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Old 07-15-2012, 08:45 PM   #1
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AC Problems in 2011 28bh Grey Wolf

Hi All,

I went camping this week and my AC started doing something very weird. On our last day the AC compressor would stay running for a few minutes after the blower would kick off. I also noticed when the blower would kick back on the compressor would not kick on for a few minutes after the blower. Then it would do the same thing every time. I am an Electronic Technician and have been for many years, but very little knowledge in the AC area. I believe the problem is with the thermostat but I am not sure. Also when I ran the blower constantly the unit would freeze up. This is the second thermostat I install in this RV. The first would not cool the RV. Any help or suggestions would be appreciated. The unit and thermostat is a Dometic.

Thanks in advance.
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Old 07-15-2012, 09:17 PM   #2
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i know enough abt refrigeration to get me in trouble.
when i bought my trailer, i was told if u opened the vent on the bottom (quick cool) that it would freeze up.
i tend to think it is the thermostat also. just don't understand how 2 can be bad.
see if u can find the schematic on it. it is probably near where the a/c wires go in. see if u can find any control within the unit. all i know abt is a thermal overload inside the compressor and a low pressure switch to keep the compressor from running w/o (or low) freon.

does the air flow seem to be normal? if the fan is slowing down, it could cause the freeze up.

Before i get too far into left field on this, by any chance is it a heat pump?
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Old 07-15-2012, 09:30 PM   #3
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Hi JIMH,

No it's not a heat pump. The unit was not on quick cool, I figured since the compressor was staying on I would leave the blower on constantly but it would freeze up like this. It would work OK with it on the cycle setting. The air does flow fine. Also the first thermostat would not bring the temp down enough, so this is why I changed the first thermostat.
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Old 07-15-2012, 11:04 PM   #4
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i would try a mechanical thermostat (bimetal strip) and see if it solves it. i don't know of any other controls. (i know others exist within the unit but don't have a schematic to see how they work).
i thought when i reread it i would find that the compressor comes on then the fan. then when thermostat calls for shut down, the compressor shuts down then the fan. that more like the home units work. urs, the compressor runs w/o the fan both ways.
the iceing part, i can't figure; that is usually low air flow and/or low freon. Was hoping that someone with more experience with these units would chime in.

If my unit is running continuous, i noticed the compressor will kick off for a few minutes every so ofter (maybe every half hr or so). i know the thermostat is still calling for cool. (the fan is in auto and doesn't shut down) sense it continues to cool, i haven't been too concerned with it. never have been curious enough to try and figure it out.
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Old 07-26-2012, 02:43 PM   #5
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Fan doesn't match compressor

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Originally Posted by daavalanche View Post
Hi All,

I went camping this week and my AC started doing something very weird. On our last day the AC compressor would stay running for a few minutes after the blower would kick off. I also noticed when the blower would kick back on the compressor would not kick on for a few minutes after the blower. Then it would do the same thing every time. I am an Electronic Technician and have been for many years, but very little knowledge in the AC area. I believe the problem is with the thermostat but I am not sure. Also when I ran the blower constantly the unit would freeze up. This is the second thermostat I install in this RV. The first would not cool the RV. Any help or suggestions would be appreciated. The unit and thermostat is a Dometic.

Thanks in advance.
It's not your thermostat (99.9% thermostats DON'T fail), Depending on the AC unit you have here is how it should work.

Thermostat sends cooling call
Fan on immediately
Compressor on immediately (Some systems have a 10 sec time delay to reduce power surge).

Thermostat turns off
Fan off immediately
Compressor off immediately

If this is not the sequence you may have a relay with sticking contacts or a loose wire.
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Old 07-26-2012, 03:00 PM   #6
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My compressor delays and kicks on probably 5 seconds after the blower then on occasion it will run and the compressor will kick off for 5 seconds and then come back on. I think that's just how they operate. Mine cools great.

As for the t-stat those stats don't like real hot weather so sometimes if it is super hot you have to take a can of compressed air, turn it upside down and blow it on the stat to cool it for the AC to kick on.
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Old 07-26-2012, 03:08 PM   #7
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Compressed air

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My compressor delays and kicks on probably 5 seconds after the blower then on occasion it will run and the compressor will kick off for 5 seconds and then come back on. I think that's just how they operate. Mine cools great.

As for the t-stat those stats don't like real hot weather so sometimes if it is super hot you have to take a can of compressed air, turn it upside down and blow it on the stat to cool it for the AC to kick on.
If your hot and the AC cycles off why don't you just turn the thermostat down a couple degrees?
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Old 07-26-2012, 03:10 PM   #8
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Originally Posted by HVACretired View Post
If your hot and the AC cycles off why don't you just turn the thermostat down a couple degrees?
I'm not hot. It cools fine. If it runs for say 20 minutes straight then on occasion the compressor will kick off for 5 seconds and go back on while the blower remains on.
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Old 07-26-2012, 03:15 PM   #9
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I'm not hot. It cools fine. If it runs for say 20 minutes straight then on occasion the compressor will kick off for 5 seconds and go back on while the blower remains on.
Something is bad wrong it should not do that, have you checked the outside coil on the roof to make sure its not clogged with cotton wood seedlings (pull the cover off and look at the outdoor coil surface and between the fins) or something else?

You compressor should never short cycle
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Old 07-26-2012, 04:57 PM   #10
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Well first things first is your unit controlled by the wall thermostat or does it have analog controls secondly if you have a wall thermostat controlling the unit is it electronic or non electronic, these units incorporate a control relay box if its controlled by the wall thermostat that is located up in the main unit either up on top outside under the cover or up in the ceiling plenum in the return air. these control boxes have a probe that is supposed to be wedged into the evaporator, this is a safety device to prevent the unit from over cooling and icing up so that the gas returning to the compressor doesn't liquefy and destroy the compressor and it also has three relays, one for the compressor and two for the fan speeds which sounds like they are working fine, the short cycling could be caused from the capacitors. There are two of them, one is for the start up and the other is for the run, depending on the configuration they might be separate or combined into one. If you have been running this unit in extreme heat the capacitors might be starting to fail as they cant cope and will fail eternally or burst, this is usually caused from low voltage and high heat and as a rule of thumb when voltage falls below a certain point the amperage climbs and that's what kills capacitors. I would get the unit inspected for the control box and the capacitors
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