Murphy's Law - HVAC failure

So, we had a little dinner party Saturday night. 10 people about to squeeze around the dining room table. Then my wife taps me on the shoulder and says - isn’t it kind of warm in here?

I check the thermostat, and “cooling” is on, but it’s currently 78 degrees inside. Set point is 76. Uh-oh. I checked one of the registers, and it’s blowing ambient air. Not cooling. The thermostat is on, and the air handler is moving air, so I know it’s not a clogged condensate drain - that kills power to the whole system.

Next, I stepped into the garage where the air handler resides. I can tell immediately by sound that there’s no refrigerant moving. Open the garage door and confirm the compressor is not running. Crap.

I grabbed my power drill and multimeter, and opened up the access panel on the side of the outdoor unit. VERY CAREFULLY measure… 24V on the contactor coil, and 240V on both sides. So power delivery looks good. I’m down to either a bad pressure switch, or a bad start capacitor.

Because this ISN’T my first rodeo, I happen to have a spare HVAC capacitor sitting unopened in my tool chest. So I pulled the service fuse, two screws to remove the old capacitor, hop the wires over to a new one, and put it in place. I plug in the service fuse, and VOILA, the compressor and fan spring to life!

Total time to diagnose and fix: 10 minutes. Had the house cooling before anyone even noticed. Note to self: time to order a new backup capacitor.


Nice work! How’s this for one? My new minisplits wouldn’t come back on a few weeks ago. HVAC guys come out. “Fuses blown”, they say. Hmm I wonder, must have been a power glitch in one of the storms. They go get and replace the fuses. Units come back on. Good, right?

For 5 minutes. Then they just died again. Looks of consternation. The guys go back outside, start diagnosing outside wires, find one from a unit non-responsive, start pulling the vinyl covers off - and out jumps a field mouse from a very large nest he’s made by sneaking in an unclosed end of said covers and chewing up pipe insulation and wires.

New wire homerun to the upstairs unit, insulation replacement, 2 more fuses, a lot of steel wool stuffing and 2 more hours of labor, $725.

Hope I get some of this now $13K system cost back when I sell this place.


Is that what the contractors used to fill the ends of the outside ductwork that houses the wires and copper tubing? If so, I just might go to Home Depot today and buy a bunch and do that myself!! Please let us know!



FYI - Stainless steel pot scrubbers are an option, a better one, won’t rust away, or burn so easy as fine steel wool can do… Sometimes a spark from welding or grinding would catch steel wool on fire in the shop…


Wow… thankfully I’ve never had to deal with mice. It’s probably too hot here for nests in enclosed spaces. The only thing I found was the remains of a small crispy lizard across the leads of the capacitor. That’s a fairly common occurrence based on what I’ve seen opening up AC units over the years.


When I was a kid we would buy steel wool at the hardware store. Then, when it got dark, we would tie a piece to the end of a few feet of zipcord, light it, then swinging it around as fast as possible in a vertical arc. A nice shower of sparks was our reward… cheap fireworks that we couldn’t be arrested for having.



Yes - actually it was stainless steel “wool” or scrubber-similar as wecoguy suggested. It was only really needed on the end where the wiring/hoses from the outside compressor met the house. There’s a long horizontal run, so they stuffed every joint of the outside ductwork with it even though the rest of the run is 5 feet off the ground.

I’ve also spread mothball bags around the base of the compressor to make that an unpleasant place to nest. Depending on temperatures, electricity rates and oil prices the compressor will be running between 3 and 9 months a year from sporadically to continuously.


Thank you!!!