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Initial Power up: After 30 seconds of igniter
warm-up the gas valve (24 VAC) will then
open. The igniter circuit will stay ener-
gized for 3 seconds after the gas valve
opens.
After Initial Power up: The control has a
programmed adaptive ignition feature
which varies the warm-up period as fol-
lows: If ignition is successful the warm-up is
reduced by 3-seconds on each subsequent
call for heat until ignition failure occurs.
Upon ignition failure, the warm-up is in-
creased by 3-seconds on the next try. If
successful, the timing remains fixed at this
level. In general, whenever ignition failure
occurs the warm-up interval is increased by
3-seconds on the next try. And if success-
ful, it remains there. Minimum and maxi-
mum warm-up time limits are set at 6 and
54-seconds, respectively.
7. The furnace control must prove flame via
the flame sensor 5 seconds after the gas
valve opens. If flame is sensed, all burn-
ers are on and the ignitor cools off. If no
flame is sensed, the gas valve closes
immediately and the inducer continues to
run. A second trial for ignition (step 6)
begins if no flame is sensed. On the fifth
try for ignition, the furnace control is locked
out and the red LED will blink 4 times
repetitively. The thermostat must be
opened for at least ten seconds to reset
the furnace control after a lock out. Oth-
erwise, the furnace will attempt another
ignition sequence in 1 hour.
8. The furnace control energizes the cir-
culating air blower on the heating speed
30 seconds after the gas valve circuit is
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 tech-
nician to identify and repair the problem.