FIXED ???? Roof AC Starts...Stops...Then Run Fine

[Bill_Diana]

During our final trip for 2021 in October we had a few days the air conditioning was needed. The air conditioner would start and then run for about 5 seconds and shut down. Both the fan and compressor were starting as usual except shut down after about 5 seconds. Then about 10 to 15 seconds later the air conditioner fan & compressor would again start and this time would run normal until the thermostat temperature was satisficed. Cooled just fine.

The next time the thermostat called for cooling the same sequence would take place. Start...run about 5 seconds...stop for about 15 seconds...then start and run just fine.

This is a Duo-Therm by Dometic 595 series 15,000 BTU unit. Any ideas on what would cause this sort of behavior?

Thanks for taking the time to read and thanks in advance for your ideas & comments.


UPDATE TODAY MAY 15,2022

The motorhome has been in winter storage for the past few months and during that time I've been pondering how I could fix the AC issue.

Now this is going to sound crazy, but here it goes. When waking up one February morning the quartz time clock in the living room was performing properly. It would only play part of the song on the hour and then quit. I didn't know what to do, so lacking any solution I thought I would change the C cell batteries. Clock started working perfectly again.

Then it struck me. Maybe I should change the AA batteries in the motorhome thermostat for the air conditioner.

Today is our first trip for the 2022 season. As soon as we arrived at Country Acres Campground, Lancaster, PA.....I was extremely anxious to replace those old AA's with fresh AA's. When installing batteries I always mark the date on the battery with a Sharpie pen. These old AA's had a 4-2018 date.

Guess what? The air conditioner is working just fine. So, could it be possible it was only old batteries in the thermostat causing the problem? I have my fingers crossed and hoping the AC keeps working on the 10 day trip.

Again, thanks to all of your for your help & suggestions, You folks are the best !!!

[Bill_Diana]

MFL wrote:

Retired JSO wrote:
If the unit fan is set to auto and is trying to overcome a 3-5 degree temp differential between ambient and thermostat setting, the unit will stop momentarily and change fan speeds

This is a good explanation, as to first use, when differential is too great, while fan set to auto. However, after reaching/cooling to stat setting, fan and compressor should start/run, before temp climbs more than a couple of degrees.

OP...is the inside temp climbing too high, before stat is kicking in? At 20 yso, your stat may need replacement. If the unit cools the RV, like past years, it seems to be doing it's job.

You may want to monitor actual inside temps, with a known good digital thermometer. If the stat seems to be the culprit, I'd run fan continuous at high setting, until stat repaired/replaced.

Jerry

Thanks for the reply Jerry. I replaced the thermostat about 5 years ago. The AC never behaved this way before. The thermostat has a High/Low switch for the fan.

I'm in the northeast, so the motorhome is resting in storage for the winter months. I won't have the opportunity to test the AC again till the April/May timeframe. For now I'm trying to get some ideas on what and how to troubleshoot. Thanks again for sharing your knowledge.

[MFL]

Retired JSO wrote:
If the unit fan is set to auto and is trying to overcome a 3-5 degree temp differential between ambient and thermostat setting, the unit will stop momentarily and change fan speeds

This is a good explanation, as to first use, when differential is too great, while fan set to auto. However, after reaching/cooling to stat setting, fan and compressor should start/run, before temp climbs more than a couple of degrees.

OP...is the inside temp climbing too high, before stat is kicking in? At 20 yso, your stat may need replacement. If the unit cools the RV, like past years, it seems to be doing it's job.

You may want to monitor actual inside temps, with a known good digital thermometer. If the stat seems to be the culprit, I'd run fan continuous at high setting, until stat repaired/replaced.

Jerry

[Bill_Diana]

Retired JSO wrote:
If the unit fan is set to auto and is trying to overcome a 3-5 degree temp differential between ambient and thermostat setting, the unit will stop momentarily and change fan speeds

Thanks for the suggestion. Not sure I understand. We have had the motorhome for over 20 years and the AC has never behaved like this before.

[Retired_JSO]

If the unit fan is set to auto and is trying to overcome a 3-5 degree temp differential between ambient and thermostat setting, the unit will stop momentarily and change fan speeds