roof top Dometic A/C cycling problem

[carmelo]

Our TT is 5 years old and we have had no problems with the a/c.
Recently it has, on occasion, started cycling on and off rapidly. The only way that we have found to stop it is to turn the unit OFF for a few minutes and then it is OK. Other than that it cools just fine. Filter is clean and it is taking the water out of the air ok.
My wild guess is a thermostat problem but only a guess.
Any one had the problem and fixed it or an idea??
Thanks,
CCC

[DiaperDude]

I am seeing somethimg similar but slightly different out of a 5 year old Dometic rooftop AC where it sounds like it is cycling the compressor even if the unit is switched off. It can be quite load at times. It just started this weekend. The only way I have found to get it to stop is by throwing the breaker. But as soon as you turn it on it starts again. Any thoughts?

[MM49]

Mine was doing that on a +90 degree day. I had the theromstat on auto. I tested it yesterday with the thermostat on manual HI and ran it for 30 minutes without problems. The temperature was lower 76 degrees. When the unit was short cycling it would shut down completely, fan and compressor. The power in trailer was stable, no other electronics flashed.

I re-tested today at 90 degrees. With the thermosat set to FAN HI it ran for 30 minutes without problems. I checked the owners manual online and found that it was designed to cycle BOTH the fan and compressor off and on during the auto mode. This is the exact quote from the manual Auto Fan pg 11.

"When auto fan is selected the fan speed will vary depending on the
difference between the temperature set-point and the room temperature.
In auto fan the compressor and fan cycle On and Off with the
thermostat.
When the difference is:
>5º The fan operates on HIGH
<4º The fan operates on LOW"

mm49

[TomG2]

Did the problem take care of itself this summer? My new unit is short cycling when outside temp is under 85. I mean short cycling, like one minute on, one minute off, and one minute back on for several times in a row. Only thing that changes it, is to set the thermostat a lot warmer or colder than 76 degrees. The only clue that I can give is that discharge temp is in the high forty degrees instead of high fifties like it is on a hot day.

[carmelo]

The unit has done this 3 -4 times. No it does not trip the breaker.
NO it is not freezing up.
I redirected the vents, it is installed with ducting, so that cold air is NOT going direct to the return air and not toward the thermostat. Has not recurred for several days.
CCC

[Charles2222]

Seems Dometic has a problem.Our unit new in 2/14 and this week we got our second replacement.First notice there was a problem when unit started short cycle. Original unit may have had a few hundred hrs,but cecond unit had less than 24 hrs.Good luck. Charles. Above post has some good suggestions

[TInmania]

How rapidly? I don't think it can cycle too rapidly without tripping breaker but that may just be the ones I have experienced.

If it is just short cycling is there a register blowing right on the tstat (assuming it is ducted)? Cold air leaking into intake? Evaporator coils freezing up?



Mike