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Matthew, HVAC Technician
Category: HVAC
Satisfied Customers: 2014
Experience:  14 years experience in the HVAC field of service, installation, Manual J & D calculations
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My furnace keeps running constantly. Please help!

Resolved Question:

My furnace is constantly running. I changed the thermostat, but no change. The setting is on heat, and auto fan, but the fan is always on. It heats, and rest of the time circulates the air. It did not do this till 2 weeks ago, we brought a salesman to give us estimate on a new furnace. The only thing I can do is to unplug the furnace to turn off the fan. Please help.

Submitted: 6 years ago.
Category: HVAC
Expert:  Matthew replied 6 years ago.

When you have a moment go to the furnace control board where the thermostat wires hook up and take the wire that hooks to the G terminal off and see what happens. If the blower cuts off go to the thermostat with the wire still unhooked and test the system in heat and cool and see if it works the way it should.

Customer: replied 6 years ago.

Hi, thanks for the responce. The wires are connected to W, and R at the far right. What should I do now?

Expert:  Matthew replied 6 years ago.
You have heat only system then. Is this a gas or electric system? If you could find a model number that would be very helpful.
Customer: replied 6 years ago.

Yes it is heat only unit, and I disconnected W, from thermostat and nothing changed. This is a gas unit and model number from inside of the unit is 396GAW000075.

Expert:  Matthew replied 6 years ago.

That is a serial number I believe not a model number. The model number should start with letters. When the thermostat calls for heat, will the burners come on? And then when the temp is satisfied the burners go off and the fan just runs or do the burners never come on, is it just the fan?

Customer: replied 6 years ago.

The number that I gave you is the model number, there is a product number that is the same as the one I gave you plus ACAA. The serial number is very different.

The heat works fine, but after the shuts off, the fan does not stop, and I feel it is circulating the air.

Expert:  Matthew replied 6 years ago.

Your heat relay which is located on the printed circuit board is malfunctioning, if the heat works when it should, but the blower never cuts off. If the heat never worked and the blower just runs constantly then it would be the fusible link main limit. The only way to repair this is to replace the circuit board.

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