Saturday, December 9, 2023


Ask Dave: Why does distribution panel buzz and spark with two ACs?

Dear Dave,
I have a 2002 Southwind 30 amp. Is the back AC supposed to run only off the 20-amp breaker, off the generator? I turned the 20 amp on and it would run the front air but nothing else. Then turned the 20 amp off and the 30 amp on, and it would run either the front or rear AC, microwave, etc. If I turn on both air conditioners with both breakers on, the solenoid behind the fuses buzzes and sparks and it kills the generator within a few seconds. It used to run both fine. —Kellie

Dear Kellie,
First, DO NOT try to run both roof air conditioners! Have the distribution panel inspected by a qualified technician ASAP. If you have had buzzing and sparks, this is dangerous!

Now, I am not sure what “breakers” you are referring to. However, I’m guessing you have a 30 amp for the front roof air conditioner in the distribution panel and a 20 amp for the rear.

What could be happening behind the breakers

Typically, the bedroom roof air conditioner is a smaller BTU, therefore, the 20-amp breaker. If you are flipping both breakers on and running both roof air conditioners only when plugged to shoreline power, you will be overloading the circuit. That is what I assume is happening behind the breakers.

Normally, the system should only allow one roof air conditioner to be used at a time on a 30-amp power source. There should be a switch in an upper cabinet that is labeled front and back. It’s not impossible to run two roof air conditioners on a 30-amp circuit. However, each could draw up to 14 amps and possibly more if there is an issue with the compressor. If your unit does not have the switch, it’s possible that it was rewired at some point, since it’s a 2002.

A safe way to run two ACs at one time

The safe way to run both roof air conditioners at one time is to use the generator. I would assume you have an Onan generator, probably 5000 k or larger, which has two circuit breakers on the generator.

The 30-amp breaker provides 120-volt/30-amp power to your distribution center inside the rig.

The 20-amp circuit breaker should be wired directly to the rear air conditioner. The only way you are supposed to be able to run both roof airs is start up the generator and have the switch pointed to the front label. This means 120-volt power is supplied to the front roof air by the distribution center, and the back air is powered by the 20-amp line from the generator. Placing the switch on the rear label provides 120-volt power from the distribution center to the rear roof air conditioner. This should be done only if the generator is not running and the shoreline power is plugged into a campground source.

Why did both ACs run previously?

So, why did it run both roof air conditioners in the past? There are several power factors that can come into play such as what other appliances were running at the same time in the past. Were the refrigerator, water heater, or other components running? Also, as the units get older, the compressors start to draw more amps, especially if there is an air flow issue. If the front evaporator coil is clogged, or the filter, the motor and compressor will work harder to draw in air and the amps go up. I would suggest having both looked at and cleaned.

This is an AC unit that had talcum powder caked to the evaporator coil and ruined the unit.

One thing you might want to do is add a SoftStartRV device that will help monitor the amp draw. Here are articles that Chuck Woodbury and Dave Helgeson wrote about it.

However, it is important to have someone take a look behind your distribution center before going any further!

Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club.

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Dave Solberg
Dave Solberg
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.



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Bob p (@guest_166608)
1 year ago

I had a ‘99 Bounder with 2 A/Cs and the circuits were set up with some kind of switch that would run 1 A/C then the other, alternating between the 2. I didn’t understand the theory but it worked and kept the unit cool. It was strictly 30A service.

Dennis (@guest_165915)
1 year ago

I have a Forest River 30′ class A with only one a/c unit. As Dave says: that unit’s power is supplied by the 30 amp breaker on my genset. (Generac Q-55G) I do a lot of winter camping so I had a 20 amp outlet hard wired to the genset’s 20 amp breaker. This setup allows me to run 3 Pelonis 1,500 watt disc furnaces all at once plus the fridge. One Pelonis is on the genset 20A breaker, the second Pelonis is plugged into the GFCI outlet and the third Pelonis is plugged into the regular house circuit. My house breakers are 15A each so that would not work for any 2 Pelonis heaters at once. (12.5 amps x 2 = 25 amps = tripped breaker) Been doing this for years and never tripped a breaker on genset or distribution panel. That’s 15,345 btu being pumped into my coach. Very cozy and uses apx .8 gallons per hour.

tom (@guest_165909)
1 year ago

Sparks bad news.

Jesse Crouse (@guest_165907)
1 year ago

Like Dave said-DON’T RUN BOTH A/C’S.

Bill (@guest_165942)
1 year ago
Reply to  Jesse Crouse

Like Dave says “see a qualified technician” NOW!

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