A/C stopped working and I'm getting low voltage in the line

evgenik25August 23, 2012

My a/c stopped working last night, I tried to troubleshoot the control board in the gas furnace, but discovered that the electrical line that connects to the furnace has 2.2 volts. Voltage is 120 at the fuse and I'm not sure why there is a drop in voltage. Does anyone know what can cause this?


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Are you measuring this the 24 volt supply side? If it is then you may have a bad transformer, or some type of short which is pulling the voltage down to 2.2 volts.

    Bookmark   August 23, 2012 at 11:03AM
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Thank you for your reply. I'm measuring on the primary side. I've disconnected the transformer and measured it directly from the electrical line.

    Bookmark   August 23, 2012 at 11:22AM
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Are you saying the 120v supply is measuring 2.2 volts? If that is true then you either have a bad circuit breaker or an open/poor connection somewhere back to the circuit breaker panel.

    Bookmark   August 23, 2012 at 11:50AM
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Yeah, the 120v supply line is measuring 2.2 volts. Circuit breakers are fine I even replaced the one for the furnace yesterday. I noticed that the supply line doesn't run directly from the circuit breaker to the furnace, any idea on what else it could connect to (maybe the outside unit)?

    Bookmark   August 23, 2012 at 12:00PM
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If the AC is part of a spilt system with an outside condenser, then the supply to the outside should be 240V. It sounds like there is an electrical problem somewhere in the house.

Have you done any recent work in the house where an electrical line may have been cut or altered?

    Bookmark   August 23, 2012 at 5:59PM
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Fuses on the outside disconnect?

    Bookmark   August 24, 2012 at 2:54PM
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