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Old 07-31-2019, 05:44 AM   #1
Steveo57
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Dometic AC short cycling problem

I have a 2018 Keystone Cougar trailer with a 15k btu dometic brisk air 2 AC. It has the single zone wall mounted capacitive touch thermostat.

Frequently in the late night/early morning hours the AC fan will come on in auto and run for a minute or so and then cycle off, the compressor doesn't come on. The fan will come back on after a minute or so and then cycle off again with the compressor not coming on again. This will happen 2,3,4 times and eventually the compressor may turn on and run normal but not always. Sometimes the fan just keeps cycling on and off until I adjust the thermostat down a degree or so. It runs fine during the day.

I run the fan in auto and haven't tried running it on low or high to see what happens. The unit is not freezing up.

Either I or Dometic has replaced every component. New thermostat, control board, freeze sensor and even the AC upper unit. So basically everything has been replaced.

Has anyone else seen a problem like this? I have only seen it happen at night and it usually doesn't start until the middle of the night.
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Old 07-31-2019, 06:38 AM   #2
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Both us techs sitting here waiting to start our day think the thermostat is the culprit. That “touch”!thermostat is a huge PITA, and we are currently waiting for a bunch of new “faces” with upgraded foam.

Have you tried leaving the touch cover off and see what happens?
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Old 07-31-2019, 06:53 AM   #3
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Probably not your issue but I had similar symptoms on my unit and this was the issue. I started a thread a couple weeks back about this same issue.

Here is what I posted.

Hi all,

I thought I would share this story just in case it helps someone else. So on Friday night the wife and I go to bed and I can hear the AC cycling on and off every 5-10 minutes. It would run for 30-45 seconds and off it goes. I am lying in my bed now not sleeping thinking what the hell is going on with the AC. I lay there most of the night planning my repair attack for the morning. So at first light I wake up shut off the AC and rip the thermostat apart, no problems there appears to be working and getting good voltage. Next I get up on the side of roof very gingerly and remove the cover on the AC and I have the wife turn on the unit. Everything seems ok but the same thing it goes on for 45 seconds to a minute and shuts off and restarts 5-10 minutes later. I was just about to throw in the towel and call a mobile repair and I see the DW turning one of the other roof vents. So I ask her what she is doing and she states I want air blowing in these areas. Low and behold she had turned a roof vent close to the thermostat to point directly at it and when it cycled on it would bring the thermostat up to temp and shut off, 5 min later back on again. What a waste of 3 hours on a Saturday. I have told her she is no longer allowed to touch the roof vents.
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Old 07-31-2019, 06:57 AM   #4
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Sounds like the thermostat to me also. My guess would be that if it's not the faceplate foam issue, I'd consider it "probably the temperature anticipation circuit". My guess, if removing the faceplate doesn't confirm the "foam cushions" on the switches to be the problem (which would usually require a thermostat replacement, then it is probably the anticipation circuit, I'd replace the thermostat.
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Old 07-31-2019, 08:23 AM   #5
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I've tried it with the faceplate off and same thing happens. The thermostat is brand new. When I contacted Dometic about the faceplate issues they just sent me a whole new thermostat. I'm thinking it's still the thermostat also. Might just try a third one?

Curious why it only happens at night though?
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Old 08-02-2019, 05:58 AM   #6
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Originally Posted by Steveo57 View Post
I have a 2018 Keystone Cougar trailer with a 15k btu dometic brisk air 2 AC. It has the single zone wall mounted capacitive touch thermostat.

Frequently in the late night/early morning hours the AC fan will come on in auto and run for a minute or so and then cycle off, the compressor doesn't come on. The fan will come back on after a minute or so and then cycle off again with the compressor not coming on again. This will happen 2,3,4 times and eventually the compressor may turn on and run normal but not always. Sometimes the fan just keeps cycling on and off until I adjust the thermostat down a degree or so. It runs fine during the day.

I run the fan in auto and haven't tried running it on low or high to see what happens. The unit is not freezing up.

Either I or Dometic has replaced every component. New thermostat, control board, freeze sensor and even the AC upper unit. So basically everything has been replaced.

Has anyone else seen a problem like this? I have only seen it happen at night and it usually doesn't start until the middle of the night.
I have a 2018 Bullet with the exact problem. I haven't attempted to solve the problem.
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Old 08-02-2019, 07:56 AM   #7
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Originally Posted by Steveo57 View Post
I've tried it with the faceplate off and same thing happens. The thermostat is brand new. When I contacted Dometic about the faceplate issues they just sent me a whole new thermostat. I'm thinking it's still the thermostat also. Might just try a third one?

Curious why it only happens at night though?
We wonder the same thing. I have watched that style of thermostat just "go crazy" and cycle through what ever mode it wants and change the temp with the face off and not touching it. Can Dometic send you the 3 button as a replacement?
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Old 08-02-2019, 10:53 AM   #8
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Maybe i misread your post, is the new themostat on and you are still having the same issue?
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Old 08-02-2019, 06:12 PM   #9
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We wonder the same thing. I have watched that style of thermostat just "go crazy" and cycle through what ever mode it wants and change the temp with the face off and not touching it. Can Dometic send you the 3 button as a replacement?
I have spent a few sleepless nights playing with it. I've watched the thermostat while it's doing this and it is showing that normal display. I've tried it with the faceplate off and on and it doesn't make any difference.

Of course my discussions with Dometic have been fruitless. They tell me to reset the thermostat which I've done many times. They try to blame it on the fan doing it's normal shift from high to low when that is not even close to what it's doing.

