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Old 05-10-2009, 02:06 PM   #1
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Air conditioner compressor keeps cycling off - why?

I am very confused. The compressor in our rear air conditioner keeps turning off and on while the fan is running. I checked the interior and the filter is clean and everything looks OK. I climbed up on the roof, removed the cover and vacuumed the coils to be sure there was nothing that should cause it to overheat. The coils seemed OK, but they are definitely clean now. When the compressor is working the air output feels cool, so it would appear that it is not a freon issue.

The cycling occurs during the morning when temperatures are mild as well as in the middle of the day when it is currently about 103 degrees where we are. The rear unit does seem to be showing a heavier current draw than the front unit. Both, show voltages of 125v.

Is there anything else I can check before I take it in for repair? The unit is a Dometic 630515.

I certainly hope someone has some information on this.

Thanks in advance,
Bob
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Old 05-10-2009, 03:22 PM   #2
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I looked a your profile and I see you have a Beaver Patriot. You probably have an energy management system. You may have an incoming power problem from the utility pole. The energy managment system may be sheeding the rear AC load and then coming back on. Turn off the front AC and see if it still does it. Worth a try!
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Old 05-10-2009, 04:00 PM   #3
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Hi Bob,
Is this problem new or has the A/C worked this way for a long time? The important clue is that the fan keeps running.

When the temp is hot, the compressor may be suffering from an over temp condition and shutting down. The fan continues to run. This has happened to me, in the summer and in the desert. An A/C unit would have heat distress and the compressor shuts down. Once the temp cooled, either by the sun going down or traveling to a cooler climate, the unit returned to service and all is okay.

In the morning, the unit may have too much condensate on the coils. This has also happened to me. The compressor will shut down. The fan will continue to run. Once the condensate is gone, the unit returns to service.

If either of these turns out to be the source of the problem, I'm not sure what can be done to change the parameters the unit operates at.
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Old 05-10-2009, 08:08 PM   #4
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Thanks both of you for the input. I will test the load shedding tomorrow morning.

As for how long this condition has been going on, I really cannot say. This is the first time we have been in this heat. In the past I routinely shut off the rear air at night since it is quieter to just run the front one so I was unaware if it was cycling before. With temps now over 100, I became far more sensitive to what is going on in the coach and noticed what was going on. When I turned on the rear AC this morning after the cleaning, it was still cycling. I did the cleaning since I too believed that it was cycling due to overheating in the condensing coils.

I also need to drop all the AC loads and look at the Aladdin system loads. Right now it is reporting 14 amps max on leg 1 (which is where the front AC runs) and 20 amps on leg 2 when the rear AC compressor is running (9 amps when it is not). This may underscore the load shedding concept. I was going to test this this morning, but time ran out and other commitments kept me from doing this.

Again, thanks for the input. I really appreciate the help.

Bob
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Old 05-10-2009, 08:23 PM   #5
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You should not be shedding loads if on a 50A hook-up (and it sounds from your description that you are).

11 amps for the rear a/c sounds very reasonable.
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Old 05-11-2009, 02:47 AM   #6
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When you had the shroud off the unit, was the foam gasket seal in good condition and look like it was in the proper place?
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Old 05-11-2009, 08:52 AM   #7
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Quote:
Originally Posted by RV Wizard View Post
When you had the shroud off the unit, was the foam gasket seal in good condition and look like it was in the proper place?
Mike,
It looked like it was OK. But, now that you mention it, there was a small section that was not flush against the shroud. It looked like there was still a seal against air going around the condenser coils. But, I should probably go up there and make sure that the seal is good.
Thanks,
Bob
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Old 05-11-2009, 09:23 AM   #8
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In my particular case it looks like load shedding is not my problem. My wife kicked on the coffee pot and amps ran up to 27 on leg 2 and the compressor stayed on with no problem. In fact, it ran through the whole brew cycle and the coffee pot shut off while the compressor was still running. Moreover, while I am typing this my wife just turned on her hair dryer, amps shot up to 32 and the compressor is still running.

I am thinking it is compressor heat related since the cycling seems to happen at all outside temperatures. I noticed the problem when the temps were around 100, but this morning they are under 80 and the problem still exists. The air here in Mesa AZ is so dry, I seriously doubt we would have a condensate issue, but I guess that could apply. These Dometic units have all their electronics right in the input air stream and it makes seeing the cooling coils really difficult.

As for the cycling, when I turned on the unit this morning it took about two minutes for the compressor to start. (That is 2 minutes after the blower started. I note this because the front compressor comes right on when it starts.) The compressor ran for about 30 minutes, shut down for about 5 minutes then turned on for 5 minutes, then back off. And that seems to be the cycle.

I certainly want to thank everyone for the comments. They have been very helpful in looking at possible sources for the problem. Any additional comments are greatly appreciated.

I just wish Dometic had more information on the internet so a person could do some troubleshooting before having to take the unit in.

Thanks again to everyone,
Bob
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Old 05-11-2009, 09:47 AM   #9
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On our ducted Dometics (15K BTU main, 13.5K BTU bedroom), we keep the fans set in the "ON" position at the thermostat so that they run continuously as the continuous white noise is less distracting to us than having the fans cycle on and off. We then set the temperature for the front and rear zones at the desired setpoint, and the compressors cycle on and off as needed to hold the temperature in each zone. Perhaps I missed it, but I never read that the interior temperature was above the thermostat's applicable set point, just that the compressor(s) were cycling. That, and the staggered start-up, are a normal function of the Dometic control strategy associated with the thermostat in our rig. The compressor(s) will also cycle if icing is detected on the evaporator coil - have you noticed any signs of icing associated with the cycling you describe?

Unless the interior temperatures aren't being held at their respective zone set points, I don't note anything out of the ordinary in your description.

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Old 05-11-2009, 11:22 AM   #10
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How long does it run when on? I mean my A/C's have 3 settings for the blower/fan

HIGH/LOW/AUTO

Since the change in noise level when the fan turns on/off in AUTO mode bothers me big time, but the constant drone of the fan in HIGH I quickly tune out. I run the fan in HIGH full time. it never shuts off..

The compressor however, will shut off, when the room gets cold enough
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Old 05-12-2009, 10:36 AM   #11
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Rusty & wa8yxm,
Thanks for the info. As for the temps; outside was 103F, coach was 84F and the set point was 75F. And yes, in my confusion I did not notice that the back thermostat was set to HIGH versus AUTO. I have changed that back to AUTO. Given how dry it is here in Mesa AZ, icing would seem to be sort of a long-shot. I will check more. I guess we will just limp along with what we have and have someone look into it when we get back to our base.

I really want to thank everyone for their input. I can see that there are just a lot more options on this thing than I imagined. I read on another post that someone had to change out a temp relay, so I will probably need to get someone who has the proper test equipment to do the repair. I love the quality of folks on this forum. You all are very helpful.

Thanks again,
Bob
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Old 05-12-2009, 06:22 PM   #12
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Now I am more confused than every, but very happy with the result. Thanks to wa8yxm I checked the thermostat and noticed that the fan was set to HIGH rather than AUTO. I changed it to AUTO last night and the air conditioner has worked like a champ all day today -- no cycling. I know that should not make a difference, but right now the problem is resolved.

Thanks again to all who responded,
Bob
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Old 05-13-2009, 10:37 AM   #13
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Glad I could be of help and THANK YOU for letting me know I helped you

It is always nice to find out when you are right.. Cause you know what they say

"When you are right, nobody remembers, but when you are Wrong, nobody forgets"

SO Thank you for letting me know
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