Why won’t RV’s AC work on generator power?


RV Doctor

Dear Gary,
I have just borrowed a 29-foot motorhome to drive to a NASCAR race. The air conditioner works wonderful when using the extension cord and running off my electrical power but it doesn’t work at all when the generator is on. Is there a switch I must throw to get it to convert from extension cord to generator? —William J.

Dear William,
Typically, to get the AC electricity produced by an on-board generator to power the RV, it requires one of two methods. The first is automatic: An automatic transfer switch (usually with a time delay) senses the presence of voltage produced by the generator and automatically energizes the panel-board distribution panel in the RV and prohibits further input from the shoreline cord. Motorhomes are wired so that two different sources of 120-volt AC electricity cannot feed the coach at the same time. The automatic transfer switch provides that methodology for both the hot and the neutral power conductors.

The second process of getting generator power to the rest of the rig is by manually plugging the shoreline into a dedicated receptacle wired directly to the output of the generator. In other words, to get AC power to the RV you must plug the shoreline cord somewhere – either into an electrical source such as a campground pedestal or into the generator receptacle. It’s usually located inside the same compartment as the shoreline cord.

Pull the shoreline cord all the way out and look inside that compartment with a flashlight. I’m guessing you’ll see a 4-inch square box with a 30-amp female receptacle. Be sure all loads are turned off, then plug the shoreline cord into that receptacle and start the generator. If all the breakers are set properly, you should get power to the coach. Of course, you may have a problem with the transfer switch itself if your coach is so equipped. But that’s a whole other issue!

And depending on how old that motorhome is, there is a third method of obtaining generator power that mandates the user flip a set of circuit breakers. The older GMC motorhome had such a setup at one time. The user had to manually flip the breakers from shore power to generator power.

Also keep in mind all RV generators are protected by an integral set of circuit breakers located on the generator itself. It is possible everything in the motorhome is fine but the breakers on the generator itself may be tripped. Look on the generator and be sure its integral breakers are in the “on” position.

gary-736Read more from Gary Bunzer at the RVdoctor.com. See Gary’s videos about RV repair and maintenance.



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Kandice Roth
5 days ago

Thanks Gary! We had the same problem with our toy hauler and you helped us!

11 months ago

Although I appreciate the article, it seems there are some questions that may have not been asked. Are any other Alternating Current items working in the RV when the generator is running? If so, it could be a system bypass for the Air Conditioner. They use lots of power mostly for the starting in-rush power needed.