Jump to content

Rear AC compressor turns on then off quickly


Recommended Posts

Posted (edited)

Update:  it is still short cycling on generator.  I didn't catch it happening yesterday, but this AM it has been doing it again.  I'm leaving the original post below.  Thank you all. 

 

Hey all, for a couple of years I've had an issue w my rear Dometic Duotherm AC.   Symptoms:  mainly I notice this in the mornings, but I think it happens more than that. The compressor will start and sometimes it may run 3 seconds up to 30 seconds and kick off.  Other times it'll do just fine. I discovered this weekend that it does NOT do this on generator. It only does it on 50A and it happens no matter where I'm plugged into.  I have replaced both the hard start and the run capacitors with no change. This past week I put in a Soft Start and while it does start up softer, it will still kick off like before.  I have also killed all power to the coach for minutes and reset the thermostat all with no change.  @Scotty Hutto and I feel this may be related to the Intellitec system.  I do not see any lights showing shedding when this happens and the fan will still run, only the compressor stops.  Has anyone been through this? Found a solution?  It will keep the bedroom cool so its not a huge deal, but it wakes me in the AMs and is a nagging issue to me. 

Edited by Steven P
Link to comment
Share on other sites

Welcome to the club...same problem. Moving the remote temperature sensor probe so it’s not touching anything helped mine although it occasionally still short cycles. The Tstat is 12V so you have to pull a fuse to power it down... in a black plastic container often in the bathroom or next to the circuit breaker panels.

  • Thanks 1
Link to comment
Share on other sites

I had the same issue.  The compressor is drawing the maximum amps or more to start and run.  A clamp on amp meter will measure the amps it is drawing.  I had to replace the whole unit.  Chuck B 2004 Windsor

  • Thanks 1
Link to comment
Share on other sites

Our units are not bad… it’s a temperature sensing issue, usually when there is only a slight difference in the set temperature and actual temperature. 
OP, when mine starts short cycling, I can stop mine from doing this by getting out of bed and lowering the temperature on the Tstat several degrees… now when it starts it usually keeps running and this is why messing with the remote temp sensor helps the issue.

  • Thanks 1
Link to comment
Share on other sites

Posted (edited)

My front AC (installed in 2010) started short cycling sometime back in 2017. During the summer of 2018 I tried replacing the hard start and run capacitors, no joy. I messed around with the remote sensor as my thermostat is located next to the bed, no joy. I even disconnected the remote sensor which then it defaults to the thermostat, no joy. Then later that fall it finally stopped working completely. We then used the rear AC until that quit just before leaving to travel back home to Florida. Not a pleasant trip. Once home I purchased two Dometic Penguin-II's and installed them with the new CCC-2 thermostat, no more short cycling!

They have been working great ever since and put out more cold air than the previous version of Penguin's.

Edited by Dr4Film
  • Thanks 1
Link to comment
Share on other sites

Posted (edited)

Just a guess ... Try replugging the communication cables at t-stat, inline ceiling connectors, and roof unit control board several times to clean the contacts.  Try some old style radio shack TV tuner cleaner if you have it.  If rear unit daisy chained from the front, also replug front unit connectors at the control board. However, this would not explain the generator operation.

Edited by amphi_sc
  • Thanks 1
Link to comment
Share on other sites

We are remodeling our house for the next couple of months so I'll be trying the above suggestions and keep everyone updated.  I did mess w the thermostat remote sensor some, but put it back like it was. 

20210603_193353.jpg

Link to comment
Share on other sites

i have the same problem, but the odd thing is that it seems to act up mostly when the rear TV is on.  And it's not the TV as I upgraded the size of the bedroom TV and the new one does the same thing.  I never spent the time to troubleshoot it as we are just occasional weekend campers that rarely use the TV's.  If somebody has figured this out i'll continue to follow as I would like to get it fixed...or if I find out what is causing it I will post the results.

2004 Monaco Knight

  • Thanks 1
Link to comment
Share on other sites

I was plagued with a nagging mysterious electronic problem in the coach for a very long time. The tank sensors were acting weird at times plus the Intellitec EMS display was indicating incorrect information at times also. Luckily, by coincidence I eventually tracked it down to a bad over the counter fluorescent lamp fixture sitting over the kitchen sink. Replaced the entire fixture versus just the ballast as the cover was cracked and in bad shape also. No more mysterious gremlins running around the coach.

  • Thanks 1
Link to comment
Share on other sites

Posted (edited)

Not doing it on generator is interesting.. shore power is usually lower voltage than what you get off of the genset (longer cables, shared use, crappy pedestal maintenance, etc). Maybe there is some high resistance in the mix somewhere. Measuring line voltage at the unit while it's doing it could be informative.

Edited by trailmug
Link to comment
Share on other sites

@trailmug @jacwjames

I was wrong about the generator.  It did short cycle this AM on genny.  I edited the original post earlier w an update at the beginning since that should change things up.  I've always wondered about the thermostat sensor being a culprit.  No vents blow directly on it.  I've thought about putting a heat gun near it when it's doing it bad to see what happens.   I like the idea of switching the intellitec around and seeing if the front does it. 

