A\C compressor turning off and on during certain hours only (pattern)

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vagabonds_moon

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Oct 2, 2010
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31
Hello--

My rooftop a\c unit , the compressor is cycling off and on at random points during the day - but only at certain hours: from about 6:45 pm, when my camper is covered in shade, the a\c runs normally until about 12:30 the next afternoon, when it starts to shut off and on again. The fan will continue to blow air, but it's not cool - i'll hear the compressor come back on, and it'll start to blow cold.

About 2 weeks ago, I replaced the a\c motor - for 1 week, it worked properly, then it began doing as described above. *Note that, last summer, in this exact same place, the a\c did not display this behavior.

A couple weeks ago, when I was up on roof doing the replacement, while I was wiring up the motor, gnats were swarming around me, so I hurried with the work and got off the roof. I did wrap each pair of wires with electrical tape and I thought I had the wire caps on pretty tightly.

Anyone have any thoughts as to what may be causing this behavior? I find it strange that it works normally from 6:30 pm or so until the next afternoon, but it's getting up into the 90s everyday, so i've gotta fix it.

Could it be the sun heat itself, affecting the electronics somehow? I have noticed in the past that breakers seem to trip more easily during the hottest part of the day.

I did also spray the coils with coil cleaner

I wonder if I should go back and rewire the motor again, and\or, cover the a\c shroud with some sort of reflective material, in an attempt to deflect some heat.

Thoughts are appreciated!

Edit:  Inside my camper, the square area on the ceiling where the filter is, this area will drip water when the a\c is working (I recently learned i'll need to get on roof and clean the small drain line)
During the day when the a\c works randomly, this dripping will not occur, but in evening when the a\c stays on and runs normally, the dripping comes on full force. I don't know if this is somehow related to the compressor problem, but thought I'd go ahead and mention it.
 
Just a guess, but it may be freezing up, possibly due to low refrigerant when the outside temps call for more A/C. This can overheat the unit causing the thermal protector to open up, shutting down the unit. Then as it cools down, it kicks back on.
 
Molaker said:
Just a guess, but it may be freezing up, possibly due to low refrigerant when the outside temps call for more A/C. This can overheat the unit causing the thermal protector to open up, shutting down the unit. Then as it cools down, it kicks back on.
Click to expand...

Thanks for the input- can this occur in the instance that the fan continues to run normally, just not the compressor?
If so, I'll have to learn to to check if the unit is low on freon, and how to fill it
 
vagabonds_moon said:
Thanks for the input- can this occur in the instance that the fan continues to run normally, just not the compressor?
If so, I'll have to learn to to check if the unit is low on freon, and how to fill it
Click to expand...
Yes, I believe the compressor has it's own thermal protection and the fan would continue to run if the compressor kicked off. As for how to check the Freon, you are pretty much out of luck there. These units are not made for easy service that way. It has no 'fill' port so if one wanted to service the unit, it would first have to be drained of Freon and a fill valve installed then recharged. About the best you can do short of replacing the unit is to call a servicer who is will to work on it.
 
The unit is most likely sealed with no service ports. Usually the units are replaced. I say usually because I have known a few that people had service ports added but they done there own HVAC. It is not cost effective to have someone else do it. During the time it is kicking on and off try running the fan on high and leave it on. See if this helps. Also you said you sprayed cleaner on the coils hose it down good and make sure they are clean.
 
Since you recently worked on the unit I?d have another look to be sure everything is tight and well connected
 
I am wondering if moving my rv to a place where there is shade from the sun might help, what do you folks think? Maybe that would make the difference in it overheating or not?

Meanwhile until I can move it, is there anything I could use to cover the a\c shroud with, to try and deflect some sun heat?

thanks
 
Freezing is one option. another is overheating.. IF the condernser is clogged up wioth dead nats.. Then as it gets hotter and hotter out the compressor draws more and more power. On my RV this results in the click of a 20 amp circuit breaker (Unit is supposed to draw 13.5 but will exceed 20 if overheated)  Another breaker is the Thermal breaker inside the compressor..  The difference is that one is self-resetting.

Just a thought.  By all means investigate all other options suggested.
 
I'm just curious as to why you replaced the fan motor.
Is this a new RV or new to you RV? It may help with other questions in the future if you go into your profile and create a signature of yourself telling us a little bit about you.
 
vagabonds_moon said:
Hello--

My rooftop a\c unit , the compressor is cycling off and on at random points during the day - but only at certain hours: from about 6:45 pm, when my camper is covered in shade, the a\c runs normally until about 12:30 the next afternoon, when it starts to shut off and on again. The fan will continue to blow air, but it's not cool - i'll hear the compressor come back on, and it'll start to blow cold.

