CONQUEST 80 - Fan Control Board Responses; Integrated Furnace Control (Ifc)

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FAN CONTROL BOARD
RESPONSES
RESPONSE TO LIMIT OPERATION:
If a limit opens during normal
operation, the burners shut off and
the control runs the main blower
motor until the limit resets. After the
limit resets, the main blower motor
runs until timed off by the control
board.
RESPONSE TO CONTINUOUS
BLOWER THERMOSTAT SETTING:
The control operates the indoor
blower continuously on the heating
speed when the thermostat is set to
the heat mode and the fan switch is
set to "On." When the gas valve
opens during a heat call, the fan
continues operating on the heating
speed. It continues on the heating
speed until set to "Auto" on the
thermostat.
If set for continuous fan in the cooling
mode, the fan runs continuously at
the heating speed. When the
thermostat calls for cooling, it runs
the fan on the cooling speed.
RESPONSE IF PRESSURE SWITCH
OPENS: If the pressure switch opens
during operation, or doesn't close on
start up, the gas valve closes. The
inducer blower operates indefinitely
until the switch closes or the heat
call ends.
RESPONSE IF OVER
TEMPERATURE SWITCH OPENS:
An open over temperature switch
breaks 24-volt power to the
thermostat and the control board.
This shuts down the burners and runs
the main blower. After the over
temperature switch is manually reset,
the main blower continues running
until timed off.
INTEGRATEDFURNACE
CONTROL
(IFC)
► Honeywell and United
Technologies (UTEC), and Johnson
Controls (JCI), are the manufacturers
of integrated furnace control (IFC)
boards. This solid-state integrated
furnace control board manages the
operation of the furnace. It
sequences the unit on, ensures that
the furnace operates properly and
stops furnace operation if it detects a
malfunction.
Those controls generally operate the
same. They use the process of flame
rectification to monitor flame
presence and sequence the burners
on and off similarly.
SEQUENCE OF OPERATION
► Current production Honeywell,
JCI, or UTEC Integrated
Controls with electronic
ignition.
1. Each time the thermostat
contacts close the induced
draft blower operates a
prepurge cycle.
2. The air proving negative
pressure switch(es) close .
3.
► 30 seconds after the
pressure switch closes Its
contacts, EITHER the hot
surface igniter heats for 30
seconds to full temperature,
OR the direct spark ignition
electrodes spark. The induced
draft blower continues to run for
the complete heating cycle.
4.
► EITHER after the 30 second
igniter warm up, OR when the
electrodes begin sparking, the
gas valve opens for an 8
second trial for ignition.
5.
The igniter lights the gas burners
and stays energized for the
first 7 seconds after the gas
valve opens.
6. After the igniter de-energizes the
remote flame sensor must
note flame ignition within one
second using the process of
flame rectification. If flame is
not sensed, the system goes
through another ignition
sequence. It does this up to four
times.
7.
The main blower starts
22 seconds after the gas
valve opens.
8.
When the thermostat cycle ends,
the gas valve closes, the burners
go out, the induced draft fan runs
for a five second post-purge,
then the negative pressure
switch opens.
9.
The main blower continues until
timed off by the setting on the
integrated furnace control board.
Sequence if the system doesn't light
or doesn't sense flame:
1.
On a call for heat the control
runs the inducer for 30 seconds
to prepurge.
2.
After the 30 second prepurge,
the hot surface igniter heats for
30 to 34 seconds. The inducer
continues to run.
3.
After the 30 to 34 second igniter
warm up, the gas valve opens for
an 8 second trial for ignition. The
inducer continues and the igniter
stays energized.
4.
If flame is not sensed during the
eighth second after the gas valve
opens, the gas valve closes, the
igniter de-energizes, both the
inducer and main blower
operate for 180 seconds.*
5.
The igniter heats for 30 to 34
seconds. The gas valve then
opens for 8 seconds. If no flame
is sensed after 8 seconds, it
closes the gas valve, the igniter
de-energizes, the inducer runs
for 30 seconds more before
the next ignition trial.
6.
It repeats this process up to
three more times. At the end of
the last try, the inducer stops.
The system is in "soft" lock
out.
7.
To reset the lock out, make
and break power either at the
thermostat or at the unit
disconnect switch. It then goes
through another set of trials for
ignition.
*NOTE: Current integrated
furnace control instructions are
now modified to allow TWO
attempts at ignition before
running blowers for 180 seconds
in "self-healing."
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