Last evening as I was winding down from WFH’ing I noticed a rattling noise coming from the direction of my neighbor’s house. I didn’t think much of it, other than assuming that said neighbor had set up some kind of machinery that converts electrical energy into rattling noises, and who am I to judge how said neighbor wishes to spend his electricity budget. As it didn’t anyone in the house, I left it at that.
Of course I didn’t leave it at that, though. Why do you think I’m writing this post in the first place? The rattling noise kept rattling into the night and lightly intruding into my Oppo-reading activity, so I walked out to see if I could find the source of that noise. As I turned the corner I began to notice that the sound was coming not from the property of my neighbor with the three fifth-gen Altimas of different colors, but from my house’s air conditioning condenser unit. And it wasn’t just a noise like that of a bad motor bearing, but a full-on maraca band that I had never heard before. Not Good®.
Hold up. It’s not hot inside the house, why is the outside unit running? Time to check the thermostat. Three full degrees below the programmed threshold. Bugger. Maybe my thermostat is bad? Shut it off. No change. Pull it from the wall. No change. Pull the batteries, put them back in, reinstall the thermostat. No change. Go downstairs and check the heat exchanger. It’s not running. This. Is.
Sparta Bad. I can already feel my sphincter clenching in anticipation of the HVAC repair bill.
Thinking that maybe the noise is caused by the compressor hitting some pressure threshold due to the heat exchanger not heating the gas on the low pressure side, I switched the air handler from Auto to On and checked the vents, confirming cold air coming out. About a minute later, the rattling subsided, although the outside unit was still running. The temperature in the thermostat was still lower than the set point, though. Hhmmm. So I turned off the fan and cut the power to the outside unit at the outside switch and the breaker panel and sat down to investigate (read: hit the Googles). I quickly found an answer, pointing to the contactor welding itself closed and preventing the compressor motor from shutting off when the thermostat has de-energized its coil. Ooooh.
Now that I had a something to try, I left it powered off overnight so I could look further into it today. After taking the wrong brake parts to FexEx to RMA them back to RockAuto, I took a few tools out and went to the outside unit to check it out. Just four sheet-metal screws held the side panel in place, which when removed revealed the prime suspect in plain sight.
After taking a few pictures that had nothing to do with planning to post to Oppo I swear to dog, I pulled the wires, unscrewed it from the frame, and then started to look for a hardware store that may have these in stock. I found a few places, but most close on Saturdays. One was open, and a phone call revealed that they have many types in stock. It’s a 21-mile drive there across twisty mountain roads — yay Miata driving time. They close at 4pm, though, and it’s 2pm when I called the store to inquire. Shit, gotta move.
So I got there with the old contactor in hand and they ask me what type it is. Sure, it’s a 40-amp double-pole. What coil voltage, they ask. Record scratch noises. Apparently I needed to know this ahead of time or test it in place to know what voltage the thermostat sends to energize the coil. Sure, I could do that, but I ate 45 minutes getting there, and there was no way that I’d be able to drive back home, test the voltage, and drive back before they close for the day. Meanwhile the clouds parted and the house has begun to resemble a lime kiln. They also don’t open on Sundays. Helpful fellow there suggested to buy a bunch of them and install the one that matches. They’re cheap enough, so $85 later I had three contactors and a receipt.
Back home, I hooked the multimeter up to the thermostat signal line, turned the thermostat on, and got a 24 VAC reading. Nice. So I started to hook one of the new contactors up according to the pictures that I took, right up until one of the spade connectors for the wires leading to the coil decided that 30 years is a long enough life and decided to break and fall off. Shit, what to do now. I remembered that I had some leftover spade connectors in the garage from when I was doing electrical work in the boat I sold last year, so I walked over there and dug around. Ten minutes later I had two female spade connectors of the right size, which I crimped onto the newly bare wire.
All wired up, I buttoned everything back up and went to do a smoke test. Power to the air handler was on: check. Flipped the breaker to the outside unit, no smoke: check. Outside switch to on, no smoke, compressor doesn’t start immediately: check. Set the thermostat to cool, compressor starts and doesn’t release the magic smoke: check. Put a hand on a vent and confirm cool air: check.
With that done, I sat down for a beer and contemplate how much beer I can buy with the money I saved not having to call an HVAC technician. It's a lot of beer.