HVAC is blowing the fuse on the board when cooling kicks on

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Old 06-03-20, 01:26 PM
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HVAC is blowing the fuse on the board when cooling kicks on

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...
 

Last edited by mattressfish; 06-03-20 at 01:55 PM.
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Old 06-03-20, 05:46 PM
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Since you have a Rheem unit..... they use voltage on the reversing valve only during heating so that won't cause a short issue during cooling.

That leave your Y wire to the contactor inside the condenser. It could be worn/chewed from the house to the condenser. That's a common problems with animals chewing as well the victim of a weed wacker. The Y wire also connects to pressure switches inside the unit and that wiring can short to ground too.
 
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Old 06-03-20, 06:45 PM
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The wires are well protected, so I don't think it could have been a weed wacker, and we really don't have any animal problems in the house that I know of. That said, how can I test this theory?
 
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Old 06-03-20, 06:54 PM
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You can device and conquer. Open the yellow wire/ Y connection at the air handler. See if short is still present. If yes..... go out to the air handler and open the yellow wire/ Y connection where the thermostat cables connect.
 
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Old 06-04-20, 06:26 AM
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So some additional data. I just set the thermostat to call for heat. It did the same thing. Everything turned on and then the fuse blew. Wouldn't it be odd if both wires somehow started shorting on the same day? Could it be something else?
 
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Old 06-04-20, 07:44 AM
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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. Once I taped it up, the problem went away.

DOH!
 
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Old 06-04-20, 12:57 PM
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No problem. Glad you found it. Name:  thumb.jpg
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