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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 Fig. 16,
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 sec after power is restored, if the thermostat is still
calling for gas heating. The Amber LED light will flash code
12 during the 90−sec period, after which the LED will be ON
continuous, 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 Fig. 2 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 collector
box−LPS and housing pressure switch−HPS are
open, and starts the inducer motor IDM.
a. Inducer Prepurge Period− As the inducer motor
IDM comes up to speed the collector box pressure
switch contacts LPS close to begin a 15 second pre-
purge period. The inducer housing pressure switch
contacts HPS are ignored until one minute after the
gas valve closes.
b. Igniter Warm−Up− At the end of the prepurge
period, the Hot−Surface igniter HSI is energized for
a 17−sec 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 sec after the GVR closes, a 2−sec flame proving
period begins. The HSI igniter will remain energized
until the flame is sensed or until the 2−sec 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 sec, the
control CPU will close the gas valve GV, and the
control CPU will repeat the ignition sequence for up
to three more Trials−For−Ignition before going to
Ignition−Lockout.
automatically after three hours or by momentarily
interrupting 115 vac power to the furnace, or by
interrupting 24 vac power at SEC1 or SEC2 to the
furnace control CPU (not at W, G, R, etc.).
If flame is proved when flame should not be present,
the furnace 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
440 04 7101 09
Lockout
will
be
reset
Specifications subject to change without notice.
EAC−1 is energized and remains energized as long
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
burners, and de−energizing the humidifier terminal
HUM. The inducer motor IDM will remain energized
for a 15−sec post−purge period. The blower motor
BLWM and air cleaner terminal EAC−1 will remain
energized for 90, 120, 150, or 180 sec (depending
on the blower−OFF delay selection). The furnace
control CPU is factory−set for a 120−sec blower−
OFF delay.
2. Cooling Mode
The thermostat "calls for cooling."
(See Fig. 2 for thermostat connections)
The thermostat closes the R−to−G−and−Y circuits. The
R−to−Y
circuit
starts
the
R−to−G−and−Y circuits start the furnace 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 furnace blower
motor BLWM will continue operating on the COOL speed for
an additional 90 sec.
3. Continuous Blower Mode
When the R−to−G circuit is closed by the thermostat,
the blower motor BLWM will operate on HEAT speed.
Terminal EAC−1 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 (7 sec), 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
motor BLWM will operate at COOL speed. When the
thermostat is satisfied, the blower motor BLWM will
operate an additional 90 sec on COOL speed before
reverting back to continuous−blower (HEAT 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
operation.
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−Wand− Y or R−to−W−and−Y−and−G
circuits are energized the furnace control CPU will
continue 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
period, then shut off for 24 sec then come back on at
HEAT speed. When the W input signal disappears,
the furnace control begins a normal inducer post−
purge period and the blower switches to COOL speed
after a 3 sec delay. If the R−to−W−and−Y−and−G
signals disappear at the same time, the blower motor
BLWM will remain 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.
Component Self-Test
Refer to page 14 for instructions.
outdoor
unit,
and
the
23
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