2020 Dometic A/C Problems - Page 4 - Montana Owners Club

sourdough · 07-23-2020, 10:05 AM

IMO the Dometic CT thermostat is a defective design...period.

In my previous 14 I began to have issues with the AC system. Some similar to what has been described here but others as well. It would change set points, it would switch from F to C - all on its own as if it were possessed. Finally determined it had to be the thermostat so replaced it. In short order it began to act "wacky". I called Dometic and the lady said yes, they had had a bad "batch" of the CT thermostats so sent me a faceplate first, then a complete thermostat. Long story short I went through 4 thermostats and carried a spare.

The foam under the faceplate really has no bearing on the malfunction that I could determine. I trimmed them, stretched them...no help. They tell you not to depress them....just touch them...and therein lies the issue I believe. They look for "something" but whatever that is the thermostat interprets what it wants to for that "input". I did remove the faceplate and use my fingers on the metal prongs which seemed to work but is even more ridiculous. I even stood in front of one and just waved my hand back and forth in front of it and it changed values.....what! And it continues to this day. When I talked to Dometic I told her I wanted to go with a different design...no such luck. These particular ACs require that particular thermostat....

Bought this trailer in TX while in FL. Knew it had the Dometic thermostat and it was almost a showstopper but I do like the Dometic AC units and the other things the trailer offered so went ahead with it. Heck, I'm used to it now and know the drill; go to sleep, get hot, come in turn the thermostat off and let it sit a minute, turn it on and all is well. Later repeat the process. When it starts short cycling...repeat. I chalk it up to the love of the "RV experience".

432bartman · 07-23-2020, 10:22 AM

We've read all the problems with these AC units and it seems the only way around the problem is to never use the auto feature and just run hi or low.

**scottz** · 07-23-2020, 11:20 AM

Quote:

Originally Posted by bjacobs3791RD

Scottz,

The switching in auto mode from high fan to low fan happens as it approaches 5 degrees away from the set point (I think that's a little early, but that's for another day).

Last week when it shut down on me it was set on 68/High Fan. When I woke up, it was 77 degrees inside, fan running on high, compressor off. As always, went through the modes, off, back to cool and the compressor kicked right on. The fan actually never even shut down.

It seems it's frustrating for everyone except Dometic and Keystone. I'm tired of it and I know the guys at Sherrod RV are tired of getting the runaround. No telling how many hours they've wasted working on this, waiting on hold (1hr 45min when I was up there one afternoon), etc. Time they could've spent fixing other rigs, it's not like mine was the only thing they had going on.

Brandon

Sounds like multiple issues. When mine quit, they shut down completely, no fan. I have never had them do it when running the fan on high; only when on auto, once or twice when on low. And only when using both units. I am convinced the units are freezing each other up. The duct work is a continuous system allowing air from one unit to flow to the other; verify this by turning your main unit on, you will get airflow in the bedroom. If a unit is on auto, and shuts down upon reaching set point while the other unit is still running; freeze up time for the unit that shut down. High humidity makes it worse. Just my thoughts and, of course, very intermittent.

I think I helped the problem considerably when I aligned the units properly with the holes in the roof; but not a lot of use since then to verify.

Best of luck to you.

GHallof · 07-23-2020, 11:29 AM

Hey Scottz,

I too am at wits end. I just got done opening all of the ducts. Returns were all collapsed. I went ahead and opened up the flow ducts also. Noticed a difference for sure. Is it complicated to check for proper alignment of the units?

**scottz** · 07-23-2020, 12:29 PM

Quote:

Originally Posted by GHallof

Hey Scottz,

I too am at wits end. I just got done opening all of the ducts. Returns were all collapsed. I went ahead and opened up the flow ducts also. Noticed a difference for sure. Is it complicated to check for proper alignment of the units?

Check out this thread.
https://www.montanaowners.com/forums...ad.php?t=75245

Depends on you and how comfortable you are working on the the roof. It is not difficult, remove a few screws and pull the cover off, carefully remove the foam that covers the blower. At this point you can stick your hand in and feel if it is aligned properly.

