callfor heatuntilignitionfailureoccurs.
Uponignitionfailure,the warm-upis in-
creasedby 3-secondson the nexttry. If
successful,the timingremainsfixed at
this level. In general,wheneverignition
failure occursthe warm-upinterval is
increasedby 3-secondson the nexttry.
Andif successful,it remainsthere.Mini-
mumandmaximumwarm-uptimelimits
are set at 6 and 54-seconds,respec-
tively.
7. Thefurnacecontrolmustproveflamevia
theflamesensor5 secondsafterthegas
valveopens.If flameis sensed,all burn-
ersareonandtheignitorcoolsoff.If no
flame is sensed,the gas valve closes
immediatelyandtheinducercontinuesto
run. A secondtrial for ignition(step 6)
beginsif noflameis sensed.On thefifth
tryforignition,thefurnacecontrolislocked
out andthe red LEDwill blink4 times
repetitively. The thermostat must be
openedfor at leastten secondsto reset
thefurnacecontrolaftera lockout.Oth-
erwise,thefurnacewill attemptanother
ignitionsequencein 1 hour.
8. The furnace controlenergizesthe cir-
culatingair blowerontheheatingspeed
30secondsafterthe gasvalvecircuitis
energized.
9. When the thermostat has been satisfied,
gas valve is de-energized.
10. The inducer is de-energized after a 30-
second postpurge.
11. The furnace control keeps the circulating
air blower energized for 120 seconds
(factory set) or 60, 90, or 180 seconds
(field adjustable). (See Figure 27.)
12. Abnormal conditions: If a limit opens during
operation, the inducer and circulating air
blower continue to operate. The gas valve
is de-energized immediately. The blowers
continue to operate until the limit closes.
When the limit closes the inducer blower is
de-energized immediately. The circulating
air blower continues to operate for the speci-
fied delay (factory set at 120 seconds).
Cooling Mode:
1. On a call for cooling the thermostat closes,
applying 24 VAC to the G and Y terminals
on the furnace control. This closes the
compressor contactor.
2. The furnace control energizes the circu-
lating blower (115 VAC) on the cooling
speed.
3. When the thermostat is satisfied, the G
and Y terminals on the control board are
de-energized opening the compressor
contactor.
4. The circulating air blower is de-energized
after a 90-second delay.
Fan Mode:
1. On a call for fan operation, the thermostat
applies 24 VAC to the G terminal on the
furnace control board.
2. The circulating air blower is energized
immediately on the heating speed.
3. If the furnace is operated in the continu-
ous ON position at the thermostat and is
then switched to AUTO, the circulating
blower will operate for a specified delay
(factory set at 120 seconds).
Furnace Fails to Operate
If the furnace does not operate check the
following:
1. Is the thermostat operating properly?
2. Is the front door in place?
3. Is the furnace disconnect closed?
4. Has the circuit breaker tripped or the
control board fuse burned open?
5. Is the gas turned on?
6. Are any manual reset switches open?
7. Is the filter dirty or plugged?
8. Is the flame sensor coated? (Remove
and clean with emery cloth.)
9. Is the deck switch open?
If the furnace locks out after 5 attempts for
ignition, it will try again every hour if a call for
heat remains. If the inducer and circulating air
blowers are operating, and items 1 through 8
have been checked, press the red reset but-
ton on the vent safety switch. (See Figure 29.)
If the furnace operates after depressing the
reset button, contact a qualified service tech-
nician to identify and repair the problem.
If furnace still fails to operate, depress the red
reset buttons on the flame roll-out switch. If the
furnace operates after depressing the reset
button, contact a qualified service technician
to identify and repair the problem.
31
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