2020 Dometic A/C Problems - Page 5 - Montana Owners Club

allenclme · 08-01-2020, 08:32 AM

Quote:

Originally Posted by RMcNeal

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.

Same here. The only thing I notice with mine now that we've changed the faceplates is the random flckering and switching has stopped. In auto mode, the rear heat pump unit will stop cooling and just run the fan when it should be calling for the compressor in heat or cool mode. If I set them to either low or high, I don't have problems.

I wanted to change out my thermostats to an old-fashioned non-touch screen but my dealer told me the thermostats are paired to the control board on the AC units and it wouldn't work.

Fisher · 08-14-2020, 12:52 PM

We have the same issue on our 2019 3721 RL. Intermittent, but only on the LR unit. We have replaced the thermostat but that did not make any difference. Following this thread to see what you guys come up with. It is frustrating for sure.

richeyb · 08-24-2020, 06:48 PM

I have to say this is a very disappointing thread to read. I was thinking I had an electrical problem keeping my AC running, but I guess I’m in the same boat. If anyone comes up with a fix please post!

Mopar_Mudder · 07-05-2021, 08:06 AM

Well this is interesting. We just got our new to us 2017 3790rd last week and took it on its first outing the day after we got it. First this I noticed with the AC is that the living room unit will not cool the living room down to 74 degrees, just runs steady never turning off. Out side temps were in the high 80's, I was expecting a much better cooling experience from this this. Now because of the lack of power at our unit, only a 20amp, I could never run both units at the same time, just one or the other.

The bedroom unit we would run at night and multiple times at night it would get blazing hot in the bedroom, never got up to try and mess with anything but then all the sudden the A/C would kick in and cool it off. Also noticed in the bedroom that the A/C would kick the fan on for a few seconds then turn back off. Other times it would cycle the fan on and off a couple of times before the compressor would kick in.

I did experience the have to turn the thermostat on and off on both units a couple of times but didn't thin much of it, just thought it was something I was doing wrong.

So I can confirm same issue in 2017 with a Legacy model. But the A/C is not controlled by the In-Command in that year that I know of. Over all happy with the unit but not with the A/C system. Has this problem ever showed up with heating? If it is the thermostat seems it should effect that also.

RMcNeal · 07-06-2021, 04:22 AM

I have never had an issue with heating, either furnace or heat pump. It runs as expected. I replaced my thermostats with the Micro Air 351. I'm still having an issue with the rear AC freezing up, but I have a plan to fix that on my next outing. The new thermostat reads "Freeze Lock Out" on it. According to Micro Air, they are working on a software update to work around that issue. Great folks there. I need to pull the cover on my rear AC and check the positioning and tape the plenum. Also, I plan to fix the collapsed duct work and re-tape the returns and vents. Until then, I've been running with the fan on high during the day and it prevents the freeze up. That didn't work with the Dometic CT thermostat. It would freeze and the compressor would never come back on. Just the fan would run.

Mopar_Mudder · 07-06-2021, 07:26 AM

Quote:

Originally Posted by RMcNeal

I have never had an issue with heating, either furnace or heat pump. It runs as expected. I replaced my thermostats with the Micro Air 351. I'm still having an issue with the rear AC freezing up, but I have a plan to fix that on my next outing. The new thermostat reads "Freeze Lock Out" on it. According to Micro Air, they are working on a software update to work around that issue. Great folks there. I need to pull the cover on my rear AC and check the positioning and tape the plenum. Also, I plan to fix the collapsed duct work and re-tape the returns and vents. Until then, I've been running with the fan on high during the day and it prevents the freeze up. That didn't work with the Dometic CT thermostat. It would freeze and the compressor would never come back on. Just the fan would run.

I would love to replace the thermostats if that is possible. Have read conflicting information on if you can or not. How stupid is it that you have to turn the Tstat off in order to see what the temp in the room is, can't beilieve they would design it that way.

I opened up the collapse return ducts last night and cut down the flange on the supply grills to increase some flow. One thing I did noticed is that removing the supply grills really seams to increase the flow of air because it can blow straight down, I might look for different grills that are more open and allow the air to blow straight down.

Had the Tstats set at 72 and they ran for probably 3 hours and it was nice and cool in their. Front A/C got down to the 72 and shut off, rear never shut off but it had to be close to 72. Called it a night and shut down the rear A/C Tstat so I could see the actual temp

and it said 81 degrees, well I know it was well below that. Then I remember I think I read somewhere that heat from the breaker panel comes up inside the wall and gives the Tstat a false reading, so have to check that next.