About 2 weeks ago, I replaced the a\c motor - for 1 week, it worked properly, then it began doing as described above. *Note that, last summer, in this exact same place, the a\c did not display this behavior.

A couple weeks ago, when I was up on roof doing the replacement, while I was wiring up the motor, gnats were swarming around me, so I hurried with the work and got off the roof. I did wrap each pair of wires with electrical tape and I thought I had the wire caps on pretty tightly.

Anyone have any thoughts as to what may be causing this behavior? I find it strange that it works normally from 6:30 pm or so until the next afternoon, but it's getting up into the 90s everyday, so i've gotta fix it.

Could it be the sun heat itself, affecting the electronics somehow? I have noticed in the past that breakers seem to trip more easily during the hottest part of the day.

I did also spray the coils with coil cleaner

I wonder if I should go back and rewire the motor again, and\or, cover the a\c shroud with some sort of reflective material, in an attempt to deflect some heat.

Thoughts are appreciated!

Edit:  Inside my camper, the square area on the ceiling where the filter is, this area will drip water when the a\c is working (I recently learned i'll need to get on roof and clean the small drain line)
During the day when the a\c works randomly, this dripping will not occur, but in evening when the a\c stays on and runs normally, the dripping comes on full force. I don't know if this is somehow related to the compressor problem, but thought I'd go ahead and mention it.
Click to expand...

[I did also spray the coils with coil cleaner]

Did you rinse the coil with plenty of water after you sprayed on the cleaner? Another thing to check is make sure the motor is turning the correct way, and the wheels are installed the correct way. If for any reason, you aren't getting the correct amount of air thru the coil, the head pressure will be so high that the compressor will kick out on high pressure or the internal over load.
 
Rene T said:
I'm just curious as to why you replaced the fan motor.
Is this a new RV or new to you RV? It may help with other questions in the future if you go into your profile and create a signature of yourself telling us a little bit about you.
Click to expand...

I replaced the fan motor because the old one had burned out, so there was no a\c at all. I installed the new one in the same way that I saw the old one set up.
 
Ghostman said:
Are you sure it is blowing the right direction? The air should be blowing through the coils.
Click to expand...

When it's working, it's blowing cool air through the vents in the camper - wouldn't that indicate that it's blowing in the right direction? Thanks for input  :D
 
You have a blower fan and condenser fan on top. I didn't know which motor you replaced. Is it one motor that runs both or two different mitor fans. If it is one motor maybe the fan blades came loose on condenser side. Just throwing out some ideas since it started after the motor faliure replacement. I would just climb up and see if you are getting air through your coils.
 
It's been partially cloudy today, with clouds often blocking the sun - so the a\c has worked normally without shutting off
strange  :eek:
 
All air conditioners have a temperature where they stop working.  The internal freon pressure (head pressure) rises with temperature and eventually gets to a point where the compressor can't pump against it so the motor overheats and shuts down.

Since yours is cutting out at a relatively low temperature, that says something is raising the system pressure higher than normal when it gets hot.  It could be a plugged or oxidized condenser (the outside radiator) that's not as efficient as it used to be at getting rid of heat.  Cleaning the fins can help restore airflow, but make sure to get both sides and verify  the fins aren't oxidized as that alone transfers heat less efficiently than clean metal.  Make sure the fins are vertical and not bent over as bent fins stop the airflow and effectively shuts down that portion of the radiator.  Hardware stores have condenser fin combs you can use to straighten bent over fins.

As a temporary measure to restore cooling, you can set up a water sprayer to soak the condenser and lower it's temperature to keep the a/c running during the hot spells.  This is also a good way to test if the outside condenser is the cause of the high temperature shutdown, i.e. if the water cools it enough to let the a/c keep running.  But this will eventually kill the air conditioner because the condenser isn't replaceable in an RV a/c and any minerals in your water will build up on the condenser as the water evaporates, plugging up the airflow sooner or later.

 
vagabonds_moon said:
My rooftop a\c unit , the compressor is cycling off and on at random points during the day - but only at certain hours: from about 6:45 pm, when my camper is covered in shade, the a\c runs normally until about 12:30 the next afternoon, when it starts to shut off and on again. The fan will continue to blow air, but it's not cool - i'll hear the compressor come back on, and it'll start to blow cold.
Click to expand...
One of my two 6-year-old Dometic Penguins is doing pretty much the same thing. On for 3 (or 10) minutes, off for 3 minutes, over and over. My 2nd AC is working fine and both units exposed directly to sunlight.

Electronics?
 
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