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Old 05-21-2020, 08:57 AM   #1
bjacobs3791RD
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2020 Dometic A/C Problems

Howdy!

My rig is currently at the dealer for issues with both Dometic 15K air conditioners. Dealer (Sherrod RV in Silsbee, TX) has been extremely great to work with as always, but Dometic and Keystone are giving the him a hard time diagnosing the problem as it is intermittant and not always able to duplicate. I figured I would reach out to the community and see if anyone has had a similar problem.

The A/C will cool down to the set temperature, turn off as expected and sometimes will not kick back on as temperature rises until I turn the thermostat off, let it sit for a few seconds and turn it back to cool. This happens when set on Cool and Auto. This doesn't happen all the time and seems to happen more at night. If I change settings to Cool and High or Low where the fan should run constantly, the fan will intermittently shut off and come on +/-10 seconds later. I've linked a couple videos of what is happening.

Ready to get this fixed so we can bring it to the beach for the summer!

Thanks in advance!

-Brandon

https://youtu.be/y0Wu-PSsGrM

https://youtu.be/_3D8Mh72ItQ
 
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Old 05-21-2020, 05:50 PM   #2
mlh
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I would suspect a bad connection or thermostat.
Lynwood
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Old 05-25-2020, 10:43 AM   #3
bjacobs3791RD
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UPDATE: The dealer replaced both upper control boards and both thermostats per Dometic's instruction. I picked up the rig on Saturday and had problems Saturday night and more problems this morning. Video 1 of 2 is showing the fan switching from high to low back and forth every minute while the compressor never shuts off. The setting is on “Auto / Cool” and set to 68. Video Update 2 of 2 is showing the same issue as before with the unit not turning back on as the temp rises after reaching the set point.

Video 1 of 2 https://youtu.be/EEDZ4_Xn5V8

Dark video, here are the timestamps is you want to skip through.
Start - High
0:34 - Off
0:40 - Low
1:38 - Off
1:42 - Low
2:41 - Off
2:44 - High
3:44 - Off
3:48 - Low

Video 2 of 2 https://youtu.be/rjozSWQtGns

Same crap as before. Really frustrated, I'm paying for a monthly spot at the beach so we don't lose it for the summer and can't even bring the Montana down there.
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Old 05-25-2020, 11:11 AM   #4
Desert Rat
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Just curious, this problem didn't happen during your PDI?
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Old 05-25-2020, 11:29 AM   #5
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Originally Posted by Desert Rat View Post
Just curious, this problem didn't happen during your PDI?
No, it didn’t. I bought the Montana in late September and didn’t need the A/C much. First time it did this to me was about a month and a half ago.
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Old 05-25-2020, 12:49 PM   #6
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Could the units be either freezing up or the freeze sensors are faulty?
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Old 05-25-2020, 01:22 PM   #7
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If you run ac with fan on high does it still do it? some times one will try to freeze a little but if you run the fan on high it never kicks off and will keep 'it from freezing and solve lots of problems.
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Old 05-25-2020, 03:39 PM   #8
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Originally Posted by scuba dude View Post
If you run ac with fan on high does it still do it? some times one will try to freeze a little but if you run the fan on high it never kicks off and will keep 'it from freezing and solve lots of problems.
I’ve tried it with the fan on the fan on high and low as well. It will stop blowing for +/- 10 seconds intermittently.
I don’t believe it’s an issue with it freezing up being this can happen in the first few minutes of running. Not sure about the freeze sensor being the issue either..if it was that sensor, wouldn't it not come right back on? Cycling through modes, leaving it off for a few seconds always kicks it right back on.
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Old 05-26-2020, 05:22 AM   #9
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I have been having the same issue with our 3791RD as well. I removed the faceplates from both thermostats and then reset the units and I thought that fixed it. They worked for a while like they were supposed to, then started the same problem again. I believe it is a problem with the control board(s), but I cannot remember where I read that. Please let us know when/if you find the fix.
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Old 05-26-2020, 01:27 PM   #10
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Originally Posted by RMcNeal View Post
I have been having the same issue with our 3791RD as well. I removed the faceplates from both thermostats and then reset the units and I thought that fixed it. They worked for a while like they were supposed to, then started the same problem again. I believe it is a problem with the control board(s), but I cannot remember where I read that. Please let us know when/if you find the fix.
Spent two hours with the dealer this morning when I brought the Monty back to them. Service manager, tech, and I sat in there on the phone with Dometic running through all the BS recommendations they were throwing out and we're still stumped. The freeze sensors were replaced last week when the new control boards and new thermostats were put on. One recommendation from them was the wiring between the thermostat and the unit up top. The wires that connect everything are solid core and not stranded for some damn reason, these rigs are moving and flexing going down the road. They suggested that there might be a break or a bad spot, but if that was the case it's highly unlikely that both units would be doing the same thing, and when it does act up, turning it off then back on fixes is every time.

We're still scratching our head on this..

