A/C Question??? - Montana Owners Club

Wisconsin Retiree · 08-09-2021, 11:44 AM

I have a Dometic 15,000 BTU A/C with heat pump in main living area of my 2019 3121 RL. The unit cools great when running but I believe I have a couple issues that may or may not be related?

First , I noticed that when unit runs and brings room to temperature right before it is going to automatically turn off because it is at thermostat set temp it will short cycle twice before stopping. In other words it will turn off for a few seconds, turn on a few seconds then off , then on & off until temperature calls for it to lick back on. It will do this every time.

Second, then after running for in excess of 14 hrs the unit will not turn on to cool again unless I turn off at the thermostat wait a few seconds and restart then good again for about the same period.

I regularly clean all air filters and ports, checked for loose connections up/down in thermostat and all appear satisfactory. Cool air coming out is at 52 degrees, all drains are flowing great & I do not see any ice up on coils when it short cycles and turns off.

Any ideas what else to look for? I am stumped?

**DQDick** · 08-09-2021, 05:05 PM

I guess the first question is, has it always done this or has it just started? Also, when it's running and short cycles twice before shutting off, what do you have the fan set on?

Wisconsin Retiree · 08-09-2021, 05:10 PM

So fan is set to Auto and I believe it did not cycle like this before? It seems very noticeable to me now and I never recall it doing this a couple months ago???

Skw774 · 08-09-2021, 05:42 PM

I run my fan on high and set the temp to 72. Does away with the short cycles

Daryles · 08-09-2021, 06:55 PM

Mine does the same. Has done this for two and a half years. If the short cycling bothers you turn the temperature down a couple more degrees.
I know some have upgraded the thermostat to MicroAir thermostats. Very expensive but very good.
https://www.montanaowners.com/forums...ad.php?t=82210

Wisconsin Retiree · 08-09-2021, 07:31 PM

Ok, I will give both a try. I am a little happier others have the same cycling issue with no serious problem yet. So I will see how it plays out. Thank you all for the input.

RMcNeal · 08-10-2021, 04:24 AM

What you describe as "short cycling" and the off and not turn on without resetting sounds just like my issues with the Dometic CT thermostats. I ended up replacing them with the Micro Air thermostats after chasing gremlins for over a year. Haven't had a problem since.
My theory on the not turning on was that the system would go into freeze lockout, even when it wasn't. The short cycling I was told was normal according to Dometic. It would cycle from High to Low when the temp nears the set point.

JDDilly · 08-10-2021, 05:29 AM

Quote:

Originally Posted by RMcNeal

What you describe as "short cycling" and the off and not turn on without resetting sounds just like my issues with the Dometic CT thermostats. I ended up replacing them with the Micro Air thermostats after chasing gremlins for over a year. Haven't had a problem since.
My theory on the not turning on was that the system would go into freeze lockout, even when it wasn't. The short cycling I was told was normal according to Dometic. It would cycle from High to Low when the temp nears the set point.

Ours was acting the same way until I installed the MicroAir. Now no issues. When the fan is in Auto mode, it does go from High to Low when the room temp gets within 3 degrees, from what I have observed, of the desired temp. I also like the bluetooth, it is nice to adjust from outside or when in the bedroom. The resort we are at in the summer is upgrading and expanding the network. I am excited to try the WiFi connectivity. It will be nice to turn on the system as we are driving there. We normally go to our camper for 2 weeks and then go home for 4 to 7 days.

Wisconsin Retiree · 08-10-2021, 05:55 AM

I am for sure willing to swap out my thermostat I will look into the Microair thermostat. Thank you.

Route66Rambler · 08-10-2021, 09:10 AM

We put in the MicroAir thermostat and it still does the short cycling. It's just how it works. Either thermostat is fine. We only changed the downstairs thermostat. The one the upstairs bedroom is the OEM.
The MicroAir is nice because you can change the temp if you are away or don't want to get up to change the temp.

Wisconsin Retiree · 08-10-2021, 09:42 AM

Got it. Appreciate that

Gary in Texas · 08-15-2021, 01:15 PM

Quote:

Originally Posted by Route66Rambler

We put in the MicroAir thermostat and it still does the short cycling. It's just how it works. Either thermostat is fine. We only changed the downstairs thermostat. The one the upstairs bedroom is the OEM.
The MicroAir is nice because you can change the temp if you are away or don't want to get up to change the temp.

I also installed the Micro Air thermostats. When I set our bedroom thermostat at night on 70, we wake up during the night with the unit off and the temp at 76. I have to turn the thermostat off then back on to get the unit to come on. Anyone else have that issue? Solutions?

cghsatx · 08-15-2021, 01:23 PM

Quote:

Originally Posted by Wisconsin Retiree

I have a Dometic 15,000 BTU A/C with heat pump in main living area of my 2019 3121 RL. The unit cools great when running but I believe I have a couple issues that may or may not be related?

