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3 Amp Fuse Keeps Blowing On Control Board

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  • 3 Amp Fuse Keeps Blowing On Control Board

    The 3 amp fuse keeps blowing on the control board when the AC kicks on. It does not happen when the heat cuts on. It appears that the problem is with the outside unit. I have done a lot of troubleshooting and determined it is not the thermostat or the wiring that goes to the thermostat. The system will work when I disconnect the 24v wiring that is connected to the outside unit. The AC cuts on and blows air and does not blow the fuse.
    I checked all visible wiring. The wire was actually cut where it runs out of the attic unit. I fixed this by cutting off the bad portion and then restripping the wires. This did not fix my problem.
    I just purchased this house a couple of months ago. It was a foreclosure and had nobody in it for a couple of years. Therefore the AC hasn't been used in a while.
    The capacitor in the outdoor unit seems to still hold a charge. I know this because, well, it shocked me.

    Any ideas as to what the problem can be from here?

  • #2
    Re: 3 Amp Fuse Keeps Blowing On Control Board

    Without knowing your skill level it is hard to determine if you have the problem isolated or not but if you do it sounds like your problem is in the low voltage pair going out to your condenser (outdoor unit).

    In most systems you will find that pair tied into the common on the control board (White) and the red wire from the condenser will share the Yellow terminal on the board (red wire and yellow wire on same terminal typically.

    IF your colors and wiring are typical you can test my theory by simply disconnecting the red wire (The one from the condenser not the one connected to the R terminal) and see if you are still blowing fuses.

    More often then not an animal or a weedwacker shorts out the low voltage wire to the condenser and will cause the unit to trip in cooling.


    • #3
      Re: 3 Amp Fuse Keeps Blowing On Control Board

      The capacitor in an AC unit should not be shocking you. It is most likely a shock from the power supply not being disconnected.

      At any rate, blowing the fuse when the AC turns on means that there is a short circuit in the low voltage supply to the unit. This cvould be bad wiring, as suggested above, or a failed contactor. In some other, more modern units, it could be a failed circuit board or other wiring to pressure switches.

      ... it was plumbed by Ray Charles and his helper Stevie Wonder