If it is not aligned, remove 4 lag bolts that hold the unit to the roof. There is no sealant, just foam that seals the unit to the roof. Once loose, there is enough slack in the wiring that you can tip the unit up and check alignment. On my front one, all I had to do was reposition the foam on the bottom of the AC unit and bolt it back down. On my rear one, it was too far off, I had to move it a couple inches. I used dicor to seal the old lag bolt holes. If you go this far, get some of that aluminum tape from a home supply store and repair the lousy job the factory did sealing the duct/roof junction. Photos in the link above. When you tighten the lag bolts attaching the units to the roof, don't tighten them too much, just compress the foam for a good seal. If you tighten them too much, the bottom of the AC unit will bend to match the curved roof and the cover won't fit right; trust me on this.

Just don't fall off the roof. I had a friend do that; crippled to this day.

Good luck.

RMcNeal · 07-24-2020, 04:48 AM

I wish it was as simple as running on High or low instead of Auto. None of that seems to matter with mine. On High (or low) the fan continues to run, but the compressor never kicks on. It just keeps blowing warmer and warmer air until I turn off the thermostat and reset it. If Dometic can't or won't fix this, then I think Keystone should replace units with some other brand, maybe Coleman. The AC units cool very well when you can keep them running, and are quiet (not whisper quiet but quieter than others we have had).
Unfortunately, they are useless to us since I can't risk leaving the camper for more than an hour with our two English Bulldogs inside. If they get too hot or overheated, they'll die. Now I have a camper that we love to use, but can't leave to go anywhere for fear of killing our dogs. There's got to be a better answer than this!

bjacobs3791RD · 07-28-2020, 02:37 PM

Round and round we go...Keystone stupidity strikes again. We've been in contact with Greg at Keystone throughout the last three months. Last month when the Montana was at the shop they went through scenario after scenario, test after test that Keystone relayed to Sherrod RV from Dometic. It was determined that it was not anything to do with the units on the roof and sent another set of thermostats to install. As I stated in my last update, this worked for two weeks and the behavior returned.

Fast forward to today, Keystone has approved two new upper units because that is all Dometic will approve....the same Dometic that stated that it was not the upper units.

The service manager suggested to Greg at Keystone that we swap for Coleman Mach 15 units like the 2021's have (and the late build 2020's). That suggestion was swept off the table because they can only replace what Dometic approves..

At what point do you, as Keystone, stand behind the product YOU ultimately roll out of YOUR factory as a finished product and not pass the buck off? If you want to get picky, 90% of what is on our trailers is made by another company, big items to small. Where do they draw the line and take responsibility, have a bit of pride in the product you make? If a wire has a portion of the insulation stripped down to bare copper are they going to blame the manufacturer of the wire?

Very frustrated with Keystone's pi$$ poor customer service, it's not like I'm asking for a brand swap on my first trip to the shop. This has been ongoing for over three months in and out of the shop, time to take another route.

RMcNeal · 07-29-2020, 05:13 AM

Brandon, have they considered re-wiring the A/C units to run independently? IOW, forget about the dual zone crap and put regular thermostats in. I am still of the opinion that the problem lies in the dual zone control and thermostat system. The A/C units run fine when you can keep them running.

bjacobs3791RD · 07-29-2020, 08:56 AM

Quote:

Originally Posted by RMcNeal

Brandon, have they considered re-wiring the A/C units to run independently? IOW, forget about the dual zone crap and put regular thermostats in. I am still of the opinion that the problem lies in the dual zone control and thermostat system. The A/C units run fine when you can keep them running.

Hey Robert,

I have two independent CT Thermostats like in the picture below, one in the bedroom and one in the kitchen each controlling one unit. I know you have the Legacy package, but don't we have the same single zone thermostats?

