A/C "Short Cycles" repeatedly.

Creativepart · 07-14-2015, 04:25 PM

We are on our first "shake down" trip with our 3051s Forester. 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 every 8 to 10 mins non-stop.

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.

After 90 mins or so of this I turned the unit off at the thermostat, waited 6 mins to relieve compressor pressures and restarted the unit.

So far it has not started in the hour or so since we turned it back on.

Any A/C knowledgeable folks care to offer any help or advice?

bigdaddy1 · 07-14-2015, 08:28 PM

I have the Dometic A/Cs a 13.5k in the front and 15k in the rear of my 3850RL fifth-wheel Cardinal and I am having the same deal going on with the short-cycles. If I have the control set with the fan on auto and set temp at a comfortable level once it gets to set temp it starts the on and off cycling until I change the fan setting to HI then no problem but I have to shut unit down instead of being able to have the unit work as it is designed. This is a new camper built this spring so I will get this taken care of soon.

LSUTiger · 07-14-2015, 10:02 PM

I have a 13.5 up front that short cycles as well. It appears that this problem has risen numerous times on this board.

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Crisg1 · 07-15-2015, 06:45 PM

We have same issue with Dometic Roof AC in our 2015 Columbus 375RL .. Not a happy camper...

Alexha · 07-16-2015, 12:49 PM

I've had (still have) the same problem (AC/Furnace short cycle) in every RV I've ever owned. The wall thermostat is often located directly in the air output path of the AC/Furnace unit - there seems to be no way to avoid this in most RV's because of limited wall space. If you can, redirect the airflow away from the thermostat using the adjustable output vents, it can help. I've also found that using a small external fan can help prevent temperature layering of the air. Try taping a paper air deflector over the top or sides of the thermostat (be sure not to block it completely). If none of these quick fixes work it may mean you have a more serious A/C problem requiring professional repair.

hillsdaletc · 07-16-2015, 12:51 PM

If your in a high humidity situation you could be freezing up at the evaporator. The sensor will shut down the compressor till it senses the ice melting off into the drain pan and will then cycle back on. The warmer outside ambient temp. the faster the ice dissolves and the quicker it recycles. Just a guess at your situation.

mike2wheels · 07-16-2015, 04:57 PM

The 15k unit over the kitchen/living room does this if I leave the thermostat set to "AUTO" fan control. If I change the fan control to "HI" we don't have this problem.

danmer · 07-16-2015, 08:01 PM

Hi guys, make sure all your vents are not directed to the area where the thermostat is installed, that will create a short cycling. The thermostat is sensing the cold air coming out of the vents and the compressor will go off, and that will be happening over and over, that's called, short cycling. Hope this information help you all. Dan

siskom · 07-17-2015, 08:54 AM

Advice here is good for short cycle... it drove us crazy in bedroom had to close vents closest to thermostat. in living area had to make sure bathroom door did not swing open and hide thermostat because it would never shut off.

B and B · 07-17-2015, 09:02 AM

Some of the short cycle may be related to the position of the freeze sensor. It might be cutting out too early causing short cycling.

Creativepart · 07-17-2015, 09:42 AM

When I first posted this question I hadn't paid close enough attention to the duration between short cycles. It seemed like it was 5+ mins maybe. But the next time it started doing it my wife used her phone to time it. The time between short cycles was between 1 min 07 seconds and 1 min 40 seconds.

That's the air conditioner stopping to a full-stop every min and restarting and doing it over and over and over again. And, while the fan is most noticeable when it stops it's also true that the compressor is kicking in on the restart 1 second later.

I can understand that the unit could freeze up - and shut down to thaw the coils. But why would it only stay stopped for a second or two before restarting. So, I don't see how it could be that.

I can also understand that if a vent is blowing on the thermostat that it could prematurely tell the A/C to stop. But, I don't see how it could do this once per minute for 90 mins.

Plus, neither the freezing nor the vent blowing on the thermostat would explain why the problem goes away when the unit is set to LO or HI.

It must be that either the thermostat on the wall has a problem or the control unit in the A/C has a problem.

LSUTiger · 07-17-2015, 05:22 PM

I dug this old topic on this discussion from an earlier post where we discussed the same thing.

http://www.forestriverforums.com/for...ing-29650.html

NeilM108 · 07-17-2015, 05:23 PM

1. Agree that it is a good idea not to have any of your A/C vents directed at the thermostat.
2. If compressor and fan are cycling a lot, make sure you haven't set the one degree (vs 2 degree) differential on the thermostat. This will drive you crazy.
3. If the fan stops momentarily but the compressor quietly continues to run, this is how the fan changes speed (moronic as it that is!) and is normal.

I'd love to find an alternative to the Dometic digital thermostat, but the interface appears proprietary.

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