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TiME linE
DESCripTiOn
Start Time
Thermostat Calls for Heat
The wall thermostat controls the operation of the furnace by reacting to room temperature. This
allows current to flow through the ON/OFF switch to the module board.
The module board constantly checks for a minimum 9.5 volts. if there is not 9.5 volts, the
module board will go into a stand by mode until adequate power is supplied. it will then resume
normal operation.
upon a call from the thermostat, the module board thermostat circuit will go active. The sail
switch circuit is verified as being open. The blower output is energized. Blower motor starts.
15 Seconds Purge Cycle
The module board will then verify that the sail switch circuit is closed and motor is up to speed.
if this circuit remains open for 30 seconds after the blower motor starts, the module board will
go into lockout mode and shut down the blower motor.
The module board checks that the gas valve relay contacts (which are located on the module
board) are open before the ignition sequence starts.
The board has a pre-purge timing circuit of approximately 15 seconds. This allows the
combustion chamber to purge.
7 Seconds Ignition Cycle and
Flame Sense
The module board will energize the gas valve and enable the high voltage spark output to the
electrode for seven (7) seconds of ignition time.
The module board will then check for flame sense to verify successful lighting of the main
burner flame. Sparking of the igniter will then be terminated and the gas valve and blower
outputs will remain energized.
if ignition is successful the module board will monitor the flame sense, sail switch and limit
switch circuits, and the thermostat inputs during the heating period.
The flame is sensed through the spark wire and electrode. Therefore, it is essential that the
electrode is properly positioned in the burner flame.
2nd and 3rd Ignition Cycles if
Required
3 Try Ignition Board
if the flame is
not
sensed after seven (7) seconds, a second 15 second purge cycle will begin
followed by a second Trial-For-ignition sequence. After three (3) Trial-For-ignition attempts with
no ignition of the main burner, the module board will de-energize the gas valve immediately and
blower will run for 3 minutes and then shutdown in lockout mode.
Heating Cycle
if during the heating cycle, the limit switch circuit opens and remains open for 5 minutes, the
module board will go into lock out and shut down the blower motor. if this occurs, the thermostat
will need to be reset for the furnace to operate.
90 Second Shut Down
When the thermostat has reached its set point and the demand for heat ends, the gas valve will
be de-energized and the flame will go out. The post purge period of 90 seconds begins. When
it times out, the blower motor output is removed, and the blower stops.
SEQuEnCE OF OpEraTiOn
FOr Fan COnTrOl MODulE bOarD
parT nuMbEr 520820
