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Old 07-15-2012, 07:45 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, 08:17 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, 08:30 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, 10:04 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, 01:43 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, 02:00 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, 02:08 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, 02:10 PM   #8
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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, 02:15 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, 03:57 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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Old 07-26-2012, 10:43 PM   #11
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if u could open the covers and look at the relay and see if there is anything that might be touching or loose. i would also leave the covers off and watch the relays and see if the fan is relay is opening when the fan stops. (if u kill the 120 to the air conditioner, u can turn the thermostat on and hear the relays and located them (assuming they aren't readily visible).
there should be a wire (from thermostat) going to the fan relay and one going to the compressor relay (so u can run the fan w/o the compressor).
i've seen capacitors go out but they usually show some sort of distortion. i would question the cap going out due to low voltage. these items are usually voltage dependent to charge them. i wouldn't try to argue the point but it does raise a question.
i'm really stumped as to why the compressor would continue to run unless the fan motor is going out or the thermostat not calling for it to come on. a fan motor that isn't coming up to speed or becoming intermittent will cause very cold air to come out and a freeze up if compressor isn't shut down. (if it is severe enough, the compressor will shut down due to high head pressure either from a high pressure switch, if it has one, or the thermal overload inside the compressor).

if u have changed that thermostat in the past, double check ur wiring and make sure that something isn't touching where it shouldn't. make sure u have the wires connected to the correct terminal.

the freezing up really makes me question the fan speed. especially if the unit cools fine.
I believe RV wizard has the control perty well nailed. you may not find as many capacitors but that varies with manufacture and how they felt that day.

i would tell u just to change ur fan motor and see if it solves the problem but u may want to do a little more trouble shooting before throwing parts at it. make sure the relay itself isn't bad.
the fan on mine would run for a couple hrs then it would stop. the difference is that it would make a noise (i've had fan motors stop, but this is the first one ive seen that made a loud noise). the hour or two became 15 minutes then not come on at all. next day, it may work for an hour again. (bearings were good and not dry).
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Old 07-27-2012, 12:15 AM   #12
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I forgot to also say that there is a capacitor for the fan motor as well and the motor wont run unless the capacitor is present, if the motor is intermittently functioning in short cycles either the capacitor is going bad or the wingdings in the motor are shorting out due to overheating, if there is a smell of burning plastic or or discoloring in the winding to a dark brown the coil most likely has a short and is arcing inside.
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Old 07-27-2012, 01:12 AM   #13
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and well there's a third culprit lurking in the system and that is the themoststat slider, the Coleman Mach thermostat has a analog slider control that will start to malfunction because of dust contamination, let me put it another way remember the old battery operated transistor radios, how when you turn them on they would crackle up a storm well that's from dust or contact oxidizing and the only way you could get rid of it was to move the volume control up and down quickly to remove some of the contamination well the thermostat will do the exact same thing, by turning off the power to the upper unit then put the thermostat on cool and listen for a rapid clicking sound as you move the slider from say 80 degrees to sixty slowly if a rapid clicking sound is heard the problem is the contact strip in the thermostat is contaminated, I should also mention as well that cigarette smoke will foul it up too, if this is the case you can do one of two things
first is to replace the thermostat and go digital and install model #8530A345 which has open end wires. or you might try some contact cleaner which can be purchased at the Source in a spray can form, but CAUTION if you use this method as the saying goes { a little goes along way} if you dowse the slider you may end up washing away the silicon lubrication and that will render the thermostat useless and it will have to be replaced.
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Old 07-27-2012, 08:27 AM   #14
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Thanks everyone for all the responses. My first thought is it could be a relay sticking, but the unit seems to cycle OK. When the fan comes on, the compressor waits about 2 or 3 minutes now. When the fan kicks off due to temp change in the camper, the compressor stays on for 2 or 3 minutes after. Also I noticed this, with the thermostat off the compressor stays on for a few minutes. I have to turn off the breaker for it to stay off. When I returned home after this last trip, I plugged the camper in I turned the breaker on and the compressor came on. So it is sitting at this time with the breaker off.
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Old 07-27-2012, 10:04 AM   #15
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Smile Cool ideal Fix

Larry Cavens here
Sounds like you hit the jack pot!!!
So the only thing there is left to do is replace the control box which is in most cases up in the ceiling plenum
if the unit is still under warranty there shouldn't be any cost to you but if it isn't you're looking any where from 150.00 to 300.00 dollars depending on if you have just cooling/ or cooling with a electric heat strip combo
They're not that hard to re & re if you are mechanically handy, it will be either three quick dis connectable plugs or two dis connectable plugs and four dc wires that come from the thermostat/ or if you have the electric heat strip feature there will be five dc wires, I always if I can take pictures before hand so I have a point of reference to fall back on.
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Old 09-09-2012, 09:30 AM   #16
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Update,

I finally was able to get my RV in for service. They replaced the thermostat and AC control board. They said it was probably the thermostat but they replaced both just in case. Thanks for all the replies.
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Old 09-09-2012, 01:46 PM   #17
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sounds like they were covering all bases. glad u got it fixed.
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