I finished another DIY project — a repair — yesterday but I made several errors with this one. I’ll go into those. I want to also mention that I stayed overly zealous about throwing circuit breakers, ensuring everything was off, and cautiously touching wires. I won’t dwell on it, but I took constant steps to stay safe and unharmed. I was messing with 240 V a lot of times, and I stayed respectful of that.

Our air conditioning went out. Fortunately, the weather here hasn’t been too hot this year; we’ve yet to break 100 degrees F, and temperatures have been dropping into the upper 50s/low 60s at night. We also haven’t been inundated with wildfire smoke, so the air remains relatively clean, fresh, and healthy. It’s a mighty confluence of good fortune. We’re able to open doors and windows at night and in the morning to air the house out, dropping the inside temperatures to about 72 F. We just need to be aware of wildlife like skunks, raccoons, bears, deer, and cougars in the area, and make sure none of them wander in. Then we close almost all back up for the day, including the blinds, and keep the house cool. This works pretty well; it rarely pops over 82 F in the house, and that feels oddly comfortable. We do have a fan that we’ll kick on if we feel the need.

But one day, my wife said, “Turn on the air,” and I did, and it didn’t. The house blower went on but there was nothing from the condenser or fan. I immediately said, “Capacitor.” It’s gone out twice in the seventeen years we’ve owned the house, which was bought new. I ordered a new one, turned off the circuit breakers, pulled the A/C switch, removed the panel, and replaced the capacitor. All good, right?

No. I inspected the capacitor. Didn’t see any swelling or anything unusual. Wires were all connected. Hmmm.

Continuing on my mistake-strewn path, I powered the unit up and manually pressed the connector’s pull in. Power to the unit. Condenser and fan went on.

Well, damn. A bad connecter then? I ordered a new one and duly installed it. No change. Say what? I’d photographed the wires before swapping the part and poured over them now, ensuring I had them all right and secure. They were. Nuts.

Well, then, it must be the thermostat.

I’d replaced it last year. Maybe I’d done something wrong. I checked all of its wiring. Everything was correctly connected and tight. I replaced the batteries so they were new. No change.

I started searching the net for what the heck was wrong. This is something I should have done in the beginning. Pulling out the multimeter, I checked power at the unit — yep, 240 running into it, no surprise, as it fired before. No low voltage going into the connecter.

Whaaat?

The wires all looked good. Connections were solid, but nothing registered. Nothing. No damage visible. No nests, spiders, or insects. No traces of mice. Huh.

Back at the thermostat, I placed my probes against the red (power) and yellow (cooling) wires. 24 volts.

Then it must be on the furnace control board.

Nuts.

We have a side mounted furnace. It’s up in the attic above the garage. It’s a low, hot space. I dislike going up there and working on the furnace. It means pulling the car out, and using two ladders. One must be climbed to remove the access panel, but that ladder isn’t tall enough for me to safely climb and get up into the space. I must use a second, taller ladder, putting it into the access panel’s open space to climb up into the attic.

The furnace’s control board’s green light was lit but blinking. That’s how it usually is. I removed the access panel with the idea of checking all the wires. Yep, five into the thermostat connections, just as shown on the videos. Second was the fuse. Fuse was great. Next, I was going to check the low voltage power out of the stepdown transformer. As I was approaching that, I noticed a wire not connected to anything.

A yellow wire.

Now, you might think that’s obvious. In hindsight, it is. But there’s a large coil of installed but unused wires up there. That gave me uncertainty; maybe it wasn’t meant to be used.

I was thinking about all I learned but I still had just a nascent understanding of everything. Back down I went to videos. I really enjoy the Word of Advice series on Youtube. He’s patient and thorough.

I watched his video on the control board’s fuse because he was talking in general about the control board and all the wires and their purposes. And he said, “There should be five wires going in for the thermostat and two going out to the outside unit.”

Ding.

I had one going out. The blue one. No yellow one connected.

Power was cut and the connection was made. Success was achieved. The condenser and fan fired up and the house cooled.

Everything was reinstalled, closed up, and powered up. Success, but it was sloppy and haphazard. I should have been methodically testing and studying and not leaping to conclusions without testing. Lesson learned, I hope.