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

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Bill/Diana

Southeastern Pennsylvania

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Posted: 01/03/22 02:02pm Link  |  Quote  |  Print  |  Notify Moderator

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 !!!

* This post was edited 05/15/22 02:48pm by Bill/Diana *


Bill & Diana

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Retired JSO

North Georgia Mountains

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Posted: 01/03/22 02:36pm Link  |  Quote  |  Print  |  Notify Moderator

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





Bill/Diana

Southeastern Pennsylvania

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Posted: 01/03/22 02:49pm Link  |  Quote  |  Print  |  Notify Moderator

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.

MFL

Midwest

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Posted: 01/03/22 04:00pm Link  |  Quote  |  Print  |  Notify Moderator

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

Southeastern Pennsylvania

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Posted: 01/03/22 04:38pm Link  |  Quote  |  Print  |  Notify Moderator

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.

2oldman

NM

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Posted: 01/04/22 09:24am Link  |  Quote  |  Print  |  Notify Moderator

"Your air conditioner may be short cycling because it is repeatedly starting up then overheating (and shutting down) due to a bad compressor, dirty filters, dirty coils, low refrigerant, or frozen coils. An overcharged system will cause liquid Freon to get into your compressor and cause it to malfunction"

dougrainer

Carrolton, Texas

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Posted: 01/04/22 10:28am Link  |  Quote  |  Print  |  Notify Moderator

2oldman wrote:

"Your air conditioner may be short cycling because it is repeatedly starting up then overheating (and shutting down) due to a bad compressor, dirty filters, dirty coils, low refrigerant, or frozen coils. An overcharged system will cause liquid Freon to get into your compressor and cause it to malfunction"


NONE of this will be responsible for his problem. ANY of these problems will not manifest itself in the few seconds the malfunction happens. Doug

Bill/Diana

Southeastern Pennsylvania

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Posted: 01/04/22 12:51pm Link  |  Quote  |  Print  |  Notify Moderator

Thanks everyone for taking the time to submit your ideas and thoughts about this AC problem. Hopefully I'll receive some more input.

Once Spring arrives I'll be sure to update this topic with the solution.

2oldman

NM

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Posted: 01/04/22 01:14pm Link  |  Quote  |  Print  |  Notify Moderator

Bill/Diana wrote:

Once Spring arrives I'll be sure to update this topic with the solution.
Good. One thing I find odd, or at least a lot different from mine, is that if my compressor starts up but its power is interrupted by anything like the generators failing to start it, it will not restart for at least 5 minutes. I guess it's resetting something.

Bill/Diana

Southeastern Pennsylvania

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Posted: 01/04/22 04:56pm Link  |  Quote  |  Print  |  Notify Moderator

2oldman wrote:

Bill/Diana wrote:

Once Spring arrives I'll be sure to update this topic with the solution.
Good. One thing I find odd, or at least a lot different from mine, is that if my compressor starts up but its power is interrupted by anything like the generators failing to start it, it will not restart for at least 5 minutes. I guess it's resetting something.


I understand what you are saying. If I lower the thermostat immediately after the compressor shuts down, there is always a delay before the compressor kicks in. This is normal.

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