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Old 07-14-2015, 04:08 PM   #1
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After 5 or so hours of use A/C unit "short cycles" repeatedly

We are on our first "shake down" trip with our 3051s Forester. We're in southwest Texas and it's 97 degrees every day. A couple of times yesterday the A/C unit (running pretty much non-stop) short cycled ones or twice.

Then today it started doing it around noon time and did so every 8 to 10 mins for about 90 mins.

Here's how it acts when it short cycles. The fan stops and 2 to 3 seconds later the compressor start-up kicks on and the unit runs normally for another 8 or so mins before it does this again.

I was going to let it do it continuously until the A/C just stopped working but my wife complained. So, we took a PC repairman approach to the problem and turned it off at the thermostat.

I know little about A/C units but I know to wait 5 mins to let the compressor head pressure reduce before restarting - so we set a timer and turned the A/C back on after 6 mins.

So far it has not short cycled once for the past 90 mins.

We did notice that it displayed this same behavior once or twice the day we picked up the RV and again once or twice at home in the driveway while we were packing for this trip.

Each time its VERY noticeable since it's running non-stop to have the fan stop and then restart.

I can't see taking it to the dealer, because he'll just turn it on and say "it's running fine now."

Last month I stayed at a hotel on a trip. It had one of those thru the wall heat pumps you see at most motels these days. It started doing this exact same thing. I called the front desk and they sent a man. I explained what it was doing and he said, "Ok, that's short cycling. We'll bring up a new one."

A few mins later he showed up with an A/C unit on a dolly, pulled out the short cycling unit and replaced it in minutes. He said, "They do this all the time and there is no way to fix it without rebuilding the compressor pump. So, we keep a stock of rebuilt units in the shop so we can swape them out."

Not sure who to call with this unit doing it intermittently.

Any ideas?

PS. I say it's running non-stop - but it does stop for a while in the middle of the night. It's 80 here at midnight, but 70 around 4 am. So, the A/C does stop for a couple of hours during the night.

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Old 07-14-2015, 04:30 PM   #2
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Could be freezing up. Let cool off then see what happens. Later RJD

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Old 07-14-2015, 05:30 PM   #3
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Actually this may be normal. It's sounds like the compressor is staying running but the fan is switching from high to low or vice versa. If it's a few degrees away from set point the fan is on high. As it closes in on thermostat set temp it will momentarily stop the fan and then switch it to low. Most times the low will finish out the cycle and satisfy the stat but I have seen where it didn't and the temp in the rig rises so it then again pauses and switches back to high.
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Old 07-14-2015, 05:37 PM   #4
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Is the fan set to 'auto' or 'high' ?
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Old 07-14-2015, 05:41 PM   #5
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it might be changing fan speeds. It shuts off for a few seconds when it does so
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Old 07-14-2015, 06:10 PM   #6
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my AC does the same on my 2005 CC RL, runs for a while then it will start to cycle the compressor. but the fan will stay running.
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Old 07-14-2015, 09:00 PM   #7
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This is a little annoying when it keeps switching like that. If it's very hot during the day I switch mine to hi and just let it run like that till the evening and switch it back to auto.
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Old 07-14-2015, 09:09 PM   #8
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It's possible that the unit is intentionally tripping off due to low supply voltage. Somewhere around 108 volts is common. Of course, this is more likely in hot weather due to brownouts. Monitor the incoming line voltage and see if it's dipping.

Second item is the thermostat. Most are microprocessor controlled, and sometimes need a reset. Just disconnect the power for a few minutes.
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Old 07-14-2015, 09:11 PM   #9
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iv'e never tried yet on a 50amp only 30amp.
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Old 07-14-2015, 09:16 PM   #10
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What model thermostat do you have? Have you read the manual? So far as I'm aware, the fan is strictly controlled by the thermostat, NOT the A/C.

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