Air Conditioning, Electrical Motor, and Electrical Service Questions

I pulled the cap out. It’s labeled 45 uf and 7.5 uf. It does start both motors: One terminal labeled “FAN” goes to the fan, one labeled “HERM” (?) goes to the compressor, and one common “C” terminal.

The AC had been off for overnight before I started it this morning, and I got the fan spinning the first try. It’s one cap for both motors, so it’s getting replaced at any rate. Hopefully I didn’t get a freon dump.

Thanks everyone. I’ll update when I get a replacement capacitor.

Also, in the spec sheet, it’s 40 amps, so the breakers are wired correctly, just mislabeled.


This. :slight_smile:

I got the fan going pretty quickly when I turned it on this morning. Also, it’s raining pretty hard right now, so I’m just going to leave it until I replace the capacitor.

I can honestly say I’ve never heard of a ‘freon dump’. I’ll add that I don’t tinker much with car or huge industrial rack systems and maybe that’s where they exist, but I’ve never seen or heard of one on a commercial or residential system. Of course I’m self taught and don’t tinker with the freon side of things, but if it was common, I likely would have seen or heard of it.
At least in commercial systems, if the high side gets to high, there’s a high pressure cut off switch that shuts down the system. I can’t see why you’d want to blow out your refrigerant due to a failed fan, it seems like the EPA would be all over that.

Looking around on the internet, it seems the relief valves are common on cars, but I can’t seem to figure out why they have them. My only guess is that it’s cheaper then putting in a pressure sensor and so rare for the freon to blow off that the EPA ok’d it since there’s such a small amount of refrigerant in the car. I’d guess probably less then a quarter of a pound. That may even be under the amount that a person/business is allowed to leak in a year without it being reportable.

ETA, I think part of the reason is that in a lot of states it’s legal to charge your own AC system. The relief valve may help save a lot of people from over charging their system and destroying it.

I ordered this capacitor, which matches the specs of my old one (including the 440 V). It’s supposed to arrive Tuesday.

Auto systems do have high pressure cut outs.

Most commercial AC systems that I have worked on do have a relief valve. Systems from 20 to 3200 tons. The relief is incase all the other safeties have failed. In all my years I have only heard one one lifting and that was a 300,000 ton NH3 plant.



I saw the UPS driver on the way home, so as soon went in the house, I got the package, opened it and installed. Turned on the AC, went outside, and the fan was running, and the air coming out seemed warm. Checking the air inside coming from the vents, it was cool, but not as cold as I recall it had been. But the house was a lot warmer than it usually is. More humid, too, and dehumidifying the air has to take away some cooling capacity. An hour into it, the house has dropped a degree, and the vent air is cooler than at first.

For the “maybe” part, the capacitor was dented in its side when it arrived. I shook it, and could hear liquid sloshing around inside. :eek: The old one didn’t slosh! OK, the old one didn’t work either.

Is this normal for this size and type of capacitor? When I installed it, I honestly didn’t think it was going to work. I’m still afraid it’s going to fail soon.


Does anyone know if the liquid in a large motor capacitor should be sloshing?

The capacitor’s main function is to get the motor and /or compressor started. I don’t know if yours is bad or not. The sloshing may just be the oil that is used as an insulator between the capacitors charge plates.

It’s easy to see if the outside fan is running but can you verify that the compressor is running?

I once had an AC unit that wasn’t cooling and the service tech told me that the compressor was wearing out and required more torque to get it started. On my unit I could hear the cooling fan running but it was obvious (the compressor makes a lower rumble sound) that the compressor wasn’t.

The tech bought me a couple more years of operation by installing a “hard-start” kit which was nothing more than a capacitor that was larger than the original. But the compressor eventually wore out all together and it became time to reach deep into the checkbook and replace the outdoor unit.

If the compressor is running and you still aren’t cooling the house it may low on refrigerant (freon),

The AC is running. The old capacitor was bad. The new capacitor is currently working correctly, starting both the fan and the compressor.

I would expect a capacitor to be full of any liquid, and to not also have a gas in it. I don’t have any experience, to know if this is normal or not. My concern is that, while it is working now, it may fail after a short time. If it’s normal for the liquid in them to slosh around when shaken, I’d like to know that.

I have never seen a small cap that sloshed.

Same here, I think in all my time I’ve only handled a few of them and usually as part of the motor that’s getting replaced, but I don’t recall any sloshing.

If there’s a local Grainger near you, you could have them pull one and see if it sloshes. They might just let you swap it. Otherwise, I might consider just biting the bullet and buying a new one.

Also, looking at the link you provided, there’s no MSDS and it doesn’t list anything about being ‘oil-filled’ which makes me think if it’s not supposed to be filled (with anything). Between that and the dent, I might be weary. If you call Grainger, they’re usually very helpful with this kind of thing. They’ll be able to transfer you to someone that can answer these questions about the specific cap you’re looking at.