Ac kicks on when furnace kicks on


Old 12-19-16, 02:24 PM
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Ac kicks on when furnace kicks on

Hello all. I recently ran into the problem of my outside ac unit kicking on when my furnace kicks on preventing me from getting heat. I noticed that someone moved the fan switch on the thermostat to on so I moved it back to auto but the ac is still kicking on. My gas furnace is relatively new and is working fine. I flipped the breaker for the ac unit and am getting heat now but I would like to fix the problem do I need a new thermostat or.... any suggestions would be great thanks
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Old 12-20-16, 06:42 PM
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The only thing I can think of other than a bad thermostat or control board on the furnace is a short between the W & Y wires somewhere between the thermostat & the furnace. I would start at the thermostat just to make sure the wires aren't touching there. No one has recently replaced the stat or worked on the low voltage wiring have they?
Old 12-22-16, 09:32 PM
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A thermostat configured for HP ( heat pump) would cause this issue.
This is sometimes a switch behind the thermostat.

Replacing the batteries in a thermostat might put someone in proximity to this switch.

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