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Wednesday, February 16, 2011

Two Motorhome Air Conditioners

I have an older Pace Arrow that has two roof air conditioning units. The front air conditioner will not run (fan or compressor) on shore power. When I start the generator the front unit will work as normal. Any suggestions? Lost for answers! B., (Aiken, SC)

Well Bruce, it’s apparent your motorhome is equipped with only a 30-amp shoreline service. Having a 30-amp limitation basically means that you can only operate one air conditioner at a time while connected to shore power. The reason for this is that, on your Pace Arrow, each air conditioner must be on it’s own, separate 20-amp breaker. So in order to operate all the other 120-volt AC accouterments, you’re limited to only one roof air at a time. It’s simply basic math. 

However, there should be a set of switches somewhere inside your motorhome, (some technicians call them either/or switches), that allow you to choose between the front or rear air conditioner while connected to shore power. The generator, however, is sized large enough to handle both air conditioners at the same time. One air conditioner is hard-wired directly to the generator. On shore power, you must choose which A/C you want to operate. The switches can also be configured to run both A/Cs when powered by the generator (see illustration above)

50-amp coaches do not have this problem since there are 50-amps available on two separate legs of 120-volts. On those RVs, each air conditioner is connected through a different leg. Again, it’s all in the math. 

If it is extremely important to operate both air conditioners at the same time, the only safe and code-compliant option is to install an aftermarket energy management system (EMS), which will automatically cycle each air conditioner, one at a time. Let me know if you cannot locate those “either/or” switches and we’ll dig a little further if necessary.


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