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Old 08-06-2019, 06:46 AM   #21
NotyetMHCowner
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My unit will actually short cycle (compressor restarts too quickly right after just turning off) if on AUTO. It actually burned up my compressor within the factory warranty once. I started paying more attention to it and realized what it was doing and wont use AUTO for that AC. The bedroom AC works like it should but not the living room, so I just change the fan speed to what I think it should be.

When I asked the tech about it, he said it was designed to shut off when changing fan speeds. Then it turns right back on to the new fan speed and starts the compressor right back up. I'm talking within 10 seconds or so.
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Old 08-06-2019, 08:34 AM   #22
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mine was long cycling last weekend, so i turned the duct and pointed it at my thermostat. it started short cycling so i turned it some more to get the cold direct air off it. problem solved.
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Old 08-08-2019, 07:58 AM   #23
MarknLeanna
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As a 2018 Cougar owner I can tell you we have similar problems. The Dometic thermostat does not work well - we leave the cover off all the time. Not sure how such a poor performing thermostat could make its way into an RV. Our Cougar is a 40 ft 5th wheel with 2 units - so we have twice the problem. It seems to happen anytime but as the outside temperature drops seems to be the trigger. I just lower the temp and that seems to help. I read somewhere to clean the coils and I am going to try that. Wish I could help more but will pass along any solutions that work.
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Old 08-08-2019, 10:40 AM   #24
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Quote:
Originally Posted by travelin texans View Post
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
Probably true about HVAC tech not working on RV A/C. However, they can add refrigerant, and if a good tech, add a good leak stop. These are not throwaway units like some think. I have worked on several rooftop units but with controls on the unit not with remote thermostats.
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Old 08-08-2019, 11:09 AM   #25
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Originally Posted by 6.2 Superduty View Post
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.
Sounds like you have the exact same issue. It was doing it all night last night. Sometimes it would work normally. Sometimes it would cycle the fan on once or twice and then the compressor would finally come on when it cycled on the next time.

Ha, that's a great "fix" by the dealer!
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Old 08-08-2019, 11:13 AM   #26
Al D.
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I'm following. I have a 2018 Montana High Country and the living room a/c acts up from time to time just like this. I haven't tried to resolve tho. I just put the fan on either hi or low and leave it a few hours and switch back.
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Old 08-08-2019, 01:18 PM   #27
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I also have a 2018 Montana High Country that seems to have the same issue on the main air conditioner. The tech told me not to use the auto setting, to only use the High fan setting. The bedroom A/C work correctly, but it seems to help when I run both fans on the high setting.
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Old 08-08-2019, 02:02 PM   #28
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Mine did the same thing the past two nights. I saw mention of the icing sensor in a previous post and was wondring if that might be the cause. I looked up into the system and found the sensor jammed into the fins of the cooling (evaporator?). When I pulled it out of the fins, it was wet. I thought about pulling it out and leaving it out as a test, but was worried about damaging the unit. After all, that sensor is there for a reason, right?
This might be the reason that the AC guys say to run with the fan in manual mode. That might help dry the evaporator between compressor cycles???
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Old 08-08-2019, 03:37 PM   #29
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I don't believe these units have a low pressure switch. If that is the case, the compressor cannot short cycle due to low pressure. Second, the OP stated only the fan was coming on not the compressor. Again this indicates the originally posted problem does not involve the compressor short cycling. Another commented that when the ac on his unit switched speeds that the compressor shut off as well as the fan, then the compressor and new speed selected, resumed. On My 2019 Alpine, when the a/c changes speeds, the compressor does not shut off rather only the fan speed changes after a brief pause. I've successfully restored a Dometic capacitance thermostat to operating condition, for a friend, by applying a small dab of Noalox paste to each of the sponges of the face plate. As an A/C tech, I'd suggest removing the 3 thermostat wires overnight to see if the blower comes on uncommanded. At least you'll know if the stat is the culprit.
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Old 08-08-2019, 03:54 PM   #30
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I don't believe these units have a low pressure switch. If that is the case, the compressor cannot short cycle due to low pressure. Second, the OP stated only the fan was coming on not the compressor. Again this indicates the originally posted problem does not involve the compressor short cycling. Another commented that when the ac on his unit switched speeds that the compressor shut off as well as the fan, then the compressor and new speed selected, resumed. On My 2019 Alpine, when the a/c changes speeds, the compressor does not shut off rather only the fan speed changes after a brief pause. I've successfully restored a Dometic capacitance thermostat to operating condition, for a friend, by applying a small dab of Noalox paste to each of the sponges of the face plate. As an A/C tech, I'd suggest removing the 3 thermostat wires overnight to see if the blower comes on uncommanded. At least you'll know if the stat is the culprit.
True these units have no low pressure switches. I realize short cycling is not quite the correct terminology for this issue but it's similar and the only thing I could come up with to describe it.

