Folly77

Came home Sunday and heat wasn't working. Checked all breakers and disconnects. All good so I opened the unit in the attic and found a 5 amp fuse blown. Replaced fuse and unit ran for about 1.5 hrs then failed. Blown fuse! Replaced again...ran for ~1.5 hrs and failed. Called a friend and he suggested:

1) check 24v control wiring for nicks that may be causing short circuits. Did that at the indoor and outdoor unit and thermostat. Found a few that were questionable so clipped, stripped and re-connected. Replaced fuse...ran for ~1.5 hrs and failed.

2) replace thermostat. Replaced my old analog mercury switch thermostat w/ digital and replaced fuse. It ran about 1 hour and cycled off. Came on and ran about 1 hour and failed.

So what do I check now???

Maverick7687

Check your thermostat wiring. The fuse inside the unit, I am guessing, is fuse for the control board and if there are thermostat wires grounding somewhere it will short this fuse. Had a customer once where mice had gotten in the crawl space and chewed the insulation off the wires but you couldn't see anything visible unless you went under the house so check the whole wire run. I see where you said you checked the 24v wiring but did you go all the way from one end to the other?

Folly77

Thanks Maverick. Turned out to be one of the wires going to the reversing valve at the compressor. It had laid up against the copper tubing and melted so that when the unit went into "defrost mode" (it's been relatively cold in Charleston so it reversed frequently) it would short out and pop the fuse. Explains why it would run for an hour or so before failing. Anyway, seems to be working now. I just wish the weather would warm up!

Maverick7687

NP, Glad you figured it out.. Tape that wire up and zip-tie it somewhere out of the way of that copper line.
I wish it would either snow or warm up here in Knoxville as well, I don't mind the cold if it's snowing, but right now it's just cold for no reason!
Isn't Charleston around where they have the National warning is right now for snow?

Folly77

Charleston, WV maybe but not here. Slight chance of flurries but mostly just cold! Thanks for the advice. I'll make sure it doesn't happen to that wire again.