Heating, Air Conditioning, Fridge, HVAC/Furnace

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Question
I have a gas furnace thats placed horizontally in the attic and it recently stopped blowing heat. The fan works, but when i switch thermostat to auto, it stops. When i opened the furnace door and saw the switch (that shuts off the furnace when door is open). I held the switch down and i can hear a buzzing sound but nothing happends. A tech came to fix the problem and after replacing the fan relay switch (according to him) it worked for a few hours and after we turned off the heat the next morning and turned it back on at night it didn't work again...Can you help!!!!

Answer
Andrew,
When the thermostat calls for heat the burner lights, The blower starts after a short delay giving the burner a chance to heat the furnace before blowing out air.
It sounds like the blower is working as it should as long as the blower door is closed.
The blower is on a separate 110 volt circuit then the burner which is on a 24 volt circuit.
The way it should work if your furnace has an induced vent pipe blower?
When the furnace calls for heat first the vent exhaust blower starts and runs, next the igniter activates, next the gas valve opens and the infighter lights the burner, next the blower starts.
If the vent blower doesn't, start and run the burner won't light but after a while/delay the blower will start, run, blow cold air.
You need to determine the cycle of the furnace at start.

Heating, Air Conditioning, Fridge, HVAC

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Jim Barnhart

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Fifty + years conditioning the air.

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Answer questions about , residential and commercial. Answer questions about sheet metal fabrication. Fifty years plus experience. No answers for oil equipment, No answers for kitchen appliances, No answers for laundry appliances, I don't specialize in one particular area of the HVAC area, I'm more of a General Practitioner, Limited in refrigeration/

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