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Old 06-24-2021, 09:13 AM   #61
Montana Fan
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Join Date: Oct 2019
Location: Louisville
Posts: 121
M.O.C. #25098
AC Freeze Up

Hi Scottz,

I have been plauged by AC issues for a while. My living room unit has always been an issue. Made the switch to Micro Air Units and I think they are great. FREEZE UP WAS CONSTANT

Right off the bat this season the unit started doing it more frequently. Last year I opened all my ducted work as it had collapsed. 1 1/4" PVC Pipe slipped into both sides of the duct work. Made a huge difference.

When it started this year I was puzzled a bit. So I went up on the roof, removed the unit cover and then the styrofoam plenum. Look down inside the return air duct and found two things. PVC pipe did not open the collapsed duct as far as I thought and the sliver duct tape holding/sealing the return duct to the structure of the RV roof had completely separated allowing an opening that appeared to allow the cold air supply side to bleed into the return system. So I reworked the opening to maximize the return air flow and resealed the entire cut opening with silver duct tape. Put the plenum back on and ensured the seams were well sealed but yet serviceable. Put the plastic cover back on and not a problem running on AUTO since.
Gordon & Victoria Hallof
Louisville, Ohio
2020 Ram 3500 HO Cummins Aisin 6 Spd
2017 3661RL
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Old 07-09-2021, 03:38 PM   #62
Montana Master
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Join Date: Apr 2017
Location: Colorado Rockies
Posts: 1,358
M.O.C. #19755
I received this information from MicroAir tech support. I don't think they will mind me passing it on.

Dometic single zone systems suffer from a problem when operating cooling in automatic fan. The fan turns off with the compressor by design and this leads to frost formation on the coils. Eventually the coil temperature drops below 27į and the control board goes into freeze lockout. It remains there until the coil temperature rises above 55į where it will allow cooling again. Several users have reported they always ran the fan on continuous mode while cooling for that reason.

Older revisions of the 351 thermostat did not report this freeze lockout condition but the current version does. We are contemplating adding a software function to remedy this condition to bypass the lockout and run the fan if it occurs in a future update. For now, please be aware of this possibility and the solution. This is an inherent flaw in the control board logic and we will release a future update to compensate for it. Until then, make sure you are up to date and run the fan in low or high if freezing up occurs.
Scott & Alta
2017 Montana 3160RL, Legacy, Onan 5.5Kw, Solar
2019 Ford F450 6.7 PSD
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Old 07-09-2021, 04:03 PM   #63
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Location: Jacksonville
Posts: 1,026
M.O.C. #25165
That sounds exactly like what they told me. I hope the update comes soon.
Robert & Diana McNeal
2019 Montana Legacy 3791RD 20th Anniversary Edition
2014 F350 4x4 6.7L SRW
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Old 07-09-2021, 05:47 PM   #64
Bob and Jeannette
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Join Date: Sep 2018
Location: Orlando
Posts: 258
M.O.C. #22589
My rear unit works fine but my front unit worked on powering up but not on thermostat calls to lower the temperature.

I relentlessly (lazy) used my in command remote to turn off the air conditioner and after several seconds turn it back on. And this works. Just before I was going to spend some time and money on a real solution everything started to work just fine and has continued working perfectly for 6 weeks or so.

I am sure that there is a relay in the gateway or on the control board in the Dometic Air conditioner that had oxidized contacts that are now clean enough to function from repeated start ups.

Some people had success using different thermostats and I am willing to bet that they are putting a higher power (VA) across the relay coil causing the relay to function fine. The initial power on with the in command system must also be providing more power to the relay coil. This has bad relay contacts or not enough coil power on a relay written all over it.

Itís a pain in the butt to turn it off and then on again to make it function but in my case enough usage led to it working normally now.
2020 Montana 3813ms legacy w/Paint
2017 Ram 3500 4X4 DRW Aisin Curt Q-25
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Old 07-09-2021, 06:20 PM   #65
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Join Date: Aug 2019
Location: Monument
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M.O.C. #24683
Me too

I put in the MicroAir 351 for my Dometic living room one-zone. Works far better than the Dometic, but I noticed in auto it would turn itself off and not restart, even though the set temperature had not been reached. I am currently approaching one week camping with the new thermostat. Outside temps from 85-96 this week. Running on FAN-LOW or FAN-HIGH it works, cools,and does not stop, works great. Guess Tech Support is right.
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dometic ac, thermostat

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