Before operating the furnace, check each manual reset switch for
continuity. If necessary, press the button to reset the switch.
The blower compartment door must be in place to complete the
115-v circuit to the furnace.
This furnace is equipped with 2 manual reset limit switches in
the gas control area. The switches will open and shut off
power to the gas valve if a flame rollout or an overheating
condition occurs in the gas control area. DO NOT bypass the
switches. Correct inadequate combustion air supply problem
and reset the switches.
SEQUENCE OF OPERATION
Furnace control must be grounded for proper operation or
control will lockout. Control is grounded through green wire
routed to gas valve and burner bracket screw.
Using the schematic diagram shown in Fig. 13, follow the
sequence of operation through the different modes. Read and
follow the wiring diagram very carefully.
NOTE:
If there is a power interruption and any thermostat call,
the control will initiate a 90-sec blower only on period before
starting another cycle.
1. Heating mode
When the thermostat "calls for heat," R-W circuit closes. The
furnace control performs a self-check, verifies the pressure
switch contacts are open, and starts the 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 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 the 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. Simulta-
neously, the humidifier and electronic air cleaner terminals
(HUM and Com for humidifier, EAC-1 and EAC-2 for
electronic air cleaner) are energized.
g. Blower off delay—When the thermostat is satisfied, the
circuit between R and W is broken, de-energizing the gas
valve and 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
combined R-Y and R-G circuits start the furnace blower motor
on cooling speed. The EAC-1 terminal is energized with 115v
whenever the blower is operating on cooling speed.
When the thermostat is satisfied, R-G and R-Y circuits are
broken. 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
is operating.
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 operates
on cooling speed. When the thermostat is satisfied, the blower
operates an additional 90 sec before reverting back to con-
tinuous 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 demand 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 ignition 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 only energized when 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 line into a combustion chamber. Never use
matches, candles, flame or other sources of ignition to check
for gas leakage. Use a soap-and-water solution to check for
gas leaks. Failure to follow this warning could result in 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.
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