And ultimately they say I will have to take it to a service center to have it looked at. Of course they will not be able to reproduce the problem unless they are willing to spend a few nights sleeping in the trailer in the right conditions.

I know several other people with very similar problems and they are getting nowhere with a fix. I really don't understand how you can completely replace everything and still have the same problem.

My next step is to relocate the thermostat and run a temporary wire to the AC unit to see what happens. The only thing I haven't replaced is the wire from the thermostat to the roof unit.
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Old 08-02-2019, 06:14 PM   #10
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Maybe i misread your post, is the new themostat on and you are still having the same issue?
Yes every component of the system has been replaced by me or by Dometic. New thermostat, new control board, new freeze sensor, new upper AC unit. The only thing that's original is the wires.
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Old 08-03-2019, 06:44 AM   #11
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Yes every component of the system has been replaced by me or by Dometic. New thermostat, new control board, new freeze sensor, new upper AC unit. The only thing that's original is the wires.
I am following this thread even though I have a totally different AC and thermostat. When you mentioned "everything but the wires" it reminded me of an issue I had with my AC, it turned out I needed to run a new (larger) ground wire from the thermostat. I did and it solved my problem. I first ran a temporary ground from the thermostat to see if that was the issue and it was, then I ran the ground wire through the wall.
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Old 08-03-2019, 09:16 AM   #12
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Since I have the identical problem I am going to try something this week . I suspect what may be happening is the thermostat signals the ac on but the air then circulates around the thermostat and signals it to turn off before the compressor turns on. Then it repeats the cycle until th he sun comes up and warms the camper up.
I will put a shield around the thermostat and see what happens.
Will the old style thermostat work with this unit?
Will a Airxcel thermostat work?
Starting a seven day trip Monday, I'll see what happens.
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Old 08-03-2019, 10:40 AM   #13
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Since I have the identical problem I am going to try something this week . I suspect what may be happening is the thermostat signals the ac on but the air then circulates around the thermostat and signals it to turn off before the compressor turns on. Then it repeats the cycle until th he sun comes up and warms the camper up.
I will put a shield around the thermostat and see what happens.
Will the old style thermostat work with this unit?
Will a Airxcel thermostat work?
Starting a seven day trip Monday, I'll see what happens.
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So yours is doing the same thing only at night. Let me know if you find out anything with your experiment. I have the vents turned so they're not blowing at the thermostat. The fan only runs for a minute or so though and the sensor is pretty well shielded under the cover so I would be surprised if it senses much change in that short of a period.

But I do think it has to be something to do with the thermostat location or wiring since I can replicate the problem even with all new components.

The old style analog thermostat will work I believe but you would have to replace the control board with the old style also. These newer thermostats only have three wires and send the signal to the control board on a single communication wire.
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Old 08-03-2019, 10:45 AM   #14
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I am following this thread even though I have a totally different AC and thermostat. When you mentioned "everything but the wires" it reminded me of an issue I had with my AC, it turned out I needed to run a new (larger) ground wire from the thermostat. I did and it solved my problem. I first ran a temporary ground from the thermostat to see if that was the issue and it was, then I ran the ground wire through the wall.
Interesting. I will try just running a new wire temporarily because I believe it has something to do with the wiring run or thermostat location.
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Old 08-04-2019, 04:13 AM   #15
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I put a new Brisk Air II 15k unit in my camper in 2016 and it has done the short cycle since new, not nearly as often as the op's unit but it does it several times a day. I need to check the vents.
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Old 08-04-2019, 06:28 AM   #16
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You dont have to take it to a trailer shop to have it looked at.
It's an air conditioner call an HVAC contractor. They can diagnose the problem, you might have to buy the part so they can replace it, that's the worst case scenario.
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Old 08-04-2019, 06:29 AM   #17
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Short cycling is usually the term for the compressor running for 30 seconds or so and shutting off, fan runs. This is usually caused by a lack of refrigerant.
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Old 08-04-2019, 07:04 AM   #18
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You dont have to take it to a trailer shop to have it looked at.
It's an air conditioner call an HVAC contractor. They can diagnose the problem, you might have to buy the part so they can replace it, that's the worst case scenario.
Doubt you'll find a residential HVAC tech to look at a rv, #1 they won't get on the roof, #2 if it's refrigerant issue they can't do anything, there's no ports to add coolant. If you have a friend of a friends cousin that's a HVAC guy maybe, but doubtful finding one from the yellow pages that will be of any help. Might try mobile RV technicians, better than letting sit at a dealership the rest of the summer.l
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Old 08-04-2019, 11:52 AM   #19
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Call the manufacturer and ask for a list of authorized repair people in your area
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Old 08-06-2019, 05:35 AM   #20
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So yours is doing the same thing only at night. Let me know if you find out anything with your experiment. I have the vents turned so they're not blowing at the thermostat. The fan only runs for a minute or so though and the sensor is pretty well shielded under the cover so I would be surprised if it senses much change in that short of a period.

But I do think it has to be something to do with the thermostat location or wiring since I can replicate the problem even with all new components.

The old style analog thermostat will work I believe but you would have to replace the control board with the old style also. These newer thermostats only have three wires and send the signal to the control board on a single communication wire.
Here it is day 2 of our trip and experiment didnt change anything. It is overcast this morning so fans keeps cycling without compressor running. If I turn down a degree compressor will run.
When I described problem to dealer they tell me not to use auto setting.
I would like to find someone that has this exact system that works properly.
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