Furnace blower not starting in auto mode.

Old 11-17-18, 08:14 AM
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Furnace blower not starting in auto mode.

I noticed the temperature dropping below the thermostat set point. Checking the American Standard Freedom 80 two-stage furnace, I found it cycling without the blower engaging and providing a diagnostic code of 4 blinks indicating an open limit device.

With each cycle, I can hear/see the vent fan start and the gas ignition, which will burn for a while, then shut off and recycle.

I switched the fan at the thermostat from Auto to On and the furnace is now heating the house. While running in the On position, I switched it back to Auto and it continues to run. I lowered the thermostat set point to test the Auto setting. The flames shutdown, then eventy the blower shut off. I then increased the set point, the vent and flames turn on, and now the blower turns on as expected.

Perhaps I reset the limit switch by running the fan for a while. Id still like to know the reason the furnace blower wasnt kicking on earlier.
Old 11-17-18, 04:04 PM
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Welcome to the forums.

The safety limit is self resetting. You need to determine if the furnace blower is controlled by a timed function on the control board or has a separate fan/limit switch for the blower in heat mode. I suspect that it is control board timed as it's a two stage (newer) unit.

You'd need to remove the burner service door and get the model number that is posted on an ID tag on the side wall near the burner for me to comment further.

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