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Old 06-29-2016, 12:58 PM   #1
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Question about running AC's in extreme heat

Hello all,

Last week we were driving across the Imperial Valley area in the record 118 degree heat. Needless to say, that kind of heat pushes everything to its limits. We have a 10K generator that never shut down during the heat but it would blow the 45amp breaker on the generator if we ran all three roof AC's. So we switched the fridge over to LP and only ran the front roof air and never had any further issues.

I was told that in that kind of heat, the AC's pull a lot more amps than they normally do and so there is no chance of running all three off the generator. The example I was given was that normally they each pull about 12 +/- amps but in extreme heat that number could be as high as 19 amps. I was also told if we were parked, we would have the same problem with 50amp shore power in heat above 110 or so.

My question - does this sound correct? Obviously our goal is to stay out of that kind of heat but hey, we live in Phoenix so getting out of town in the summer can be hot until we get to higher ground or the beach! Additionally, we usually fire up the RV about 48 hours before we hit the road to load it, get the fridge cold etc so it would be nice to know my limits on power consumption in our summer heat. Our previous coach had 50amp service but only 2 AC's so we never had a problem.

Thanks for your input.
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Old 06-29-2016, 01:14 PM   #2
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Yeah, heat can put a strain on the systems.. but I would think you could run two a/c no problem
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Old 06-29-2016, 01:14 PM   #3
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Something doesn't sound right. First, not sure why the A/C would pull more just because it is hot outside. Second, even of all three A/C pulled 20 amps each (not likely) that would be only 60 amp total. Your generator puts out two 45 amp legs for a total of 90 amps.
On shore power the 50 amp service Has two legs of 50 amp each for a total of 100 amp. More that enough to run everything in your coach at the same time.
Not sure what is wrong but something is not right.
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Old 06-29-2016, 01:25 PM   #4
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Originally Posted by Selah View Post
Something doesn't sound right. First, not sure why the A/C would pull more just because it is hot outside. Second, even of all three A/C pulled 20 amps each (not likely) that would be only 60 amp total. Your generator puts out two 45 amp legs for a total of 90 amps.
On shore power the 50 amp service Has two legs of 50 amp each for a total of 100 amp. More that enough to run everything in your coach at the same time.
Not sure what is wrong but something is not right.
I have seen 20 amps on my AC, before I cleaned the coils on the roof. It was only in the high 80s that day.

The hotter the ambient air, the higher the refrigerant pressure. Higher pressure equels more current draw.

Although there is 90 amps, 2 of the AC units must share a 45 amp leg.

If anything else is running, that puts them close to the threshold of the breaker.
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Old 06-29-2016, 01:32 PM   #5
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And don't forget the Refrigerator. It probably has the same additional draw in heat as the A/Cs
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Old 06-29-2016, 02:58 PM   #6
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Never seen our Very High Efficiency A/Cs pull over 8 amps each. Even extremely hot out. With 3 A/Cs it should never pull more than our 8K water cooled generator can produce.
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Old 06-29-2016, 02:59 PM   #7
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And don't forget the Refrigerator. It probably has the same additional draw in heat as the A/Cs
Exactly! That's why I mentioned that we switched it over to LP.
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Old 06-29-2016, 03:00 PM   #8
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Originally Posted by twinboat View Post
I have seen 20 amps on my AC, before I cleaned the coils on the roof. It was only in the high 80s that day.

The hotter the ambient air, the higher the refrigerant pressure. Higher pressure equels more current draw.

Although there is 90 amps, 2 of the AC units must share a 45 amp leg.

If anything else is running, that puts them close to the threshold of the breaker.
That is how I understood it when it was explained to me.
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Old 06-29-2016, 03:02 PM   #9
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Quote:
Originally Posted by Fiesta48 View Post
Never seen our Very High Efficiency A/Cs pull over 8 amps each. Even extremely hot out. With 3 A/Cs it should never pull more than our 8K water cooled generator can produce.
I have never had a problem with ours in in the past. However, I have never been running all three in 118 degree heat before this. 105, yes. 110, yes. Never 118.
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Old 06-29-2016, 04:49 PM   #10
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Any appliance, AC, Refer, Range, Dryer etc should never draw more current (amps) than the listing on the label.
If it does it should shut down or trip the breaker.
This is a UL listing thing !!!!!!!!!!
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Old 06-29-2016, 04:55 PM   #11
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A properly working A/C shouldn't draw more amperage than the label states it will draw. A dirty coil or failing compressor could cause the current draw to go up. You may have an issue with one of your A/Cs.
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Old 06-29-2016, 05:00 PM   #12
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Quote:
Originally Posted by Selah View Post
Something doesn't sound right. First, not sure why the A/C would pull more just because it is hot outside.
The hotter the temperatures the hotter the refrigerant is this means it take more power to compress it the same hence higher load.

For instance the Coleman Mach 15 on my RV is rated to draw 1650 watts at 95F outside and 1900 watts at 115F outside.

Temperature most definitely effects amp draw.
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Old 06-29-2016, 05:02 PM   #13
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Quote:
Originally Posted by Selah View Post
On shore power the 50 amp service Has two legs of 50 amp each for a total of 100 amp. More that enough to run everything in your coach at the same time.
Ours will draw more than 100 amps if I turn everything on but our dryer is 220 volts.
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Old 06-29-2016, 05:07 PM   #14
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Quote:
Originally Posted by Dutchstar08 View Post
Any appliance, AC, Refer, Range, Dryer etc should never draw more current (amps) than the listing on the label.
If it does it should shut down or trip the breaker.
This is a UL listing thing !!!!!!!!!!
No need to yell.

Each AC unit is on its own 20amp breaker so I will assume they are rated up to 20amps. None of those tripped so I will assume that none of the individual AC's ever exceeded 20amps.

And...based on my description in my initial post, the breaker on the generator did properly trip when the three AC's running together exceeded the generator's max load.

This is what lead to my question of - Could the excessive heat cause each AC unit to increase its load enough(but still be within it's acceptable operating range) that when all running together, they exceed the generator's capacity?
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