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position. Figure 10 shows the various fan off timings
and how switches should be positioned. Unit is shipped
with a factory fan off setting of 180 seconds. Fan off
time will affect comfort and efficiency and is adjustable
to satisfy individual applications. The fan off timing is
initiated after a heating or cooling demand but not after a
blower demand (that is, when indoor thermostat switch
is changed from ON to AUTO and heating/cooling de-
mand is not present, the blower stops immediately).
TABLE 6
FURNACE CONTROL A3 TERMINAL DESIGNATIONS
Terminal
Type
Function
24VAC HOT
1/4 Spade
24VAC In From Transformer
GND
1/4 Spade
To Cabinet Ground
Y
Screw Strip
Cooling Demand
G
Screw Strip
Blower Demand
R
Screw Strip
24VAC to Thermostat
W
Screw Strip
Heating Demand
C
Screw Strip
24VAC Common
120VAC HOT
1/4 Spade
Line Voltage In
120VAC RTN
1/4 Spade
Line Voltage Neutral
120VAC TX
1/4 Spade
Line Voltage Out To Transformer
CMB
J20/P20 Pin 1
Switched 120VAC to
Combustion Air Blower
CMB RTN
J20/P20 Pin 2
120VAC Common
Combustion Air Blower
ACB HEAT
1/4 Spade
Switched 120VAC to
Blower Heating Tap
ACB LOW
1/4 Spade
120VAC Output to Supply Air
Blower for Continuous Opera-
tion During No Demand
ACB COOL
1/4 Spade
Switched 120VAC to Blower
Cooling Tap
VLV HOT
J20/P20 Pin 13
24VAC to Gas Valve
VLV RTN
J20/P20 Pin 9
24VAC Common From
Gas Valve
PSW IN
J20/P20
Pin 10
24VAC In From Pressure Switch
Switch Open: Prohibits Ignition
Switch Closed: Allows Ignition
HIL IN
J20/P20
Pin 11
24VAC In From Limits
Limit Open: Closes Gas Valve
Limits Closed: Allows Ignition
HIL OUT
J20/P20
Pin 14
24VAC to Limit Train
and Pressure Switch
RO OUT
J20/P20 Pin 7
24VAC Out To Rollout Switches
RO IN
J20/P20 Pin 15 24VAC In From Rollout Switches
SPARK
ELECTRODE
Male Spark
Plug Type
High Voltage Out To
Spark Electrode
FS
J20/P20 Pin 12
Flame Microamp Sensing
FIGURE 10
FAN-OFF TIME ADJUSTMENT SWITCHES
LOCATED ON FURNACE CONTROL (A3)
Fan-Off Timings
Switch
1
2
Timing
Seconds
Off
On
Off
Off
Off
On
On
On
120
90
180
240
Diagnostic LED
The furnace control is equipped with a diagnostic LED
used for troubleshooting the unit and the control. LED
functions are shown in table 7.
TABLE 7
Furnace Control A3 Diagnostic LED
LED State
Meaning
Remedy
Steady On
Control Failure
Replace Control
Slow Flash
Normal Operation
and No Call For Heat
- - - -
Fast Flash
Normal Operation
with Call For Heat
- - - -
Two
Flashes
Control Lockout
Failed to Sense or Sustain
Flame. Check Gas Valve,
Burners, Spark Electrode
and Wire, Flame Sensor.
Replace Control If All OK.
Three
Flashes
Pressure Switch Open
Failed to Prove Combus-
tion Blower Operation or
Blocked Vent. Repair or
Replace as Necessary.
Four
Flashes
Open Limit
Check Primary Limit,
Rollout Switches and Sec-
ondary Limits. Find source
of Overtemperature. If all
OK, Reset or Replace Lim-
its as Necessary.
Five
Flashes
Flame Sensed and Gas
Valve Not Energized.
Check Gas Valve. If OK,
Check Flame Sensor.
B--Blower Motors and Capacitors
All G24M units use direct drive blower motors. All mo-
tors used are 120V permanent split capacitor motors to
ensure maximum efficiency. See table8 for ratings.
TABLE 8
G24M BLOWER RATINGS 120V 1PH
BLOWER MOTOR
HP
G24MQ2
G24MQ3
G24MQ3/4
CAP
1/2
1/3
1/4
5MFD 370V
5MFD 370V
7.5MFD 370V
G24MQ5/6
G24MQ4
G24MQ4/5
1/2
7.5MFD 370V
3/4
40MFD 370V
3/4
40MFD 370V
FIGURE 11
SUPPLY AIR BLOWER
AND SECONDARY LIMITS
Front
Bottom
Right
Left
Top Back
BLOWER
MOTOR
To Remove Blower From Unit: Remove Bolts and
Wiring Jackplugs. Then Slide Out Front of Unit.
MOTOR
CAPACITOR
SECONDARY
LIMITS (S21)