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Old 05-21-2013, 10:14 PM   #1
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Air Conditioner Freezing up... I think...

First of all, is it normal that 100 things go wrong all at once right before a big trip? ANYWAYS... we have 2 old Duo-Therm 590 air conditioners on our motorhome. They both produce ice cold air. The one up front however, I think has a problem with the freeze control... or it could be the the circuit board. I don't know...

Basically what I think is happening is the freeze control doesn't ever shut the pump off until after the system is already frozen up, which locks up the compressor. This in turn wreaks havoc on my generator and the circuit breakers when it tries to turn back on a couple minutes later.

I'm going to try switching the freeze control switch from the back air conditioner with the front one and see if that fixes the front a/c... if it does then maybe I can just get a new freeze control switch. Does anyone know where I can get one of these?

The ac control box has the part number 3104999. I have not had any luck searching that number on the net. The air conditioner model # is 59016.521 and is a Duo Therm 590 quick cool. If anyone can help me out by pointing me in the right direction here I would greatly appreciate it...

cheers
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Old 05-21-2013, 10:38 PM   #2
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You might give Duo Therm Parts for Air Conditioners for Sale - PPL Motor Homes a call, they sell parts for Duo-Therm A/C.

I'm sure you've cleaned the fins and filters so air isn't restricted. Here's a link to a 'Mr. Fixit' page about the 590.

http://www.fixya.com/search/p1251696...ick_cool_ac_rv
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Old 05-22-2013, 05:25 AM   #3
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Thanks for the input... It doesn't look like PPL carries anything in the Quick Cool line. Figures... 20 year old A/C.

I also wanted to add that at one point about a week ago, I think a relay on the control board must have been stuck closed and the compressor wouldn't shut off even when you turned the unit completely off and the fan wasn't running. I'm guessing it's a board issue, and not just as simple as replacing the freeze protection switch. That figures too...

If I can't find a replacement control board, I'm guessing I'll have to replace the thermostat and the control board and probably even pull new wires. I'm not even sure it's possible to pull new wires, but maybe I can get away with just wiring new plugs on the ends of the existing wires. Anyone have any suggestions on a new thermostat/control board combo?

I'm going to send an email to Duo-Therm or Dometic or someone today to see if I can get some help.

Thanks again.

cheers
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Old 05-22-2013, 08:14 AM   #4
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The AC unit might be low on Freon (or whatever refrigerant it uses). It's typical of a unit to freeze up when it looses part of it's charge.

As for 100 things going wrong the rule of thumb is: If you put it in the driveway less than 24 hours before you expect to leave at least 100 things will fail to work properly. If you put it in the driveway a week in advance of the pending trip nothing will go wrong until 24 hours AFTER you pull out.
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Old 05-22-2013, 11:02 AM   #5
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Well, I've never heard of an A/C having freezing issues because of a lack of refrigerant... my experience as always been that when an A/C system is low on refrigerant it doesn't make any cold air.

The air from both conditioners is ice cold... actually probably colder than it should be due to what I think is a not so great design of the ductwork. (about 45 of differential) It just doesn't allow good airflow because the passages are too restrictive. I did clean both air conditioners out on the evaporator and condenser sides of the system. The issue with freezing has to be the board or the freeze protection switch. If that part of the circuit was working properly there should never be an instance where you freeze the compressor, although transfer of heat to the outdoors will definitely suffer if your evaporator and condenser are dirty.

cheers
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Old 05-22-2013, 11:10 AM   #6
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Quote:
Originally Posted by Piker View Post
Well, I've never heard of an A/C having freezing issues because of a lack of refrigerant... my experience as always been that when an A/C system is low on refrigerant it doesn't make any cold air.
It's a VERY common cause. Unless you add piercing fill valves to the A/C system, you can't refill rooftop A/C, and if you do, the valve will probably leak soon in the future. Did you call PPL and ask for a substitute part or just look at the online catalog? The catalog is often limited.

Why is your AC unit freezing up

Why does low freon cause an air conditioner's coils to get colder? - Yahoo! Answers
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Old 05-22-2013, 02:12 PM   #7
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Quote:
Originally Posted by Piker View Post
First of all, is it normal that 100 things go wrong all at once right before a big trip? ANYWAYS... we have 2 old Duo-Therm 590 air conditioners on our motorhome. They both produce ice cold air. The one up front however, I think has a problem with the freeze control... or it could be the the circuit board. I don't know...

Basically what I think is happening is the freeze control doesn't ever shut the pump off until after the system is already frozen up, which locks up the compressor. This in turn wreaks havoc on my generator and the circuit breakers when it tries to turn back on a couple minutes later.

I'm going to try switching the freeze control switch from the back air conditioner with the front one and see if that fixes the front a/c... if it does then maybe I can just get a new freeze control switch. Does anyone know where I can get one of these?

The ac control box has the part number 3104999. I have not had any luck searching that number on the net. The air conditioner model # is 59016.521 and is a Duo Therm 590 quick cool. If anyone can help me out by pointing me in the right direction here I would greatly appreciate it...

cheers
Before you start replacing things, try to determine if the freeze sensor is operational. If it is not working, and the A/C unit is freezing, you will need to fix 2 things. The freeze sensor detects a too cold condition in the intake and cycles the A/C off. If this were to occur you would need to find out why it is detecting a freeze. The most common cause in RVs is a mix of cold refrigerated air (the output) with air in the intake side of the A/C. This occurs in the interior airbox when seals fail .... typically, the foil tape has lost it's adhesion. You can sometimes find it by removing the grill and filter and sticking your hand in the opening. If you feel COLD air (rather than warm moving air) it's leaking across the baffle from the output side. This condition causes a freeze and what is known as a "short cycle". Fixing the air leak usually stops the freeze condition ... but that doesn't explain why the freeze sensor didn't shut down the system.