Obviously others are having similar issues but I don't know if it is that common. I really wonder if it has something to do with only certain configurations in certain RVs? Like I said everything on mine has been replaced except for the wires and it's still doing the same exact thing.
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Old 08-08-2019, 05:52 PM   #31
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Originally Posted by travelin texans View Post
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.l
A tech who knows his beans can add the necessary ports. I had it done to my old rig, and a recharge gave it a second life.
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Old 08-08-2019, 07:15 PM   #32
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A tech who knows his beans can add the necessary ports. I had it done to my old rig, and a recharge gave it a second life.
Labor rates being what they are I bet it’s cheaper to replace the unit.
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Old 08-08-2019, 09:13 PM   #33
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Labor rates being what they are I bet it’s cheaper to replace the unit.
It cost me $275, and it was also a heat pump unit, so I think I made out OK.
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Old 08-09-2019, 01:52 AM   #34
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Most techs will no longer install ports on AC units. The equipment and refrigerant is WAY to expensive for most people to be able to afford, and more often than not, the fittings will leak over time due to the excessive vibrations caused not just by the AC unit but the motion of the vehicle. More often that not, it is cheaper to replace the unit than it is to try and fix the old one.
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Old 08-09-2019, 05:52 AM   #35
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I also was having the same problem. I replaced the dirty air filter and it stopped cycling over and over like it was.
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Old 08-10-2019, 12:02 PM   #36
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So I am trying this new setup. I found the idea here:

http://www.klenger.net/hvac.html

It's basically using the new thermostat as a temperature switch to turn the power to the Dometic thermostat off and on at whatever you set it to.

You set up the Dometic thermostat for the fan mode you want and set it to cool and turn the temperature setpoint all the way down to minimum (55 degrees). Then you set the new thermostat to cool at the desired temperature and it controls the power to the old Dometic one. Since the Dometic thermostat remembers it's last settings once you set it up for cooling you never have to touch it.

The heat works the same way, just set the Dometic to heat at maximum (90 degrees) and then set the new thermostat to heat at the desired temperature and it will control the furnace.

Now I just have to see how it works out. Since the Dometic thermostat is always calling for cool or heat it will never be trying to cycle on the thermostat and hopefully the problem we have will be "solved".

Pros: fixes our problem cheaply <$30, it has a readout for actual temperature without having to fiddle with the thermostat.

Cons: Needs two AA batteries to power it up. A little complicated to set up and operate.
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Old 08-10-2019, 05:05 PM   #37
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This solution of adding a thermostat to cut power to the existing stat, does indeed signal the the issue all along, was the existing thermostat. I'm curious as to why the 2nd thermostat was installed rotated counterclockwise 90 degrees?
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Old 08-10-2019, 05:21 PM   #38
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This solution of adding a thermostat to cut power to the existing stat, does indeed signal the the issue all along, was the existing thermostat. I'm curious as to why the 2nd thermostat was installed rotated counterclockwise 90 degrees?
The picture is rotated sideways so it's not really like that.😁

I've tried two new thermostats and the problem still occured. I also know of at least one other person that has a very similar problem that has also replaced the thermostat with no changes. I find it hard to believe that two thermostats could be bad and causing the same exact problem.

I decided to go this way because it had a high probability of success and I actually like the older analog thermostat better. I mean who designs a thermostat that doesn't show the actual temperature unless you turn it off and push a button? That's how the new Dometic works.

Maybe we will eventually get a better product that I can install but until then I can live with this. And I won't be waking up at night listening to the fan cycle on and off wondering if the compressor is going to start or not.
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Old 08-11-2019, 10:30 AM   #39
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I mean who designs a thermostat that doesn't show the actual temperature unless you turn it off and push a button?
I bet he used to work for my microwave manufacturer. It has a clock, but won't show you what time it is unless you open the door, because somehow this will save the planet.
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Old 08-11-2019, 05:25 PM   #40
6.2 Superduty
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Originally Posted by Steveo57 View Post
So I am trying this new setup. I found the idea here:

http://www.klenger.net/hvac.html

It's basically using the new thermostat as a temperature switch to turn the power to the Dometic thermostat off and on at whatever you set it to.

You set up the Dometic thermostat for the fan mode you want and set it to cool and turn the temperature setpoint all the way down to minimum (55 degrees). Then you set the new thermostat to cool at the desired temperature and it controls the power to the old Dometic one. Since the Dometic thermostat remembers it's last settings once you set it up for cooling you never have to touch it.

The heat works the same way, just set the Dometic to heat at maximum (90 degrees) and then set the new thermostat to heat at the desired temperature and it will control the furnace.

Now I just have to see how it works out. Since the Dometic thermostat is always calling for cool or heat it will never be trying to cycle on the thermostat and hopefully the problem we have will be "solved".

Pros: fixes our problem cheaply <$30, it has a readout for actual temperature without having to fiddle with the thermostat.

Cons: Needs two AA batteries to power it up. A little complicated to set up and operate.
I hope this works but I have a question. If the dometic thermostat is set to 55 degrees and the new analog thermostat is set to the desired temperature what speed would the fan run? I will assume high.
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