First , I noticed that when unit runs and brings room to temperature right before it is going to automatically turn off because it is at thermostat set temp it will short cycle twice before stopping. In other words it will turn off for a few seconds, turn on a few seconds then off , then on & off until temperature calls for it to lick back on. It will do this every time.

Second, then after running for in excess of 14 hrs the unit will not turn on to cool again unless I turn off at the thermostat wait a few seconds and restart then good again for about the same period.

I regularly clean all air filters and ports, checked for loose connections up/down in thermostat and all appear satisfactory. Cool air coming out is at 52 degrees, all drains are flowing great & I do not see any ice up on coils when it short cycles and turns off.

Any ideas what else to look for? I am stumped?

You have the same problems most of the rest of have had with these ACs, Keystone and that era of unit (mine is 3731). You can try another set of Dometic thermostats (didn't work for me), try the Easy Touch thermostat upgrade (works better/longer but still cuts off, short cycles or stops cooling), try inserting PVC in the ductwork to improve airflow, ( seems to help), take back to dealer to fix if in warranty (waste of time) or pay 3rd party to try to fix. Personally, based on the AC issues and all the other things, I have given up and will never buy another Keystone or any thing with a Dometic AC. I am tolerating what I have now and waiting for the RV madness to cool down and will be buying something different. If you find a real fix, please post.

Byron B · 08-15-2021, 01:32 PM

We have a 2019 Montana as well. With the Legacy package. With our Dometic t-stats, I realized that when the short cycles occur, the fan had been running at high speed. The two short cycles are the other two fan speeds as it decelerates.
Our Dometic t-stats are garbage. The one in our living area will intermittently not turn on. It will flash an E1 error code and not start. I have to turn the unit off and then on again before it will work…. Sometimes neither unit will turn on in AC mode. No matter the temp or fan setting. Turn it off then on for it to work again. Pretty sad for the $$$ we pay for these rigs. Getting worse all the time.

cghsatx · 08-15-2021, 01:43 PM

Quote:

Originally Posted by gtully@tullyco.com

I also installed the Micro Air thermostats. When I set our bedroom thermostat at night on 70, we wake up during the night with the unit off and the temp at 76. I have to turn the thermostat off then back on to get the unit to come on. Anyone else have that issue? Solutions?

Mine does the same thing but I run the living area unit at night because the bedroom unit causes a vibration in the adjoining bathroom wall, which when quiet at night, I hear it. It can be felt in the thin, curved part of the wall. My first 5th wheel was a Jayco and it never had these kinds of annoying issues, except for a sorry mattress.

Bob and Jeannette · 08-15-2021, 01:43 PM

I had both issues and the short cycle at the end is normal, the front unit only working on power on I fixed. I say fixed but really all that I did was power down and power up again any time that I wanted the air to come on, after a couple of months it was no longer necessary. I did this because I am lazy and delayed climbing on the roof. This is the behavior of a dirty contact on a relay or an underpowered coil on a relay in the air Conditioning electronics. Dirty oxidized contacts on a low voltage relay are common. Low power to the coil is an engineering flaw. My guess is that we have a little bit of both. The good news is that mine and my neighbors work now after cycling the power on cycle around 100 times through normal operation over 2, maybe 3, months, less for my neighbor who cycled the power every 15 minutes for 3 days to make his work correctly.

Wisconsin Retiree · 08-15-2021, 01:55 PM

Interesting, good to know. Thank you

Gary in Texas · 08-15-2021, 01:56 PM

Quote:

Originally Posted by Bob and Jeannette

I had both issues and the short cycle at the end is normal, the front unit only working on power on I fixed. I say fixed but really all that I did was power down and power up again any time that I wanted the air to come on, after a couple of months it was no longer necessary. I did this because I am lazy and delayed climbing on the roof. This is the behavior of a dirty contact on a relay or an underpowered coil on a relay in the air Conditioning electronics. Dirty oxidized contacts on a low voltage relay are common. Low power to the coil is an engineering flaw. My guess is that we have a little bit of both. The good news is that mine and my neighbors work now after cycling the power on cycle around 100 times through normal operation over 2, maybe 3, months, less for my neighbor who cycled the power every 15 minutes for 3 days to make his work correctly.

So cycling the power cleans the contacts over time? Sorry if that’s a stupid question but thats way above my pay grade.

MSand · 06-16-2022, 07:39 AM

So, reading this thread, it sounds exactly like what we are seeing on our new 5th wheel. I was out of town, and the AC kept shutting off and not coming back on for my wife. She got it to restart the first time by tripping the breaker at the post. The second time, it did not seem to resolve the issue. The dealership asked if it was freezing up, which would most likely be a low refrigerant charge. If it is related to the thermostat, that shouldn't be too bad to change. Is there an easy way to cycle the power to the thermostat that I am missing? I tried to cycle the AC breaker in the trailer, but that did not reset it.

RMcNeal · 06-16-2022, 08:01 AM

If you have the Dometic capacitive touch thermostats, I think it was up arrow an mode. Hold until display reads -- double dash to reset.

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