Yet another AC question

[Smitty8934]

I've had a similar problem which I posted. My front air works as it's suppose to. Fan on hi or low fan runs continuously with compressor cycling. On auto both fan and compressor cycles on or off. Now the rear unit has the problem similar to yours. On fan hi the fan will run continuously with compressor cycling off and on. On fan auto, both cycle. Now here's the problem, on fan low the fan and compressor both run and then once the temperature is reached the entire unit shuts down. I need to cycle thru the system to turn it back on and then I forget about using fan low due to this problem. I have the two thermostat system. I may try switching the thermostats and see if this works.

[Rex-]

I have been trying to find the right thread to post my issue, maybe this is it. We have a 2016 3791 that has had ac issues since we first used it in 6-16. We have two ac's each operated by their own stat. The units will start and cool fairly good for a while then for no explainable reason the compressor will cycle off for a few seconds and then right back on, or the fan will cycle off and right back on, then maybe the compressor again. Each time either one is off for just a few seconds and they do not cycle together. Then it may run just fine for awhile. I have spent over 40 years in the industrial refrigeration field so I understand the mechanical and electrical side of an ac unit although I'm certainly not an RV ac expert. These are fairly simple units with just a few electrical components so when it started acting up I replaced the stat believing that to be the issue, no change. Then I replaced the circuit board in the condensing unit, again no change which really surprised me. After the season we pulled it out of our permanent spot and took it into our dealer. They had it for a few weeks, talked to Dometic a few times and "hoped" they had it fixed although they couldn't tell me exactly what they did to fix it. Although they did assure me that even though the one year warranty would expire before the next season they would still cover the problem as it would be considered an ongoing issue that was identified during the warranty period. We took it out this year and of course no difference. The compressor and fan continued to cycle erratically. We took it back to the dealer in July 17, they had it for a couple of weeks and even with Dometic's help and a couple of conference calls with the dealer, Dometic and myself they still could not find the problem. So Dometic sent two new ac units and the dealer installed them. We took it back to our camp site and believe it or not, still no change. Both continued to cycle. Let me also explain that this happens even with the stats set at their lowest setting and the coach at mid 70's and higher. I also do not believe it is freezing up as the compressor cycles right back on and I have not noticed any drop in cfm's out of the vents. TD has been around 28-30+ degrees which does indicate a lack of adequate air flow. So now it is back at the dealer, who has tried unsuccessfully to get a Dometic tech out to help find the problem. The general manger has gotten involved and called Montana and now a Montana rep will be here Monday to look at the unit. If he can't figure it out he said he would have it pulled back to the factory where there have both Montana and Dometic techs on site. I will also say that even though the dealer, RCD in the Columbus Ohio area, has not been able to ID the problem they have always been very accommodating and persistent in fact that they are committed to seeing this issue to the end. After hearing so many nightmare stories from others about their dealers I feel fortunate to be dealing with a company like RCD. Tim the general manager, Trish the service manager and Matt the assistant service manager have all I believe done all they can and are equally frustrated with this issue.
Has anyone had this issue or heard of an issue like this? And if so was a resolution found? Sorry for such a long posting.

[kdeiss]

Just like to mention a couple things. Dometic AC units have a two year Warranty at least they did in 2014. The Unit will cycle on and off when in Auto Fan from Low to High or High to Low depending on the units ability to satisfy the thermostat.
Also I might what to mention their is a freeze sensor that should be placed between the evaporator coil low on the left side as I remember in my case it was laying in the drip rail with no evidence of being installed in the evaporator coil. The purpose of the sensor is to ID a freeze and turn the compressor off and leave the fan run to thaw the coil.

[Rex-]

Thank you for your comments. I think you are correct about the two year warranty. Also while testing the ac I would set the stat setpoint very low to prevent the fan from its normal cycling. This problem is beyond frustrating!

[lilpeach]

Just wanted to chip in about RCD RV in Sunbury, OH. I too bought my 2017 Montana from them. I had a 2016 High Country that I bought in New Mexico. I was in Ohio when I needed warranty work. I called and got an appointment 4 days after calling. They didn't have a problem about my not having bought that unit from them. Matter of fact I didn't know that was an issue with dealers. Matt in service was super helpful and everything went smoothly. I highly recommend them for service or a new unit.

[Golfmedik]

If the fan is in the AU mode, it will cycle more frequently than in either HI or LO and may not even come back on at all if the control board is bad. If used in the LO mode, the AC units tend to freeze up here in the south due to humidity. I was told by Dometic to always run the fan in HI here in the south.

[kozzy]

Mine does that same thing, but appears to be operation normally, I just assumed it was what the Dometic units did...
I have not had an issues with freeze up, and once I got the T Stat issues solved, both AC's have been working fine..

[Rex-]

Kozzy, Are you saying that your compressor and fan also cycled erratically as I explained ours was doing? If so it sounds like after you changed the stat the cycling went away?

[kozzy]

Sorry, it was confusing, I meant that the way the compressor cycles appears to be the norm. The issue I initially had was the upstairs unit would run, cool the upstairs to temp, and then shut down as expected. It would never turn back on thought when the temp started to rise again. My main unit operated normally.
After I replaced the TSTAT 2 times, that problem was resolved BUT I noticed, both before and after that issue, that the compressor will sometimes cycle weird. The unit would be running, I would hear the compressor shut off for like 10 seconds, while the fan stayed on, and then start running again. Both the units do it once in a while. I think its weiord, but both units seem to function fine, so I am assuming that it is just the way the units are supposed to operate. I have called dometic a few times on it, and really have no clear answer on it. When its really hot out, I make sure the fan is in HIGH mode, that way the compressor will come on and off as needed, but the fan remains running, to prevent freeze up That was recommended by Dometic. I have never had a freeze issue. Hope this helps explain it a little better .. I did have an issue with the coach not cooling well, and I simply cut some of the louvers out of the vents in the ceiling to allow more air flow and that helped immensely.