Sequence Of Operation - International comfort products F9MXE0401410A Service And Technical Support Manual

SERVICE AND TECHNICAL SUPPORT MANUAL

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 Figure 15, 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−second 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−second period, after which the LED will be
flashing a heartbeat, as long as no faults are detected. After the
90−second 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 17 − Figure 23 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 prepurge
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−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, and 24 vac power is supplied for a
field−installed humidifier at the HUM 24VAC terminal.
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 sequence for up to three more
Trials−For−Ignition before 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
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 seconds
after the gas valve GV is energized.
Simultaneously, the electronic air cleaner terminal EAC
26
2. Cooling Mode
The thermostat "calls for cooling."
a. Single−Speed Cooling
b. Two−Speed Cooling
3. Dehumidify Mode
(See Figure 17 − Figure 23 for humidity sensing
thermostat connections.)
The dehumidification output, H on the humidity sensing
thermostat should be connected to the furnace control
thermostat terminal DHUM. When there is a dehumidify
demand, the H input is activated, which means 24 vac
signal is removed from the DHUM input terminal. In other
words, the DHUM input logic is reversed. The DHUM
input is turned ON when no dehumidify demand exists.
Activation/Deactivation
Once 24 vac is detected by the furnace control on the
DHUM input, the furnace control operates in dehumidify
mode. If the DHUM input is low for more than 48 hours,
the furnace control reverts back to non−humidity sensing
thermostat mode.
The cooling operation described in item 2. above also
Specifications subject to change without notice.
Gas Furnace: (F/G)9MXE
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 humidifier terminal HUM 24 VAC. The inducer motor
IDM will remain energized for a 15−second post−purge
period. 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.
(See Figure 17 − Figure 23 for thermostat connections)
The thermostat closes the R−to−G−and−Y circuits. The
R−to−Y circuit starts the outdoor unit, and the furnace
control R−to−G−and−Y/Y2 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,
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 seconds. Jumper Y/Y2 to DHUM to reduce the
cooling off−delay to 5 seconds. (See Figure 4)
(See Figure 17 − Figure 23 for thermostat connections.)
The thermostat closes the R−to−G−and−Y1 circuits for
low−cooling or closes the R−to−G−and−Y1−and−Y2
circuits for high−cooling. The R−to−Y1 circuit starts the
outdoor unit on low−cooling speed, and the furnace
control R−to−G−and−Y1 circuit starts the furnace
blower motor BLWM on low−cool speed (same speed
as FAN). The R−to−Y1−and−Y2 circuits start the
outdoor unit on high−cooling speed, and the furnace
control R−to−G−to−Y1 and Y/Y2 circuits start the
furnace blower motor BLWM on COOL speed.
The electronic air cleaner terminal EAC 1 AMP is
energized with 115 vac whenever the blower motor
BLWM is operating.
When the thermostat is satisfied, the R−to−G−and−Y1
or R−to−G−and−Y1 and Y2 circuits are opened. The
outdoor unit stops, and the furnace blower BLWM and
electronic air cleaner terminal EAC 1 AMP will remain
energized for an additional 90 seconds. Jumper Y1 to
DHUM to reduce the cooling off−delay to 5 seconds.
(See Figure 4)
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