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NOTE: If there is a power interruption and any thermostat call,
the control initiates a 90-sec blower only on period before starting
a cycle.
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. Igniter warm-up—At the end of the prepurge period, the
igniter is energized for a 17-sec igniter warm-up period.
c. Ignition sequence—When the igniter warm-up period is
completed, the gas valve opens, permitting gas flow to the
burners where it is ignited. After 5 sec, the igniter 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 control
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 sequence.
NOTE: Ignition sequence will repeat 3 additional times before a
lockout occurs. Lockout automatically resets after 3 hr, or can be
manually reset by turning 115v off (not at thermostat) for 3 sec
minimum, then on again.
f. Blower on delay—Forty-five sec after burner flame is
proven, the blower motor is energized on heating speed.
Simultaneously, the electronic air cleaner terminals (EAC-1
and EAC-2) are energized. If jumper is on pins 6 and 9,
blower-on delay is 66-sec.
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 90, 135, 180, or 225 sec (depending
on the blower off delay selection). The furnace is factory
set for a 135-sec blower off delay.
h. Post-purge—The inducer motor remains energized 5 sec
after the burners are extinguished. If jumper is on pins 6
and 9, post-purge period is 15-sec.
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 terminal 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 45-sec blower on delay period.
If jumper is on pins 6 and 9, blower-on delay is 66-sec.
The blower reverts to continuous operation after the heating
cycle is completed.
When the thermostat "calls for cooling," the blower operates
on cooling speed. When the thermostat is satisfied, the blower
operates on cooling speed an additional 90 sec before revert-
ing back to continuous operation on heating speed.
4. Heat pump mode
When installed with a heat pump, the furnace control auto-
matically changes the timing sequence to avoid long blower
off-time during defrost cycles. When the W-Y or W-Y-G
thermostat inputs are received at the same time, the control
changes the blower to heating speed or starts the blower if it
was off, and begins a heating cycle. The blower remains on
until the end of the prepurge period, then shuts off until the
end of the hot surface igniter warm-up and trial-for-ignition
periods (a total of 24 sec). The blower then comes back on at
heating speed.
When the W input signal disappears, the control begins the
normal inducer post-purge period and the blower changes to
cooling speed after a 1-sec delay. If the W-Y-G signals
disappear at the same time, the blower remains on for the
selected heating blower off delay period and the inducer goes
through its normal post-purge period. If the W-Y inputs
should disappear, leaving the G signal input, the control goes
into continuous blower and the inducer remains on for the
normal post-purge period.
Anytime the control senses false flame, the control locks out
of the heating mode. This occurs because the control cannot
sense the W input due to the false flame signal, and as a result,
sees only the Y input and goes into cooling mode, blower off
delay. All other control functions remain in standard format.
NOTE: EAC-1 terminal is energized whenever blower operates.
HUM terminal is energized whenever the gas valve is energized.
START-UP PROCEDURES
1. Purge gas lines—After all connections have been made, purge
the lines and check for leaks.
Never purge a gas line into a combustion chamber. Never use
matches, candles, flame, or other sources of ignition for the
purpose of checking leakage. Use a soap-and-water solution
to check for leakage. Failure to follow this warning can cause
fire, explosion, personal injury, or death.
2. Component test—The furnace control allows all components,
except gas valve, to be run for a short period of time.
This feature helps diagnose a system problem in case of a
component failure. To initiate component test procedure, short
(jumper) the TEST 3/16-in. quick connect terminal on board
(adjacent to status light) and the C
thermostat connection block for approximately 2 sec. (See Fig.
10.)
NOTE: Component test feature will not operate if any thermostat
signal is present at control.
Component test sequence is as follows.
a. Momentarily jumper TEST and C
LED goes off.
b. LED will display previous status code 4 times.
c. Inducer motor starts and continues to run for entire com-
ponent test.
d. Hot surface igniter is energized for 15 sec, then de-
energized.
e. Blower motor operates on heating speed for 10 sec, then
stops.
f. Blower motor operates on cooling speed for 10 sec, then
stops.
12
-24V terminal on furnace
OM
-24V terminals until
OM
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