Help me control my furnace's blower
February 23, 2011 6:28 PM   Subscribe

How can I reconfigure my Goodman GmH950703Bx furnace so that it doesn't blow all the time?

I have some vents in my slightly-poorly-insulated house that run alongside outer walls, which causes air in them to become cooler than it otherwise would be. That, combined with my new furnace's apparent default setting to always have the blower on, has cool air coming out of the second-story vents when the thermostat detects that the main floor is adequately warm.

My old furnace only ran the blower when the heater was on; at other times it was totally idle. That's the state of affairs I'd prefer to have. The thing is, the wiring for the thermostat has only two wires, which apparently only gives us control of the main on/off control (or something like that -- I'm no expert!).

How should I proceed in resolving this?
posted by ChrisR to Home & Garden (3 answers total)
Your installer has installed your furnace incorrectly.

The old furnace had a single thermometer, probably the classic mercury-switch-on-a-bimetal-coil model, which tripped the furnace to heat up and blow air all at once. All modern furnaces will do what you want, as this diagram suggests.

You'll need to go find yourself a modern thermostat ($30-$50, most places, though you can go cheaper or more expensive) and possibly pull a wire yourself if the installer won't own up to their mistake.

It's not a hard install - get a wiring diagram, though, and pop the breaker before carefully following the instructions - but fishing the wire through can be tough.
posted by mhoye at 6:46 PM on February 23, 2011

Best answer: Two easy to check conditions: 1. ensure the FAN switch on the thermostat is set to AUTO not ON. 2. the plenum heat switch (electrical box mounted to duct work above the unit) is in the AUTO position. Mine is a white knob that is pushed in.
posted by Muted Flugelhorn at 6:57 PM on February 23, 2011

Response by poster: Although mhoye's response is probably the technically-correct one (thanks!) our installation contract did not include extra wiring for the thermostat, so it's probably a non-starter.

It does, however, look like they left the fan in the on mode, which is now changed.

posted by ChrisR at 7:30 PM on February 23, 2011

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