Friday night, it was clear that our upstairs air conditioning wasn't cooling. First I looked at the air handler, and as best I could tell it was fine. I went outside to the other half of the system, and sure enough, it wasn't doing anything. I've seen that before, at a previous house, and I knew that sometimes the compressor and fan would fail to start up due to a dead capacitor. So cool, local hardware store charged $29 for one of those, and I replace it. No good. But what I did noticed this time was hearing the contactor, the thing that uses low voltage to close a high voltage switch, freaked out and clicked a bunch, and wouldn't stay closed. Alas, high voltage scares me, so I decided to defer to a pro. Unfortunately, they couldn't come until Monday, so that meant three nights of no AC upstairs. On the upside, it was cool enough to open all of the windows, but it gets pretty humid overnight so that's not ideal.
The tech rolled up, and it was they guy, along with another last year, that fixed stuff in May. That time, we had no refrigerant, because a wire that was vibrating against one of the pipes from the compressor and rubbed a hole in it. That was a good catch, because they were ready to replace the entire coil. That's why I was OK with waiting for them to have time, because I trust them. This time, after poking around, he found that the control voltage from the inside unit was low. There inside he found that said wire was not exactly connected to the screw terminal, it was just sort of touching it.
Back outside, he could confirm good control voltage, but when the control board's lights went solid as if it should be running, nothing happened. Sure enough, there was no output voltage on the board to the contactor, so with that switch open, no running. On the plus side, you can bypass the controller and have the signal from inside keep the switch closed. However, to reverse the system to heat, or even to institute the "pause" between cycles (to keep wear on the capacitor and compressor down), you need the controller. Sigh. It's probably gonna be a $30 part, plus another service call cost, but servicing this piece of shit is an annual ritual. That last May it was having to fix that hole and then get all new refrigerant, which was expensive. About a year ago I managed to suck all kinds of gross things out of the drip line, which is not Lennox's fault, it was the landscaper. There were two other leak and refrigerant fixes before that, plus the entire condenser coil inside had to be replaced once.
That these Lennox units suck is not a secret. They've been the subject of a class action. Pulte, our shitty builder, provisioned these things all over Central Florida, and many of them have already been replaced. The question now is, do I even bother getting the part, or do I replace some part of the system? That's not an entirely straight forward question. The cost ranges between $4,000 and $15,000 or more. As you may already know, the system has two parts, the outdoor part, which is taking the warm refrigerant outside and blowing air around it to cool it, and the indoor part blows air through it and transfers heat into the refrigerant to send outside. For heat, it just reverses the process (and that works especially well here where it doesn't get that cold).
The rub is that there are three varieties of systems, and it depends on whether or not they can work together. A one-cycle system works at one speed, on or off, while a two-cycle system has a lower power mode that runs slower, for when you need less cooling (or heating) action. Beyond that, there are variable speed systems that can run almost silently when the demand to keep things cool is lower. And just as driving slower is more efficient, so goes HVAC. The variable speed bits are not usually interchangeable though, so you need the matching parts at both ends, and they're more expensive. On the other hand, I could slap another one-cycle part on either end very cheaply.
It's just a math problem, despite my general green hippy sustainable energy ethos. Would an expensive variable speed system save me money in the long run? Obviously it depends on how long we intend to stay here. The general consensus of the Internets says to expect a 15 to 25% savings in HVAC cost. That's like $300 to $500 per year if we knocked that percentage off of our entire electric bill (about $2k a year, because EV's and not enough roof for more solar), so significantly less if it's just the HVAC portion. In other words, if I replace anything, it's probably gonna be just the outdoor unit for upstairs.