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.
CAUTION:
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.
II.
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. 16, 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,” 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 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 time before a
lockout occurs. Lockout automatically resets after 3 hr, or can be
manually reset by turning 115–v off (not at thermostat) for 3 sec
minimum, then on again.
Fig. 14—Furnace Control
A00292
G
R
Y
W
Com
24V
HUM
3-AMP FUSE
HUMIDIFIER TERMINAL
(24-VAC 0.5 AMP MAX)
LED OPERATION &
DIAGNOSTIC LIGHT
HARNESS CONNECTOR
24-V TRANSFORMER SEC-2
SPARE-1
SPARE-2
EAC-1 (BLACK)
EAC-ELECTRONIC AIR CLEANER
TERMINALS (115-VAC 1 AMP MAX)
EAC-2 (WHITE)
115-VAC (L2) NEUTRAL
CONNECTION
24-V THERMOSTAT
TERMINALS
BLOWER SPEED
SELECTION TERMINALS
INDUCER MOTOR
CONNECTOR
115-VAC (L1)
POWER SUPPLY
HOT SURFACE
IGNITOR CONNECTOR
HEAT
COOL
BLOWER OFF DELAY
ADJUSTMENT SWITCH
SEC-1
TEST/TWIN
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