Author Topic: Low voltage for AC  (Read 5332 times)

Adam Hicklin

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Low voltage for AC
« on: September 01, 2013, 07:34:22 AM »
Although I've read some references to this subject I'm still unclear.  What is the lowest voltage to safely run the AC? I've seen a lot of conflicting info.  Thanks in advance.  

Joel Ashley

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Re: Low voltage for AC
« Reply #1 on: September 01, 2013, 08:30:13 AM »
I think our coach shuts down its landline at 102 volts to protect itself.  Personally I go into concerned and watchful mode when I read 107 volts on either leg.  In that voltage neighborhood I don't like running an AC, and will usually take my meter to the power pedestal to start ferreting out any voltage drop cause, and/or advise the park management.  Certainly, I am at ease at the ideal 119-120 v.

AC pulls max current at startup, like most motors, and if the voltage pressure isn't there to push it the unit will overwork trying to get up to full op.  The result is overheating and a costly failure.  As you may know, a hot day in a full older park can stress resources such that any one site's voltage can be below snuff.

Joel
« Last Edit: September 01, 2013, 08:40:24 AM by 77 »
Joel and Lee Rae Ashley
Clackamas, Oregon
36.9 ft. 2006 Monterey Ventura IV, aka"Monty Rae"
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Gerald Farris

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Re: Low voltage for AC
« Reply #2 on: September 01, 2013, 03:23:34 PM »
Adam,
From most of the literature that I have read, the normally accepted minimum voltage for most circumstances is 104V. Some of the surge/voltage protectors will cut the shore power at a sustained (longer than 2 to 4 minutes) voltage of 102V and others use 104V, but either reading on a sustained basis is time to unplug.

Gerald  

Edward Buker

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Re: Low voltage for AC
« Reply #3 on: September 01, 2013, 04:24:54 PM »
The real issue is starting current of the compressor in the AC unit. The answer in general is in the voltage ranges discussed here and I like to use 107 to 109V as an absolute low limit but there are caveats. The 107V that you see on your panel is 107V at what ever load you are pulling at the moment.  If that is a very light load and you are using a 30 amp cord extension you may drop enough additional voltage during compressor start up to damage the unit. If it was 107 to 109V at the pedestal and you are using your 50amp cord you are better off. Shed as much load as you can to give more current to the compressor, in particular things like the water heater element.

If you are getting 107 to 109V with the air unit running you are probably going to be O.K.  There are some things you can do, Gerald mentioned an autoformer to raise the voltage and if you run into low voltage in the campgrounds that you frequent, that would be a big help.

There are several things you can do to help yourself better tolerate a low voltage condition, first what I would recommend is to lower the thermostat once the air is on so the unit does not kick off and have to restart. These units run on 6 to 10 amps a couple of minutes after start up and are far more tolerant to low voltage while running then when starting.  The second thing is if the unit does kick off or you turn it off wait a good 20 minutes before you turn it back on. There is a small orifice that the freon passes through that over time equalizes the pressure on the high side and low side. The lowest starting current is when the gas pressure has fully equalized. There is a built in timer for this function in order to prevent compressor failure but it is not nearly long enough for a marginal voltage condition. Lastly and most importantly you can listen a few seconds after the fan comes on and see if the compressor fires up without too much struggle, that is more important than any voltage reading guidance, it is what the compressor is telling you. If it is struggling it is best to just shut it down regardless of what the voltage panel reads. Consider going to the generator until the low voltage condition improves.

Under low voltage conditions you are best limiting yourself to one roof air unit or the use of just one compressor in the basement units. Running two is like being a kamikaze pilot and wishing for a soft landing....Hope this helps.

Later Ed

Dennis Crawford

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Re: Low voltage for AC
« Reply #4 on: September 01, 2013, 08:09:00 PM »
Adam,
I assume you mean voltage and not amps.  If voltage, the replies above are good.  If amps, no less than 20  and then only minimum loads elsewhere.

Dennis

Adam Hicklin

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Re: Low voltage for AC
« Reply #5 on: September 01, 2013, 11:33:27 PM »
Thanks guys.

Yes Dennis, I was talking volts.  According to your replies I'm in good shape.  The park I'm in at the moment is reading 108+ volts on each leg with the AC running. Usually 111-117 range with nothing on.  I have been listening to the compressors like Ed suggested and they sound normal and don't struggle at start up.  I seldom run the AC but it is hotter than Hades here. Typically this park is pretty good power wise, but it is maxed out for the long weekend and everyone is running AC!

Thanks again.