My air conditioner always seemed to run fine except when I tried to run it off my generator. My generator is 3500W so I knew it was more than capable of powering the air conditioner, however, after about 45 minutes of running the generator would bog down and eventually the overload protection would shut it down. I never had any problems with this generator, and had even tried running a friend’s air conditioner off of it, which worked just fine, so I knew it was an issue with my air conditioner. I don’t use the A/C very often when I’m boondocking, however, knowing that I have the ability to run it off my generator if it gets extremely hot out is reassuring, so I wanted to get to the bottom of this issue.

I talked to a few people and did some reasearch on the issue and it seemed that the problem was likely caused by a bad run capacitor. I went in and replaced the run capacitor and that solved my problem, so I wanted to share the steps I went through to replace it.

Run Capacitor vs. Start Capacitor

First it’s worth noting that there are two capacitors in most air conditioner units: a start capacitor and a run capacitor. A very simplified explanation is that the start capacitor helps the motor in the unit to initially start up, while the run capacitor provides a boost in the current while it’s running. If your A/C won’t even initially fire up, it could be an issue with the start capacitor. However, since mine started up just fine and only had problems after it had been running for a period of time, the culprit was more likely the run capacitor. I couldn’t be certain that this was my problem, but I figured that since a replacement capacitor was only about $30 replacing it was worth a shot.

Locating The Capacitors

First and foremost, I completely unplugged my rig from shore power. Once I was disconnected, I climbed on the roof of my rig, removed the cover to the air conditioner, and unscrewed the side panel so that I could access the inside of the unit. On the inside of the panel was a wiring diagram which showed the locations of the capacitors (I outlined the run capacitor in red in the image below).

wiring diagram

From this diagram I could see that the run capacitor had three wires attached to it: red, white, and yellow. So I just needed to find a capacitor with those wires attached to it.

I could see that one of the capacitors was almost totally covered by a wasp nest.

capacitors covered in wasp nest

I very carefully removed the wasp nest, trying not to touch any of the wire terminals. Even though the rig was unplugged, it is possible for capacitors to still hold a charge, so you want to be very careful when handling them.

After cleaning it off I could see this was the one I was looking for. I think it’s possible that this wasp nest could have been the cause of the issue too.

cleaned capacitor

Replacing the Run Capacitor

As I mentioned previously, it’s possible that the capacitor still had a charge, so before doing anything else I got out my multimeter and checked the terminals to see if there was a charge. The multimeter showed 0.0v so I felt it was safe to handle the capacitor. If your capacitor does still have a charge you’ll want to discharge it by shorting it with an insulated screwdriver (you can find plenty of youtube videos demonstrating how to safely do this).

At this point I pulled it out of the brace it was stored in and then was able to find a part number printed on the side. I then took that part number and looked for a replacement online and was able to find one for $30 on Amazon. In the meantime, I left the wires all hooked to the capacitor so that I wouldn’t forget how they were hooked up when the new one came in.

capacitor with part number

When I got the new capacitor I also treated it like it had a charge until I was able to verify with my multimeter that it didn’t. You should always double check any time your handling a capacitor, even a new one. Once I was certain that it was safe, I simply unplugged the wires from the old one and plugged them into the new one, then screwed everything back together. To test it I let my air conditioner run off the generator for about 2 hours and it ran fine the entire time so the problem seemed to be solved.

This turned out to be an extremely easy fix, and I’m sure it saved me a ton of time and money by not having to take it to a dealer. It goes to show that trying to fix things yourself first can really pay off.