Sequence Of Operation - International comfort products F8MXN Installation Instructions 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 55, 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 26 for thermostat connections.)
The wall thermostat "calls for heat," closing the R−to−W
circuit. The furnace control performs a self−check, veri-
fies the pressure switch contacts PRS are open, and
starts the inducer motor IDM.
a. Inducer Prepurge Period− The inducer enable relay
contacts IDR close and allow 115 VAC to inducer mo-
tor. As the inducer motor IDM comes up to speed, the
pressure switch contacts PRS close to begin a
15−second prepurge period.
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 re-
lay 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 termin-
al. 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
44
f. Heat−Off Delay− When the thermostat is satisfied, the
2. Cooling Mode
The thermostat "calls for cooling."
a. Single−Speed Cooling
b. Two−Speed Cooling
3. Dehumidify Mode
(See Figure 27 − Figure 30 for humidity sensing ther-
mostat 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 dehumidi-
Specifications are subject to change without notice.
EAC 1 AMP is energized and remains energized as
long as the blower motor BLWM is energized.
R−to−W circuit is opened, de−energizing the gas
valve GV, stopping gas flow to the burners, and de−en-
ergizing the humidifier terminal HUM 24 VAC. The in-
ducer motor IDM will remain energized for a 5−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 fact-
ory−set for a 120−second heat−OFF delay.
(See Figure 26 − Figure 33 for thermostat connec-
tions)
The thermostat closes the R−to−G−and−Y circuits.
The R−to−Y circuit starts the outdoor unit, and the fur-
nace control R−to−G−and−Y/Y2 circuits start the fur-
nace blower motor BLWM on COOL speed.
The electronic air cleaner terminal EAC 1 AMP is ener-
gized 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 contin-
ue 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 25)
(See Figure 26 − Figure 33 for thermostat connec-
tions.)
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 fur-
nace control R−to−G−and−Y1 circuit starts the fur-
nace 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 fur-
nace 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 ener-
gized 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 25)
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