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115-VAC (L1)
POWER SUPPLY
IGNITOR CONNECTOR
1. Heating mode
When the wall thermostat "calls for heat," the R-W circuit
closes. The furnace control performs a self-check, verifies
the pressure switch contacts are open, and starts inducer
motor.
a. Prepurge period—As the inducer motor comes up to
speed, the pressure switch contacts close to begin a
15-sec prepurge period.
b. Ignitor warm-up—At the end of the prepurge period, the
ignitor is energized for a 17-sec ignitor warm-up period.
c. Ignition sequence—When the ignitor warm-up period is
completed, the gas valve opens, permitting gas flow to
the burners where it is ignited. After 5 sec, the ignitor is
de-energized and a 2-sec flame-sensing period begins.
d. HUM terminal is energized with the gas valve. See
accessories in the Electrical Connections section.
e. Flame-sensing—When burner flame is sensed, the con-
trol begins the blower on delay period and continues
holding the gas valve open. If burner flame is not sensed,
the control closes the gas valve and repeats ignition
cycle.
NOTE: Ignition sequence will repeat 3 additional times before a
lockout occurs. Lockout automatically resets after 3 hrs, or can be
manually reset by turning 115v off (not at thermostat) for 3 sec
minimum, then on again.
f. Blower on delay—Forty sec after burner flame is proven,
the blower motor is energized on heating speed. Simul-
taneously, the humidifier and electronic air cleaner
terminals (HUM and Com for humidifier, EAC-1 and
EAC-2 for electronic air cleaner) are energized.
TEST/TWIN
SEC-1
3-AMP FUSE
COOL
HEAT
HOT SURFACE
INDUCER MOTOR
CONNECTOR
Fig. 9—Control Board
24-V THERMOSTAT
TERMINALS
HUMIDIFIER TERMINAL
(24-VAC 0.5 AMP MAX)
HUM
LED OPERATION &
DIAGNOSTIC LIGHT
HARNESS CONNECTOR
24-V TRANSFORMER SEC-2
SPARE-1
BLOWER SPEED
SELECTION TERMINALS
SPARE-2
EAC-1
EAC-ELECTRONIC AIR CLEANER
TERMINALS (115-VAC 1.5 AMP MAX)
EAC-2
115-VAC (L2) NEUTRAL
CONNECTION
g. Blower off delay—When the thermostat is satisfied, the
circuit between R-W is broken, de-energizing the gas
valve stopping gas flow to the burners. The blower
motor and EAC remain energized for 135 sec.
h. Post-purge—The inducer motor remains energized 5 sec
after the burners are extinguished.
2. Cooling mode
When the thermostat "calls for cooling," R-G and R-Y
circuits close. The R-Y circuit starts the outdoor condensing
unit and the combined R-Y and R-G circuits start the
furnace blower motor on cooling speed. The EAC-1 termi-
nal is energized with 115v when the blower is operating on
cooling speed.
When the thermostat is satisfied, R-G and R-Y circuits are
broken. The furnace blower and EAC continue operating on
cooling speed for an additional 90 sec.
3. Continuous blower mode
NOTE: EAC-1 terminal is energized with 115v whenever blower
operates.
When the R-G circuit is made, the blower motor operates on
heating speed. During a call for heat, the blower stops,
allowing the furnace heat exchangers to heat up more
quickly, then restarts at the end of the 40-sec blower on
delay period.
The blower reverts to continuous operation after the heating
cycle is completed.
When the thermostat "calls for cooling," the blower oper-
ates on cooling speed. When the thermostat is satisfied, the
blower operates an additional 90 sec before reverting back
to continuous operation on heating speed.
—9—
A95086
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