Making Your Air Conditioner Generator Friendly

June 7, 2009 by Mark Corgan · 11 Comments  
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Some RV air conditioners have a difficult time starting when using a generator, especially portable generators. There are a number of factors that contribute to hard starting but most often it’s because there is not enough available power to start the compressor quickly. The compressor motor in a typical RV air conditioner system can draw a tremendous amount of current during it’s start-up time. This can be as high as 50 amps for a typical 15,000 BTU A/C on a hot day. All but the largest of RV generators can struggle to provide this kind of power without significant voltage droop. Not having enough voltage and current to start the A/C compressor, the generator goes in to overload and pops it’s circuit breaker. What can be done to help this situation? Modify your RV air conditioner with a hard start boost capacitor.What is a hard start boost capacitor you ask? It’s an electrical device that is added to your A/C system to provide a short term power boost that assists compressor starting. The capacitor stores electricity and provides it all at once when the compressor is starting. Most newer RV air conditioners may already have a booster capacitor, but they tend to be a bit undersized. So even those that do have them, can still benefit from this mod.

A typical RV A/C provides 13,500 BTU of cooling, and generally requires a generator that has a minimum surge rating of 3500 watts. Many of the popular portable generators, such as the Honda EU2000 or the Yamaha 2400i, cannot provide this level of surge power. Many folks have tried starting their A/Cs using these generators, and while a few have been successful, most have not. Those that were successful likely had a boost capacitor installed.

If after installing a boost capacitor you still have start-up problems using a small generator, here are a few tips that can help get your A/C going.

  1. Turn off all AC breakers except for the main power and A/C breakers. This ensures that the battery charger and no other AC accessories are demanding power and thus reducing available start-up power to the A/C.
  2. If your generator has an economy switch, be sure to switch it off economy. This ensures the generator is at it’s highest speed which can provide the required power more quickly.
  3. If tips 1 and 2 don’t work, there are 2 possibilities: your generator is too undersized even with a boost capacitor, or you are at too high of an altitude. Generator power decreases by around 3% for every 1000 feet of altitude. If you are at 5000 feet, then your generator will produce 15% less power. That might be just the missing amount you need to get the A/C compressor going.

I personally use a Kipor KGE3500i inverter generator which has a surge rating of 3500 watts and a run rating of 2800 watts. At high altitudes, I have to switch the economy switch off or my TT’s 13,500 BTU A/C will refuse to start. And I have a boost capacitor installed! Only at sea level will the generator start the A/C on economy.

For more information, tips, pictures of how to install a hard start boost capacitor, and where you can buy one, head on over to and have a look at this article:

Happy modding!

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11 Responses to “Making Your Air Conditioner Generator Friendly”

  1. Dave Planitzer on June 7th, 2009 1:37 pm

    Another helpful hint: Don’t have the fan switch set to auto. Set it to always run that way the fan motor will be running already when you switch on the AC and there will be only the compressor motor to start rather than two motors to start at once.
    I can run my 13,500 AC with my Honda 2000 with all other electrical loads turned off as mentioned.

  2. Keith on June 8th, 2009 10:16 am

    I wouldl love to do this mod but need help on how to identify what is needed and where to buy as the link that was provided was not able to assist in the part.

    Any help is appreciated.


  3. Mark Corgan on June 8th, 2009 8:16 pm

    @Dave – That is a very good tip Dave! I usually start the fan blower on low speed first, letting the generator stabilize, then switch on the A/C to low cool. If I need more cooling, I switch the fan to high speed. This helps a great deal when running the A/C off of a small generator like the EU2000.

  4. Mark Corgan on June 8th, 2009 8:19 pm

    @Keith – Which link are you referring to? If it’s to, look at the article comments. There is a link the shows where to buy a hard start cap. I bought mine through that site and the cap came with wiring instructions showing a few different possible A/C configurations.

  5. TT addiction on August 18th, 2009 1:38 pm


    Perfect mod at the perfect time for me. I was headed out to get a 2nd Yam EF2400iS when I came upon this mod. I have a Rockwood 2501 with a 13.5K ac. It would start up but stop after just a moment. The weather in the central valley in summer is very hot at times and the ac was essential. Read this mod and installed the Sup6E. Turned the gen on then the ac. It worked beautifully and stayed on for as long as I needed. I could use lights and the water pump simultaneously. This saved me 1K plus for a 2nd generator. So thankful for these mod’s.


  6. lttlfeller on October 29th, 2009 10:46 am

    Great information! I want to share my experience with this mod as it worked great. I recently bought a new 5th wheel with a Coleman Mach-air 15,000 btu A/C and I have a Yamaha EF2400i generator. My generator would not start the A/C before installing the hard start kit. I used the Supco SPP6 (not the 6E) because that is all I found locally. When I opened my A/C I discovered it did not have a start capacitor. I connected the SPP6 to the run capacitor which was very simple. Now my EF2400i starts and runs the A/C with only moderate loading. It seems like the generator even runs the 15,000 btu A/C easier than it ran our old 13,500 btu A/C. I’m very pleased with this mod… thank you!

  7. chad jones on November 30th, 2009 9:30 pm

    keep in mind if your Gen-Set has a hard time starting the AC and you need the AC to keep cool that that size AC will most liky over heat . you need to have a little more capacity than your using to keep the Gen-Set running good , if you running at MAX Cap it wont last

  8. chad jones on November 30th, 2009 9:33 pm

    I mean the Gen-Set may over het after a while

  9. Joseph Earle on May 2nd, 2012 5:46 pm

    Why not connect the capacitor on the Line input side of the main breaker panel so all Load outputs could use the temporary storage and shock absorbing capacity of the capacitor?

  10. tim @ ac capacitor on June 20th, 2012 2:51 am

    Thanks for this informative posts. i also have some hvac related posts in my site. but not detailed as this one. thanks again.

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    How much would it cost me to create a web site I purchased on GoDaddy for instance into
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