RV A/C works more like a window A/C than home central air. The cold and warm air essentially share the same "hole" separated by a baffle.

see here for bad seals/tape and collapsed ductwork:
A/C Ductwork collapse and rehab
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Old 05-22-2013, 02:20 PM   #8
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There are only 2 reasons an A/C will freeze. Low on gas and lack of air across the evaporator. A 20 year old unit may not have a low pressure switch that shuts the compressor off when low on gas. The compressor should be able to run continuously without freezing.
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Old 05-22-2013, 02:36 PM   #9
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Originally Posted by jettyjock View Post
There are only 2 reasons an A/C will freeze. Low on gas and lack of air across the evaporator. A 20 year old unit may not have a low pressure switch that shuts the compressor off when low on gas. The compressor should be able to run continuously without freezing.
From Dometic/Duo-Therm:

A5. Air Box
Improperly installed, the air box can be a source of cooling
problems. The air box must be sealed to the ceiling template
to prevent the mixing of discharge and return air. This
will cause short cycling or frost formation on the inside coil.

C22i. Short Cycle
Air Distribution Box Installations
Short cycle is caused by cold air being drawn back into the
intake side of the air conditioner before it is mixed with the
warmer room air. This may cause the evaporator coil to
freeze up
, causing the cold control or the thermostat to
open the circuit to the compressor. Cold discharge air that
enters into the return air portion of the air box can cause a
false temperature reading at the thermostat and shut down
the compressor.
Two possible causes of this condition are the air box and
the discharge duct. If the air box is not sealed tightly against
the ceiling template, it will allow cold air to cross over into
the return air portion of the air box. Also, if the discharge
duct is not installed properly, it can allow cold air to cross
over into the return portion of the air box. Make sure you
have the correct discharge duct for the thickness of the
roof. Seal all problem areas as necessary. You may need to use tape
to seal the discharge duct. Also, make sure the discharge louvers
are not restricted.
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Old 05-22-2013, 04:02 PM   #10
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First of all, thanks to everyone for all the help... I've learned quite a bit about A/C that I didn't know before this thread. The fact that low charge can cause icing problems just blew me away. Good information to know.

Second of all... I have to apologize for being rather ignorant about how an air conditioner freezes, and thus unintentionally misleading you all on what my problem actually is. I didn't realize that when an air conditioner freezes up it actually produces ice on the evaporator... I thought it froze up internally. I'm really sorry for making you all think I had an icemaker, but I've never seen a stitch of ice or frost on the evaporator.

So at this point, I guess I'm not really sure what the problem is. The A/C makes good cold air, but for some reason after it's run for a while it wants to start tripping breakers when the compressor cycles on. I don't understand... unless the control board is malfunctioning and short cycling the pump. Like I said, I had some issues with the compressor staying on when I turned the switch off at the thermostat... which makes me think I have a control board issue. The bad thing about that is that Duo-Therm told me today that I would have to replace the thermostat and control board with a newer version since this one isn't available any more... plug ends would have to be adapted also. I'm not saying I won't do that, but I'd like to be certain of what the problem is before I spend a couple hundred bucks on new controls for a 20 year old air conditioner.

I tell you... I'm starting to think that RV stands for something other than Recreational Vehicle... like maybe "Ruins Vacations." lol. Not really... I'll get through this, but it's been a long haul getting things fixed up over the last year... ready for some camping instead of fixing and spending money on repairs.

thanks again...

cheers
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Old 05-22-2013, 04:20 PM   #11
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You may find this helpful:
http://bryantrv.com/docs2/docs/acservice.pdf
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Old 05-22-2013, 04:25 PM   #12
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I don't know of any 19 year old that doesn't needs upkeep and sometimes a slight correction. By the time you add up all the parts you're going to need, it might be smarter to just replace it with a new A/C. Even if you get the old one working, it's still old.
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Old 05-22-2013, 05:40 PM   #13
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I don't know of any 19 year old that doesn't needs upkeep and sometimes a slight correction. By the time you add up all the parts you're going to need, it might be smarter to just replace it with a new A/C. Even if you get the old one working, it's still old.

Pretty much the way I feel about RV reefers and HW heaters too ....
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Old 05-22-2013, 06:41 PM   #14
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90% of the freeze up problems with an RV A/C is low air flow. When was the last time you cleaned the filters and the evaporator coil. Also run the fans on high speed, not low speed. Next check for air bypassing in the unit or other restrictions.

Run the unit on high for at least 15 minutes with the t'stat cranked to a lower temp to keep the compressor on. Check the air inlet to the unit and the air outlet as close to the unit as possible. The outlet air should be 18 to 20 degF colder than the inlet air. Any thing beyond these numbers indicated a problem.

If it is really low on refrigerant, this is expensive to fix properly as the unit is hermetic and not easily accessed.

For a unit 10 years old or more, I would not spend much money on repairs and get a new unit.

Piker, yes, low refrigerant charge can cause freeze ups. The reason is if you are low on refrigerant, the compressor does not have enough gas generated by the limited amount of refrigerant. This causes the evaporator pressure to drop which also means a lower temperature in the evaporator. It will drop below freezing in the coil, but if you check the compressor suction temperature (superheat) it will be higher than normal.

Ken
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