Robert- Out of curiosity, where was yours when it acted up? Were you plugged into 50amp?
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Old 05-26-2020, 01:49 PM   #11
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We were at a private campground in Georgia when we first noticed it. Hooked up on 50 amp service. Progressive EMS says power, ground and wiring all good. It seems once it resets that it runs fine for about 8-12 hours, then it will shut off and not turn back on no matter how hot it gets. As you said, turn it off, then back on, or reset by removing face plate fixed it every time, but only temporarily.
It's a real concern for us since we have 2 English Bulldogs and can't leave them in the rig without being very close by. They can't take the heat down here. I have a camera/thermometer that will alert my cell phone if the temp gets too hot, but I better be close when it does.
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Old 05-26-2020, 01:55 PM   #12
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I agree about the wiring. One other thing I just thought of...Our first inclination that something was wrong was actually the opposite of what it is now. No matter how cold it got, the unit wouldn't turn off. It would freeze us out at night, but during the day it would shut down and not come back on. When I first noticed it, I had the AC set on 70 on both units and went to bed. Woke up during the night and my thermometer said is it was 62 and the AC was running full bore. Change the temp setting and it didn't matter. Wouldn't turn off unless I put it to off and waited. It would eventually turn off. Now its the opposite. It will turn off and not turn back on. Very strange.
I had thought it had something to do with how the units were working together. It seems the AC in the living room would stop, then immediately start back up with the fan sounding like it is on low. The bedroom AC would run on high. After a few minutes, each would shut off, then back on and the living room would be on high and the bedroom on low. This was happening all day long. The only turned off for a few seconds.
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Old 05-26-2020, 01:59 PM   #13
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I have to say it's disappointing that replacing the thermostats didn't fix it. I read in another thread that dometic sent out new thermostats for someone else and that fixed their problem. I was hoping to call them next week about it. We have another trip scheduled for the 6th for 2 weeks. I'll have another chance to "play" with it then and see what I can figure out.
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Old 05-26-2020, 02:54 PM   #14
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We are having similar if not the same issues as well on our 2020 3931FB. One thing I do know is ours will not run on high or low like our 2018 did. In other words our 2018 would run on high or low continuously and the compressor would cycle. I need to play with mine again to determine what its actually doing.
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Old 05-26-2020, 04:08 PM   #15
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Quote:
Originally Posted by RMcNeal View Post
It seems the AC in the living room would stop, then immediately start back up with the fan sounding like it is on low. The bedroom AC would run on high. After a few minutes, each would shut off, then back on and the living room would be on high and the bedroom on low. This was happening all day long. The only turned off for a few seconds.
Was it something like this? https://youtu.be/EEDZ4_Xn5V8 Saturday after I picked it up from the shop it kept flipping from high fan to low fan every minute shutting off for about 4-5 seconds between switching. (compressor remained running) AC was on 68/Auto/Cool temp inside was 70. I've read where "Auto" will run the fan on high and switch to low as the temperature inside approaches the set point (within 5 degrees). I initially thought it just may have been right at the threshold but I was well within the 5-degree range. Dark video, it was at 11:45 at night but the timestamps are there. Click on my name or YouTube account, there are 6 videos of the issues I'm having.

It's just odd to me that both units are having the "shut off and not come back on problem" even after new thermostats, new control boards, and new freeze sensors. Certainly frustrating, we are paying for our summer spot right now at the beach so we don't lose it but can't even use it..

I'm also getting information that the two AC units are not linked together as I initially thought.
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Old 05-26-2020, 04:13 PM   #16
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Originally Posted by mbjam359 View Post
We are having similar if not the same issues as well on our 2020 3931FB. One thing I do know is ours will not run on high or low like our 2018 did. In other words our 2018 would run on high or low continuously and the compressor would cycle. I need to play with mine again to determine what its actually doing.
Mbjam-- Are you saying the fan will stop even when it is set on high or low when it should run constantly? Does it come back on on its own?

Before mine went to the shop the first time I had that problem. On high or low it would shut off for +/- 10 seconds and come back on. It would do this intermittently but repeatedly.
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Old 05-26-2020, 04:32 PM   #17
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Yes that is what I am saying.

I have ours running on high as we speak. Trying to figure out exactly what its doing.
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Old 05-26-2020, 06:19 PM   #18
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Yes that is what I am saying.

I have ours running on high as we speak. Trying to figure out exactly what its doing.
Let me know if you narrow it down. Would you mind sharing what you have the temp set to and what kind of outside temp you’re dealing with?

Trying to see if I can nail down a pattern or any consistencies.

Thanks!
B
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Old 05-26-2020, 07:01 PM   #19
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i suspect it is a connection problem....the wires from the front a/c and then to the back a/c

but, at this point you can try to push for a replacement a/c and see how that goes.
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Old 05-26-2020, 08:21 PM   #20
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Set thermostat at 68. Outside is 75. Both units on high cool. Right now seems to be working fine. Going to leave on tonight and check in the am. I am in Dayton TX west of you.
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