Sail switch usually wont allow ignition, as it has to close to allow things to progress, it's unusual for a switch to close then not. I would consider over temp switch. Could still be some insect debris are blocking airflow to the point where over temp switch is tripping.
Zhavins said the furnace isn't igniting, so the over-temp switch shouldn't affect anything...unless =it's= bad. I say to jumper the sail switch and see if that works before throwing parts at it.
Lyle
Feb 16, 2021 6:48:28 GMT -8 zhavins said:
Update: The furnace worked through about half the night and now stopped working. It turns on for about 30 seconds and it doesn't ignite so it shuts off 30 seconds later. I think I am going to order a new sail switch since that is cheap and a easy/quick replacement. If anybody has any other ideas, please let me know.
He said it worked through about half the night.
Here is Mfg sequence of events- note that the control board checks to see of the sail switch is Open, it then starts the blower motor and checks to see of the sail switch is Closed...
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.
