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Step 3--Sequence
of Operation
NOTE:
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 manifold bracket
screw.
Using
the
schematic
diagram
in
Figure48,
follow
the
sequence of operation through the different modes. Read and
follow the wiring diagram very carefully.
NOTE:
If a power interruption
occurs during a call for heat
(W), the control will start a 90-sec blower-only
ON period two
seconds
after power is restored,
if the thermostat
is still
calling for gas heating. The GREEN LED light will flash code
1+2 during the 90-sec
period, after which the LED will be
flashing a heartbeat, as long as no faults are detected. After
the 90-sec
period, the furnace will respond to the thermostat
normally.
The blower door must be installed for power to be conducted
through the blower door interlock switch ILK to the furnace
control CPU, transformer
TRAN, inducer motor IDM, blower
motor BLWM, hot-surface
igniter HSI, and gas valve GV.
1. Heating
(See Figure 26 for thermostat
connections.)
The wall
thermostat "calls for heat," closing the R-to-W
circuit.
The furnace control performs a self-check,
verifies the
pressure switch contacts PRS are open, and starts the
inducer motor IDM.
NOTE:
There are two humidifier terminals available 24VAC
(HUM 24VAC)
and
115VAC (HUM).
Confirm
the correct
terminal to voltage is being used.
a. Inducer Prepurge
Period-
The inducer enable
relay contacts IDR close and allow 115 VAC to in-
ducer motor and HUM terminal (not to be confused
with the 24-v HUM 24 VAC terminal). As the in-
ducer motor IDM comes up to speed, the pressure
switch contacts PRS close, 24 VAC power is sup-
plied for a field installed humidifier at the HUM
24VAC terminal and the control begins a 15-sec
prepurge period.
b. Igniter Warm-Up-
At the end of the prepurge peri-
od, the Hot-Surface
igniter HSI is energized for a
17-second
igniter warm-up
period.
c. Trial-for-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 permits
gas flow to the burners where it is ignited by the
HSI. Five seconds after the GVR closes, a
2-second
flame proving period begins. The HSI
igniter will remain energized until the 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
furnace control CPU begins the blower-ON
delay
period and continues to hold the gas valve GV
open. If the burner flame is not proved within two
seconds, the control CPU will close the gas valve
GV, and the control CPU will repeat the ignition se-
quence for up to three more Trials-For-Ignition
be-
fore going to Ignition-Lockout.
Lockout will be reset
automatically after three hours or by momentarily
interrupting 115 vac power to the furnace, or by
interrupting 24 vac power at 24VAC or COM to the
furnace control CPU (not at W, G, R, etc.) If flame is
proved when flame should not be present, the fur-
nace 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 25
sec after the gas valve GV is energized.
Simultaneously,
the electronic air cleaner terminal
EAC 1 AMP is energized and remains energized as
long as the blower motor BLWM is energized.
f. Heat-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 burners, and
de-energizing
the 24-v humidifier terminal HUM
24VAC. The inducer motor IDM will remain ener-
gized for a 5-second
post-purge
period. Then turn
off the inducer motor and HUM (115-v) humidifier
terminal. The blower motor BLWM and air cleaner
terminal EAC 1 AMP will remain energized for 90,
120, 150, or 180 seconds (depending on the
HEAT-OFF
delay selection). The furnace control
CPU is factory-set
for a 120-second
Heat-Off
Delay.
2. Cooling Mode
(See Figure 26 for thermostat
connections.)
The ther-
mostat 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 furnace blower motor BLWM on COOL
speed. The electronic air cleaner terminal EAC 1 AMP
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 furnace blower motor BLWM will
continue operating on the COOL speed for an addition-
al 90 sec. Cut jumper J2 to reduce the cooling off-
delay to 5 sec. (See Figure 25)
3. Continuous
Blower Mode
When the R-to-G
circuit is closed by the thermostat,
the blower motor BLWM will operate on continuous-
blower speed (same as HEAT speed). Terminal EAC 1
AMP is energized as long as the blower motor BLWM
is energized.
During a call for heat, the blower BLWM will stop during
igniter warm-up
(17 sec),
ignition,
and blower-ON
delay (25 sec), allowing the furnace heat exchangers
to heat up more quickly, then restarts at the end of the
blower-ON
delay period at HEAT speed.
When the thermostat "calls for cooling", the blower mo-
tor BLWM will operate at COOL speed. When the ther-
mostat is satisfied, the blower motor BLWM will operate
an additional 90 sec, on COOL speed before reverting
back to continuous blower speed.
When the R-to-G
circuit is opened, the blower motor
BLWM will continue operating for an additional 5 sec, if
no other function requires blower motor BLWM opera-
tion.
4. Heat Pump
When installed with a heat pump, the furnace control
automatically
changes
the timing sequence to avoid
long blower off times during demand defrost cycles.
When the R-to-W-and-Y
or R-to-W-and-Y-and-G
circuits are energized the furnace control CPU will con-
tinue to turn on the blower
motor BLWM at HEAT
speed, and begin a heating cycle. The blower motor
BLWM will remain on until the end of the prepurge peri-
od, then shut off for 24 sec then come back on at HEAT
speed. When the W input signal disappears,
the fur-
nace control begins a normal inducer post-purge
peri-
od and the blower switches to COOL speed after a 3
sec delay. If the R-to-W-and-Y-and-G
signals disap-
pear at the same time, the blower motor BLWM will re-
main on for the selected blower-OFF
delay period. If
the R-to-W-and-Y
signals disappear,
leaving the G
signal, the blower motor BLWM will continue
running
the blower motor at HEAT speed after the selected
blower-OFF
delay period is completed.
Step 4--Wiring
Diagrams
Refer to Figure 25 and Figure 48 for wiring diagrams.
Step 5--Troubleshooting
Refer to the service label (See Figure 44 or Figure 49).
441 01 1402 02
43
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