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Old 07-12-2004, 04:08 PM   #1
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1967 26' Overlander
Huntsville , Alabama
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Best voltage for A/C?

Air conditioners draw a lot of current. If the service is not suitable, a voltage drop will occur as the wiring tries to keep up with demand. Before testing my repairs on my original Armstrong air conditioner unit, I checked with an electrical engineer I hold in high regard as to what the minimum voltage the compressor & fan motors should see before deciding the shore power is unsuitable, and turning the A/C off. He indicated 110 vac should be the minimum line voltage for running any given motor.

Parallel to me fixing my unit, I have been keeping another friend posted on my efforts, and what I am keeping in mind as he works to bring his Airstream’s non-OEM unit out of a three or more year retirement.

For me, so far so good. For him, his fan motor quit today after, let’s say no more than four hours of operation at no less than 112 volts. I am pretty comfortable with the 110 vac minimum - coupled with what I know about motors, it sounded good.

While his motor failure may be due to something else, what is your opinion of minimum voltage for running an air conditioner?


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Old 07-12-2004, 04:31 PM   #2
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Corona , California
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Minimum Line Voltage

110 VAC is an absolute minmum voltage required to run the typical RV roof AC.

However, if the voltage is 110 and nothing else is on, then that's what your stuck with, namely, nothing else can be turned on.

Therefore it is far superior to have at least 120 VAC at the trailer, with the AC running.

That will allow you to turn other things on as well.


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Old 07-12-2004, 06:10 PM   #3
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The State of , Ohio
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I found a copy of the Duo-Therm Service Manual on-line at Bryant RV.

On page 3, it says that the air-conditioner is a 115 VAC device and the proper operating range is between 103 and 126.5 VAC, but that voltage should be taken at the unit power supply leads (to include the voltage drop of the house wiring going to it). Remember that from the campground power pedestal, where you may be measuring voltage, there's voltage drop across about 30' of 10AWG cable to the breaker box, plus that on maybe 15'-20' of 12AWG cable from the breaker box to the AC unit.

What it doesn't say is that any AC voltage measurement should be taken with a quality RMS voltage meter.

Whether I'd run the air-conditioner with pedestal voltage as low as 108VAC RMS would really depend on whether I could get through the night reasonably comfortably with the Fantastic Vents.

Of course, if you have two Honda EU2000s in the truck bed, to get you through the night until you can find another campground, low campground voltage isn't an issue!
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Old 07-12-2004, 08:09 PM   #4
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standard voltage


here at the power company we try to serve our customers with 120/240 volts + or - 5%.

most distrubution transformers i hang are set a little high, usually 127 volts or so. this allows for line drop on the service coming into your home.

remember to check your voltage as close to the load as possible, AND while the load is running. if you check voltage without the current draw you will get a "false" reading.

if you are at a campground with bad electrical service do as moe suggests JUST LEAVE! and tell the owners why.

some folks i know just spent 60k to upgrade the elecrical service at the campground they own. they did it to keep the campers happy! they are full almost year round!

you call them ferrets, i call them weasels.
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