Step 3--Purge Gas Lines
FIRE AND EXPLOSION HAZARD
Failure to %llow this warning could result in a fire, explosion,
personal injury, or death
Never purge a gas line into a combustion chamber. Never test
for gas leaks with an open flame. Use a commercially
available soap solution made specifically for the detection of
leaks to check all connections.
[f not previously done, purge lines after all connections have been
made and check for leaks.
Step 4--Sequence of Operation
FURNA(E MAY NOT OPERATE
Failure to %llow this caution may result in t:urnace operation
stopping and water pipes freezing during cold weather.
Furnace control must be grounded for proper operation, or
control will lock out. Control is grounded through
green/yellow wire routed to gas valve and burner box screw
[sing the schematic diagram in Fig. 32, fbllow the sequence of
operation through the diffkrent modes Read and fbltow the wiring
diagram very- carefully.
NOTE: If a power interalpfion occurs during a call for heat (W),
the control will start a 90-second blower-only ON period two
seconds after power is restored, if the thermostat is still calling for
gas heating. The red LED light will flash code 12 during the
90-second period, after which the LED will be ON continuous, as
long as no faults are detected. Afier the 90-second period, the
flul_ace will respond to the thermostat normally
The blower door must be installed for power to be condtlcted
through the blower door interlock switch ILK to the furnace
control (PU, transl\_rmer TRAN, inducer motor IDM, blower
motor BLWM, hot-surface igniter HSI, and gas valve GV.
1. Heating
(See Fig 30 fbr thermostat connections.)
The wall thermostat "calls for heat", closing the R to W
circuit. The fl/mace contlol perfbm_s a self-check, verifies the
pressure switch contacts PRS are open, and starts the inducer
motor IDM.
a. Inducer Prepurge Period- As the inducer motor IDM
comes up to speed, the pressure switch contacts PRS close,
24 vac power is supplied fbr a field installed humidifier at
the HUM terminal and the control begins a 15-second
prepurge period.
b. Igniter Warm-Up- At tl-_eend of the prepurge period, the
Hot-Surfi_ce Igniter HSI is energized fbr a 17-second
igniter warm-up period.
c. Trial-Nr-Ignition Sequence- When the igniter warm-up
period is completed, the main gas valve relay contacts GVR
close to energize the gas valve GV, the gas valve opens.
The gas valve GV pemaits gas flow to the burners where it
is ignited by the Hot Surfhce Igniter HSL Five seconds after
the GVR closes, a 2-second flame period begins. The HSI
igniter will remain energized until d-_e flame is sensed or
until the 2-second flame proving period begins.
d. Flame-Proving- When the burner flame is proved at the
flame-proving sensor electrode FSE, the fl/mace contlol
CPU begins the blower-ON delay period and continues to
hold the gas valve GV open. If the burner flame is not
38
proved within two seconds, the control CPU will close the
gas valve GV, and the control CPU will repeat the ignition
sequence fbr up to three more Trials-For-Ignition befbre
going to Ignition-Lockout. Lockout will be reset auto-
matically after three hours, by momentarily interrupting
115 vac power to the furnace, or by interrupting 24 vac
power at SEC1 or SE(2 to the [:urnace control CPU (not at
W, G, R, etc.)
If flame is proved when flame should not be present, the
fhmace control CPU will lock out of Gas-Heating mode
and operate the inducer motor IDM until flame is no longer
proved.
e. Blower-On Delay- If the burner flame is proven, the
blower motor is energized on HEAT speed 66 seconds after
the gas valve GV is energized.
Simultaneously, the electronic air cleaner terminal EAC-!
is energized and remains energized as tong as the blower
motor BLWM is energized.
f_ Blower-Off Delay- When the thermostat is satisfied, the
R-to-W circuit is opened, de-energizing the gas valve GV,
stopping gas flow to the burclers, and de-energizing the
humidifier terminal HLM. The inducer motor IDM will
remain energized for a 15-second post=purge period. The
blower motor BLWM and air cleaner terminal EAC-I wilt
remain energized fbr 90, 120, 150, or 180 seconds (depend-
ing on the blower-OFF delay selection). The flu'hate
control CPU is fitctory-set for a 120-second blower-OFF
delay.
Cooliug Mode
(See Fig. 30 fbr them_ostat connections)
The thermostat closes the R-to-G-and-Y circuits. The R-to-Y
circuit starts the outdoor unit, and the R-to-G and Y circuits
start the t\lrnace blower motor BLWM on COOL speed.
The electronic air cleaner terminal EAC-1 is energized with
115 vac when the blower motor BLWM is operating.
When the thermostat is satisfied, the R-to-G-and-Y circuits are
opened. The outdoor unit will stop, and the t\trnace blower
motor BLWM will continue operating on the COOL speed fbr
an additional 90 seconds. Cut jumper J2 to reduce the cooling
off'delay to 5 seconds. (See Fig. 33.)
Continuous Blower Mode
When the R-to-G circuit is closed by the themlostat, the
blower motor BLWM will operate on continuous-blower
speed (same as HEAT speed) Terminal EAC-! is energized as
long as ff*e blower motor BLWM is energized
During % call for heat(' the blower BLWM will stop during
igniter wam_-up (17 seconds), ignition (7 seconds), and
blower-ON delay (65 seconds), allowing the fhmace heat
exchangers to heat up more quickly, then restarts at the end of
the blower-ON delay period at HEAT speed
In heating, the furnace control CPU will continue running the
blower motor BLWM at HEAT speed after the selected
blower-OFF delay period is completed.
When the thermostat "calls fbr cooling", the blower motor
BLWM will operate at (OOL speed. When the d_em_ostat is
satisfied, the blower motor BLWM will operate an additional
90 seconds on COOL speed befbre reverting back to HEAT
speed. Jumper J2 can be can be cut to reduce the cooling
offtdelay to 5 seconds. (See Fig. 33.)
When the R-to-G circuit is opened, the blower motor BLWM
will continue operating for an additional 5 seconds, if no other
flmction requires blower motor BLWM operation.
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