Air Conditioner -Generator bogs down/stalls

Rossi6998 · 08-18-2021, 03:50 AM

Hello all,

Just wanted to share a repair I did to assist others in the future.

If you don't feel like reading the entire post, the point of my post is to suggest if your are having problems with the air conditioner's compressor starting, check the capacitor.

During my monthly maintenance run, I always exercise my Onan Microquiet 4000 generator. As part of the generator process, I run the air conditioner to place a load on the generator.

After starting the generator, I turned on the air conditioner. The fan started without issue, but when the compressor tried to start, the generator bogged down and started to stall. I turned off the air conditioner and waited a few minutes before turning the air conditioner back on. Again, the fan started, but when the compressor tried to start, the generator actually stalled. I plugged the motorhome into shore power and the air conditioner seemed to operate without issue.

Thinking I was having an issue with the generator, I took the motorhome to a Cummins facility to have the generator inspected. I was actually able to get an appointment within two days which obviously pleased me since it is almost impossible to get an appointment with an RV repair facility because a lot of facilities in my area are booked at least two months out.

Cummins inspected the generator, placed a load on it, did some minor adjustments and determined the generator was functioning properly and indicated the problem was my air conditioner. The Cummins paperwork, which was very detailed, indicated when the air conditioner's compressor kicked on the first time, it wanted to draw 35 amps. The generator handled it. They turned everything off, waited a few minutes and turned everything back on. This time the generator stalled because the air conditioner's compressor wanted to draw 50 amps. $140 later, I picked up my motorhome because Cummins does not work on RV air conditioners.

Dreading the thought of having to make an appointment with an RV repair facility, I decided to check the capacitor on the air conditioner. Fortunately, my voltmeter has a setting to check capacitors. After a YouTube search and viewing a couple videos on how to check an air conditioner capacitor, I pulled my capacitor and determined the "FAN" side of the capacitor was fine, but the "HERM" side was giving me a low number.

I purchased a new capacitor on Amazon and received it three days later. Installed the new capacitor and the air conditioner seems to be working fine now.

Just wanted to share.

**creativepart** · 08-18-2021, 07:08 AM

John, shouldn’t you go ahead and replace both Caps while you are at it?

Rossi6998 · 08-18-2021, 11:15 AM

Hi,

I only found one capacitor inside the metal cover attached to the air conditioner unit (which surprised me). I expected to see two of them. There are no additional wires hanging and everything seemed to be connected properly. If there is a second capacitor, it must be in a different location and I would want to replace it too. The air conditioner is a Dometic. Any help would be appreciated.

bigb · 08-18-2021, 01:20 PM

Don't some units have a combination start/run capacitor? Iknow this is the case with residential units

**ThomB** · 08-18-2021, 01:53 PM

Quote:

Originally Posted by bigb

Don't some units have a combination start/run capacitor? Iknow this is the case with residential units

I fully believe that to be a true statement.
When I was researching replacing my start and run capacitors, I did see where one of the manufacturese was using a larger single capacitor. (no, don't remember which).

Rossi6998 · 08-18-2021, 09:19 PM

Well... I am assuming my unit is one of the manufacturers that only uses one capacitor. I would think if it had two capacitors, they would have been located in the same location (inside the metal box attached to the A/C unit). This was a good size dual capacitor (over 4" high and over 2 1/2" wide) with a rating of 60 + 10 uf/Mfd and 370/440 VAC.

https://www.amazon.com/dp/B07VTH4S66...roduct_details

**ThomB** · 08-19-2021, 05:53 AM

I actually have 3 in mine. a Fan, Run and hard-start capacitor.
I'd replaced the fan capacitor when I replaced the fan motor then just recently replaced the run and hard-start when it was blowing warm. The hard-start capacitors are out of stock in many places but I was able to find a Camping World localish to where I was that had the run in stock and when I got there asked about the hard-start. They actually had one that was open and missing parts, but they were parts I know I had so I took that too. Just glad it solved my problem. I didn't want to have to buy a new heat pump.

Bo Walker · 08-23-2021, 03:09 AM

I recently replaced the capacitor on my 2002 Holiday Rambler AC. I couldn't locate one until I ask the old guys that hang out at Hardee's. One guy directed me to his neighbor and the neighbor had one which was bigger in size and had more terminals than I needed. But it had the necessary terminals for my AC. Mine has only one capacitor. It seems strange that the suppliers in Tallahassee didn't have one by part number.

Bobn1957 · 08-23-2021, 10:25 AM

It is not unusual to find dual capacitors in AC units, if there are three terminals on the capacitor it is a dual or combined unit.