Link to comment
Share on other sites

Got it. Ours short cycled on two occasions.. the Intellitec load shedding device kept tripping erroneously. That circuit is shared with the washer, which only ever seems to draw about 4A, so I bridged the hot wires with an Alumiconn. The circuit might be overcommited by the nameplates, but in practice it stays under 20A and works fine. 

On the second occasion, the indoor temperature sensor wire broke, and made an intermittent connection. I noticed it mainly happened when the slide was extended, so I measured the temp sensor connector resistance while my wife moved the slide. The value jumped around, so I ran a new temp sensor wire, this time not in the slide. I don't think this one's your issue, since your fan continues to run, unless you're not using the auto fan setting.

Frost sensor issue would cause the compressor to cut out and the fan to go to high speed, so probably not that, unless you had the fan set to high already.

Dirty RJ-11 couplers in the ceiling cause some weird stuff as previously mentioned.

I'm not sure if these have a high pressure cutout switch inline with the compressor.. I don't think they do.

Link to comment
Share on other sites

I've wondered about the wire for the remote sensor, but mine is not in a slide, so no movement there.  I removed the plastic cover this am before work and pulled and spread the 2 wires apart to see if that makes a difference.  I've already heard it short cycle once since coming back from work.  I'll find my electronics cleaner and get on the roof and clean up contacts when I have a little free time.  

Link to comment
Share on other sites

Just a quick update.  Last night I pulled the 2 remote sensors (why are there 2? What do both do?) Further out of the cabinet and noted more short cycling.  So, when I went to bed I pushed them further in and noted no short cycling.  It's too early to tell if this will be the solution or not, but there's hope.  See pic.  @Scotty Hutto

20210608_064049.jpg

  • Like 1
Link to comment
Share on other sites

Steven, the one with the white end is the remote sensor. Have no idea what the second one is.

Where is this located relative to any of the output grilles on the ceiling? Is it located such that one of the grilles is blowing on it?

Link to comment
Share on other sites

Hey Richard,  I am attaching a pic.  The sensor is under the TV and next to the speaker bar.  This was happening way before the speaker was installed. I have no vents blowing on it. 

20210608_072236.jpg

Link to comment
Share on other sites

Mine is under the TV too, and I recently replaced the thermostat covers as they had degraded.  I'll try messing with those wires to see if they do anything...but on mine (as i have said before) I only get the short cycling when the TV is turned on...

Link to comment
Share on other sites

Well, maybe I spoke too soon.  While it was better this am before work,  now that I've been back it has run 2 cycles that lasted about 3 sec each and several cycles that lasted approx 2 min and keeps cutting on after only 2 to 4 minutes of rest in between.  Back to the drawing board.  

Link to comment
Share on other sites

Posted (edited)

Try lowering the temperature a couple degrees when it stay running and see if it keeps running. Mine will and this rules out it being a power/Intelitec issue.

Theres nothing wrong with the unit… the Tstat is turning it off. All 3 heat pumps are original on our 04 Dynasty that did the same on the BR unit until I messed with the remote temperature sensor. Having the sensor clear of everything and the clamp further back from the end seemed to help.

Edited by Ivylog
Link to comment
Share on other sites

Posted (edited)

I'm thinking @Ivylog is onto something.   Last night I took my infrared thermometer and pointed it at the front remote sensor and got 72 degrees.  Went to rear and got 80 degrees.  Started checking Temps around the BR and found it was consistently high there at the sensor. So I opened the cabinet behind the TV and realized I had my Dish Wally sitting right where that sensor exits (that cabinet has a false floor and the wire is under the floor).   I moved the Wally to the back of the cabinet and pulled the sensor out some and had a better night.  Today I removed the false floor and relocated (temporarily) the sensor to see how things go.   So far it's better, but it's early.  That makes a lot of sense to me.  The temp reading right under the Wally was 85 degrees.  I'm going to keep playing with different areas to find a good spot not affected by vents, windows, electronics, etc...  I'll keep yall posted. 

Edited by Steven P
Link to comment
Share on other sites

If the remote sensor is in a very hot environment (80's F) and the temperature you had selected on the thermostat for that zone is 72 F I would think the compressor would run continuously since the sensor never reaches the set temperature.

Is my logic incorrect?

Link to comment
Share on other sites

10 minutes ago, Dr4Film said:

If the remote sensor is in a very hot environment (80's F) and the temperature you had selected on the thermostat for that zone is 72 F I would think the compressor would run continuously since the sensor never reaches the set temperature.

Is my logic incorrect?

I think what is happening is a cycle of events.  The hole the sensors wire comes through allows heat to escape right on the sensor thus turning on the AC.  AC kicks on,  cools air, fan blows heat away from the sensor thus satisfying the sensor and shutting off the AC, then heat is escaping onto the sensor thus repeating itself.  When it kept kicking on every 2 to 4 minutes last night while the front ac stayed off, that got me looking more into the sensor.  I had the Wally literally over that hole/sensor.  When I moved the Wally to the back of the cabinet, that hole stayed a lot lower than 80. However, there are no vents for heat to escape that cabinet.  It's not hot in it except right at the Wally.  I may add some holes at the top of the door to allow heat out (later).

20210608_064049.jpg

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...