Discharge Static Pressure
1 – Measure tap locations as shown in figure 13.
2 – Punch a 1/4” diameter
hole in supply and return
air plenums. Insert ma-
nometer hose flush with
inside edge of hole or in-
sulation. Seal around the
hose with permagum.
Connect the zero end of
the manometer to the dis-
charge (supply) side of
the system. On ducted systems, connect the other
end of manometer to the return duct as above. For
systems with non–ducted returns, leave the other
end of the manometer open to the atmosphere.
3 – With only the blower motor running and the evap-
orator coil dry, observe the manometer reading.
Adjust blower motor speed to deliver the required
amount of air.
4 – Discharge static pressure drop must not be more
than 0.5” W.C.
5 – Seal around the hole when the check is complete.

Page 10
D – Blower Speed Taps
Blower speed tap selection is accomplished by chang-
ing the taps at the harness connector at the blower mo-
tor. Disconnect harness connector from motor to ex-
pose speed selectors. Blower speed selections are
listed in table 8.
To Change Blower Speed:
1 – Turn off electric power to furnace.
2 – Remove upper access panel and filter access door.
See figure 1.
3 – Lift left side filter over left support angle. For easy
handling, hold filter at center bottom.
4 – Rotate filter sideways and pull it through the blow-
er access panel opening.
5 – Pull the second filter out the same way as the first.
6 – Grasp blower motor harness connector located on
back on motor. Depress lock tab and pull connector
from motor.
7 – Pull harness connector and wires through blower
access panel opening.
8 – Select desired speeds for heating and cooling.
(Red = heating, Black = cooling, White = common).
See table 8.
BLOWER SPEED SELECTION
G20RQ3/4(X)E–100
G20RQ2/3(X)E–50*
G20RQ3(X)E–75
G20RQ5(X)E–100
G20RQ3(X)E–125
G20RQ4/5(X)E–125
G20RQ4/5(X)E–150
G20RQ4(X)E–75
UNIT
Factory Con-
nected
Speed Taps
Motor Speeds
Available
Cool Heat
24 4
25 4
24 4
24 4
24 4
36 5
36 5
36 5
*DO NOT USE LOW SPEED TAP ON Q2/3–50
BLOWER SPEED SELECTION
HI LOW
2345
23456
SPEED
TAPS
4
5
TABLE 8
◊
◊
◊
MOTOR PLUG SPEED TAP DESIGNATION
9 – Depress harness connector tab to release wire ter-
minal. Select connector location for new speed (re-
fer to unit wiring diagram). Insert wire terminal un-
til it is securely in place. See figure 14.
10 – Replace harness connector to motor .
FIGURE 14
BLOWER SPEED TAP SELECTION
HARNESS
CONNECTOR
MOTOR
DEPRESS TAB TO RELEASE
WIRE TERMINAL. SELECT
CONNECTOR LOCATION
FOR NEW SPEED (REFER TO
UNIT WIRING DIAGRAM).
INSERT WIRE UNTIL IT IS SE-
CURELY IN PLACE.
E – Fan Timings
Fan “off” timings (time that the blower operates after
the heat demand has been satisfied) are determined by
the arrangement of a jumper across pins on the BCC2-2
blower control board. See figure 3. To adjust fan “off ”
timings, gently disconnect jumper and re-position
across pins corresponding with new timing. Fan “on”
time is factory set at 45 seconds and is not adjustable.
WARNING
Shock hazard.
Make sure to disconnect power before changing
fan “OFF” timings.
Can cause personal injury.