RMcNeal · 07-29-2020, 09:21 AM

Yes, ours are the same. Back in October when this first started one of our techs suggested going to a regular non CT thermostat. At that time the only tstat that would work with these dual zone units is these CT junk. Something in the way the units work together since they share duct work. IDK. Just wondering if by now they have come up with something better since these CT style tstats have been such a problem.

RMcNeal · 07-29-2020, 09:23 AM

BTW, the new face plates they sent me are even worse. As soon as I put them on and hook up power the display goes wonky and the unit won't turn on. It keeps cycling through different modes and settings on its own while I watch.

bjacobs3791RD · 07-29-2020, 10:58 AM

Quote:

Originally Posted by RMcNeal

Yes, ours are the same. Back in October when this first started one of our techs suggested going to a regular non CT thermostat. At that time the only tstat that would work with these dual zone units is these CT junk. Something in the way the units work together since they share duct work. IDK. Just wondering if by now they have come up with something better since these CT style tstats have been such a problem.

I talked to them about changing to a different thermostat. Suggested using two multi-zone CCC thermostats, each only controlling only one unit but the wiring is completely different and won't work with the control board up top. Apparently the CT series is the only one that will work with our Blizzard units, Dometic doesn't make the three "real button" single-zone thermostats anymore.

Record a video of the thermostat cycling through modes on its own. Maybe Dometic will listen a little closer seeing the problem, although I'm not even sure Dometic or Keystone has even looked at the videos I've uploaded.

RMcNeal · 07-29-2020, 11:22 AM

Yeah, therein lies the problem. They only make the defective thermostats, so there's no way to move to something that works. The more they upgrade the plumbing, the easier it is to stop of the drain. This stuff isn't rocket science. It's an on/off switch that reacts to variations in temperature for christ's sake! It doesn't have to be that fancy.

sourdough · 07-29-2020, 12:51 PM

Quote:

Originally Posted by RMcNeal

Yeah, therein lies the problem. They only make the defective thermostats, so there's no way to move to something that works. The more they upgrade the plumbing, the easier it is to stop of the drain. This stuff isn't rocket science. It's an on/off switch that reacts to variations in temperature for christ's sake! It doesn't have to be that fancy.

I came across this possible solution on another forum (I believe). If it was posted here I apologize but did not find it;

https://www.microair.net/products/ea...24#CompatChart

I'm figure I'm going to order at least one to replace one of the CT Dometics I have in this unit to see if they work. The CT Dometic is just plain inferior IMO.

RMcNeal · 07-29-2020, 12:59 PM

Wow, that's $250 each and they only let you buy 1. Please let us know how it works out.

sourdough · 07-29-2020, 01:15 PM

I didn't notice that you could only buy 1? When I first saw them on impulse I was just going to order 2 because I had been up early that morning resetting the existing thermostat. It just let me put in a quantity of 2 for $498. I was at the checkout page and told DW what I was doing......she informed me that it wasn't $498 worth of hardship for me to get up in the middle of the night to make sure she stayed "cool"....

Now I'll give a run at just one of them when we get back.

Oldharley · 07-31-2020, 07:31 PM

what is the heat set to? could it be fighting between heat and ac?

**scottz** · 07-31-2020, 07:34 PM

Quote:

Originally Posted by Oldharley

what is the heat set to? could it be fighting between heat and ac?

No, you have to choose one or the other; no auto setting; at least on mine.

RMcNeal · 08-01-2020, 04:57 AM

Same here. In front unit, I only have A/C as a choice or furnace. On the rear unit, I have A/C, Heat Pump or Furnace. I can't have both A/C and heat on at the same time. The auto option is for the fan only, Auto , Low or High.

jimcol · 08-01-2020, 05:09 AM

Quote:

Originally Posted by sourdough

she informed me that it wasn't $498 worth of hardship for me to get up in the middle of the night to make sure she stayed "cool"....

I must admit I have been exposed to some of the smartest DW's by following this forum. You may be one of the smarter DH's for recognizing her intelligence.

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