Dometic AC unit

May well be normal. AC fan runs on high until it reaches set temp. Unit shuts off and comes back on with fan speed on low. Cycle can continue several times especially when temps are high

I would try using a different ceiling assembly, which has the controls in it, and see if that correct issues.
An RV seller is ill-equipped to do any meaningful repairs and unlikely they have the ability to delve into refrigerant levels or pressures.
If you could check the coolant levels that would be great. I am not sure these roof ACs allow you to check as you would on a car or a house.

All AC units are basically the same, so a guy that can work on an AC will be able to work on any AC.

Is your compressor actually running, or just trying to start and giving up? You will hear the strain as the compressor tries to kick on, and then it smooths out a little when running. A 10 second cycle will not work on any unit. After the compressor kicks off the system needs time for the pressures to euqualize inside the pipes. The high pressure side will have too-high of pressure for the compressor to overcome and start. This is why you not supposed to turn temp up (making compressor turn off) then turn temp back down seconds later. Compressor will struggle to start, it might start, but that struggle is bad for the compressor.
On that note, there could also be an issue with your 2-stage starting capacitor. losse or coroded wires, bad capacitor...lots of youtube videos on this.

brnthumbinfl wrote:
We purchased our 2019 Mesa Ridge 21RBS TT from Lazy Days in Tampa, January 2019. We've had it in twice for warranty repairs. Both times, we reported the AC unit would hover when it reached the set temperature. Particular at night, the unit will cycle on for as little as 10 seconds then cycle off for 10 seconds. Back and forth as many as a dozen times. The unit is not terrible quiet, so this gets irritating when you're trying to sleep. Plus it can't be good for the unit.

Lazy Days checked it twice without finding anything wrong. Of course it was winter when the unit isn't really working. They tried insulating the thermostat, then I forced them to replace the thermostat. Neither action corrected the problem. Currently I am beginning to think it may be the unit itself. It seems when it goes into hover mode, I'm not sure its really cooling as the air seems just room temp.

Any ideas?

Brnthumb

Are you sure it is doing it a "dozen times"
If you read your manual, you'll find out that it is normal and is adjusting itself to a lower speed once it reaches the set point.

Guy

brnthumbinfl wrote:
...the unit will cycle on for as little as 10 seconds then cycle off for 10 seconds. Back and forth...

Perhaps it is the differential temperature setting - see LINK

Where is the thermocouple? Pull the panel off, and make sure the thermocouple is in the air flow. I bent mine about 30 deg forward into the airflow and it works perfectly now.

Mine has done similar when fan is on auto. Set to either low or high.

Hoping someone comes on with the real answer. Mine does the same thing when the temperature outside is only a few degrees warmer than inside. I suspect it is some kind of "feature" that is supposed to keep the AC from freezing up or hurting itself. Any technicians out there?

TomG2. Now that you have tried all the above suggestions, just let us know you have, and then we will offer the real answer. There can be only one answer. No one has ever had an issue and solved it by other means.

ajriding wrote:
TomG2. Now that you have tried all the above suggestions, just let us know you have, and then we will offer the real answer. There can be only one answer. No one has everss had an issue and solved it by other means.

Thanks, but I am not the OP, just following. This is the third AC unit to do this for me, so I am curious. For now, I simply turn it off in the early morning hours. As far as trying all the suggestions, I will leave that to others. I did not even know that Air Conditioners had a "Thermocouple".

If you have the "Real" answer, many would be glad to hear it.

Thermocouple is the bare copper wire (tube) with the big end (about pencil thickness) and is a thermometer for the AC to measure incoming air. Just to clarify if any readers wonder.

If you have issues and want to fix, then really try the suggestions. There will be no real answer, that was kidding, all answers are possible to be your issue or not. If you do not try to solve, then it wont fix itself.

Even professional auto mechanics try suggestions. They start with the easy thing, charge you, then move on to more and more complex and expensive things to see if it will work, all the while charging you for their attempts. If you can do it yourself for free then saves money. Process of elimination. You have to try the fixes known to cause issues.