The furnace must have a 115-v power supply properly connected
and grounded. Proper polarity must be maintained for correct
operation. Thermostat wire connections at R, W, C, and Y must be
made at the 24-v terminal block on the control board. The gas
service pressure must not exceed 0.5 psig (14-in. wc), but must be
no less than 0.16 psig (4.5-in. wc).
CAUTION:
This furnace is equipped with a manual
reset limit switch or fuse link in the gas control area. The
switch or fuse link opens and shuts off power to the gas
valve if a flame rollout or overheating condition occurs in
the gas control area. DO NOT bypass the switch. Correct
inadequate combustion air supply problem and reset the
switch or replace the fuse link.
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.
B.
Sequence of Operation
CAUTION:
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. 11, 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 initiates a 90-sec blower only on period before starting
another cycle.
1. Heating mode
When wall thermostat "calls for heat," R-W circuit closes.
The furnace control performs a self-check, verifies pressure
switch contacts are open, and starts inducer motor.
a. Prepurge period—As inducer motor comes up to speed,
pressure switch contacts close to begin a 15-sec prepurge
period.
b. Ignitor warm-up—At the end of prepurge period, ignitor
is energized for a 17-sec ignitor warm-up period.
c. Ignition sequence—When ignitor warm-up period is
completed, gas valve opens, permitting gas flow to the
burners where it is ignited. After 5 sec, ignitor is
de-energized and a 2-sec flame-sensing period begins.
d. HUM terminal is energized with gas valve. See acces-
sories in the Electrical Connections section.
e. Flame-sensing—When burner flame is sensed, the con-
trol begins blower on delay period and continues holding
gas valve open. If burner flame is not sensed, the control
closes gas valve and repeats ignition cycle.
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 sec after burner flame is proven,
blower motor is energized on heating speed. Simulta-
neously, humidifier and electronic air cleaner terminals
(HUM and C
OM
for humidifier, EAC-1 and EAC-2 for
electronic air cleaner) are energized.
g. Blower off delay—When thermostat is satisfied, circuit
between R-W is broken, de-energizing gas valve stop-
ping gas flow to burners. The blower motor and EAC
remain energized for 135 sec.
h. Post-purge—Inducer motor remains energized 5 sec
after 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.
4. Heat pump mode
When installed with a heat pump, the furnace control
automatically 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 re-
mains 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
C.
Start-up Procedures
1. Purge gas lines—After all connections have been made,
purge the lines and check for leaks.
—10—
