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I have Rheem HVAC system that is about 12-4 years old (its an R22 unit). Today it started blowing the fuse on the board when cooling kicks on. The tstat shows a message that says power failure, then 1-2 seconds later, the fuse blows, and the whole thing turns off.

Some additional background:

  • I can run the fan by itself without issue
  • I have an ecobee4 smart thermostat. Today I swapped that out for a 'dumb' tstat to rule that out as the issue. Same problem of blown fuses.
  • About a month ago, I had the opposite problem. The fuse would blow when cooling would stop. I did all the troubleshooting I could Google, and ended up replacing the contactor in hopes that it was somehow shorting out when disconnecting. I used the exact same model number contactor. That seemed to fix it. Until now...
  • "blowing the fuse on the board"... Do you mean your Distribution Board in the house, or is this a fuse on a printed circuit board? If it's the Distribution Board fuse, what size fuse, what size wire and what it the nameplate amp rating of the HVAC unit? – JRaef Jun 3 at 21:25
  • Could be a bad compressor. – Phil Freedenberg Jun 3 at 21:42
  • @JRaef Its the tiny fuse (3A) on the PCB for the air handler. – Zac Jun 3 at 21:51
  • @PhilFreedenberg -- since it's the control fuse, it's probably not the compressor. – ThreePhaseEel Jun 3 at 22:58
  • @Zac -- do you have a multimeter? – ThreePhaseEel Jun 3 at 22:58
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And I'm embarrassed to say that I've figured it out.  I thought I had checked all the wiring, but I missed a small section of exposed copper on the Y wire in the air handler.  Once I taped it up, the problem went away.

Thanks for the suggestions guys!

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