Lennox 80MGF Series Manual page 11

Fan OFF" timings (time that the blower operates after a
heating or cooling demand has been satisfied) are de-
termined by the arrangement of switches on the furnace
control board. See figure 5. To adjust fan off " timings,
gently reposition the switches to a new timing position.
Figure 6 shows the various fan off" timings and how
switches should be positioned. 80MGF−1, −2, −3, −4 and −6
units are shipped with a factory fan off" setting of 180 sec-
onds. 80MGF−5 and −7 units are shipped with factory "off"
setting of 60 seconds. Fan off" time will affect comfort and
efficiency and is adjustable to satisfy individual applica-
tions. The fan off" timing is initiated after a heating or cool-
ing demand but not after a blower demand (that is, when
indoor thermostat switch is changed from ON to AUTO
and heating/cooling demand is not present, the blower
stops immediately).
TABLE 2
FURNACE CONTROL A3 TERMINAL DESIGNATIONS
Terminal Type
Y Screw Strip
G Screw Strip
R Screw Strip
W Screw Strip
Early Units
1/4" Spade
C C
Later Units
Screw Strip
120VAC HOT 1/4" Spade
AUX 1/4" Spade
CMB BLWR 1/4" Spade
ACB HEAT 1/4" Spade
ACB COOL 1/4" Spade
VALVE 1/4" Spade
24VAC HOT 1/4" Spade
GROUND 1/4" Spade
FLAME SENSE 1/4" Spade
PSW 1/4" Spade
HI LIMIT IN 1/4" Spade
HI LIMIT OUT 1/4" Spade
ROLLOUT IN 1/4" Spade
Function
Cooling Demand
Blower Demand
24VAC to Thermostat
Heating Demand
24VAC Common 24VAC Common
Line Voltage In
Line Voltage Out (Switched)
Switched 120VAC to
Combustion Air Blower
Switched 120VAC to
Blower Heating Tap
Switched 120VAC to Blower
Cooling Tap
24VAC to Gas Valve
24VAC In From Transformer
To Cabinet Ground
Flame Microamp Sensing
24VAC In From Pressure Switch
Switch Open: Prohibits Ignition
Switch Closed: Allows Ignition
24VAC In From Limits
Limit Open: Closes Gas Valve
Limits Closed: Allows Ignition
24VAC to Limit Train
and Pressure Switch
24VAC In From Rollout Switches
FAN-OFF TIME ADJUSTMENT SWITCHES
LOCATED ON FURNACE CONTROL (A3)
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 3.
Furnace Control A3 Diagnostic LED
LED State
Steady On Control Failure
Normal Operation and
Slow Flash
No Call For Heat
Normal Operation with
Fast Flash
Call For Heat
Two
Control Lockout
Flashes
Three
Pressure Switch Open
Flashes
Four
Flashes
Five Flame Sensed and Gas
Flashes Valve Not Energized.
Page 11
Fan-Off Timings
Switch
1
Off
Off
On
On
FIGURE 6
TABLE 3
Meaning Remedy
Replace Control
Failed to Sense or Sustain
Flame. Check Gas Valve,
Burners, Spark Electrode
and Wire, Flame Sensor.
Replace Control If All OK.
Failed to Prove Combus-
tion Blower Operation or
Blocked Vent. Repair or
Replace as Necessary.
Check Primary Limit, Rollout
Switches and Secondary
Limits. Find source of Over-
Open Limit
temperature. If all OK, Reset
or Replace Limits as Neces-
Check Gas Valve. If OK,
Check Flame Sensor.
Timing
Seconds
2
Off 90
On 120
Off 180
On 240
- - - -
- - - -
sary.