TheKothes · 07-06-2021, 08:03 AM

Since the time I posted on this thread I have made a few changes to improve my A/C. I replaced the thermostats with the Micro-Air brand as suggested by another thread and they work better than the stock ones. I still leave it on fan low to cut down on the cycling. It is far better than the Dometic ones. The other thing I did was added some more vents in the ceiling to allow more air to come out. It still is not enough to bring it down to 74 when it is almost 90 outside. It just does not generate enough BTUs to cool it off. It appears the third A/C and a dedicated circuit to the pedestal is the only real solution to keeping the rig cool in the extreme heat.

triplebvalp · 07-06-2021, 10:43 AM

Quote:

Originally Posted by Mopar_Mudder

I would love to replace the thermostats if that is possible. Have read conflicting information on if you can or not. How stupid is it that you have to turn the Tstat off in order to see what the temp in the room is, can't beilieve they would design it that way.

Easy-Peazy:

https://www.microair.net/products/ea...32199143555156

Mopar_Mudder · 07-06-2021, 10:48 AM

Quote:

Originally Posted by triplebvalp

Easy-Peazy:

https://www.microair.net/products/ea...32199143555156

Thanks for the link. They are a little pricy though

triplebvalp · 07-06-2021, 12:33 PM

Quote:

Originally Posted by Mopar_Mudder

Thanks for the link. They are a little pricy though

Actually, a LOT of PRICEY !!!

But, they are much more user friendly than the Dometic t-stat.

Mopar_Mudder · 07-06-2021, 12:35 PM

Quote:

Originally Posted by triplebvalp

Actually, a LOT of PRICEY !!!

But, they are much more user friendly than the Dometic t-stat.

Wouldn't be so bad if you didn't have to buy two of them, but I will probably bite the bullet and do it.

GHallof · 07-06-2021, 02:32 PM

I bit the bullet and bought two. Haven't looked back. They are well worth it!!! The company is excellent to work with. My 2017 3661RL was full of AC issues. I have done a LOT of work to get things to where it is dang near perfect. Here are the main ones that I feel made the most difference. The T-Stats brought it all together.

1. Opened up all duct work....all of it. Allowing the units to get as much air from the return lines as they can and to be able to push as much cold air out of the supply lines is key. BREATHE BABY BREATHE!!!

2. Get up on the roof and check the cut openings beneath the units, first for proper alignment and second to make sure all of the duct work is still sealed up the way it should be.

3. Insulate the cavities behind you T-Stats. I would not suggest using foam. Use the pink stuff. Find a way to tack into place so it doesn't slide down the cavity. If you use the foam and later decide to snake some wire down one of those cavities its a bit of a mess and a PITA to remove.

4. Mount your Micro Air T-Stats....and enjoy the cool breeze

triplebvalp · 07-06-2021, 06:47 PM

Quote:

Originally Posted by Mopar_Mudder

Wouldn't be so bad if you didn't have to buy two of them, but I will probably bite the bullet and do it.

You don't have to buy 2 of them, I didn't. My bedroom Dometic t-stat seems to work well so I only replaced the living room t-stat.

Mopar_Mudder · 07-06-2021, 07:44 PM

Working on the camper tonight and found a couple other things. First verified the thermostat reads atleast 5 deg cooler when you take it of the wall.

The grills in the stairs i didn't realize open right into the basement. Their has to be a ton of hot air come though them when it is hot out side, especially when some one leaves the basement door open. I know they are suppose to be return for the furnace but has to be plenty of other leaks it can pull from.

The cabinets under the living room recliners. If you look up at the ceiling of that cabinet the floor joint leave a bunch of opening that go direct to the rear storage compartment. Another source for heat to come in, not to mention smell if you put something nasty in the storage area.

triplebvalp · 07-06-2021, 08:23 PM

Quote:

Originally Posted by Mopar_Mudder

Working on the camper tonight and found a couple other things. First verified the thermostat reads atleast 5 deg cooler when you take it of the wall.

The grills in the stairs i didn't realize open right into the basement. Their has to be a ton of hot air come though them when it is hot out side, especially when some one leaves the basement door open. I know they are suppose to be return for the furnace but has to be plenty of other leaks it can pull from.

The cabinets under the living room recliners. If you look up at the ceiling of that cabinet the floor joint leave a bunch of opening that go direct to the rear storage compartment. Another source for heat to come in, not to mention smell if you put something nasty in the storage area.

Yep, there is all sorts of openings that will loose cold/hot air out of the FW. The stairs being a major source ... block those stair vents in the summer.

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