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Old 08-23-2008, 10:51 AM   #1
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AC frosting up

My AC is frosting up occasionally since I got back in Lawton. It didn't used to do this (I think). Most of the time it is cooling fine. Has it probably been frosting up all the time and I just didn't notice, or is something sinister afoot?
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Old 08-23-2008, 11:37 AM   #2
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Filter may need cleaning. Fan is slowing down and not circulating enought air through the evaporator. If there is a frost sensor in the evaporator coil (newer models) it may have gone south or must be repsitioned so it detects frost build up sooner and turns off the compressor to defrost the evaporator. It will automatically turn the compressor back on.
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Old 08-23-2008, 11:59 AM   #3
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Coils could be very dirty as well. The filters on mine (the original Armstrong) are not very efficient and allow for junk to build up on the coils. It took some doing, but I finally got most of it out.

Let us know what you find....

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Old 08-23-2008, 12:01 PM   #4
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I am not an HVAC guy but what little I do know I would start with Air cirrculation , check for nests leaves or other debri. Even say rain then dusty condition cause mud in coils. I made a device that connect to the garden hose and has a small copper tube 1/8 inch or so. I will blow the coils out with a small weak stream of water. I have blown fuses because of clogs/ lack of air flow. Or The commpressor is low on Refridgerant, causing not to run/ cycle properly. Good luck I am intrested on what your cause is
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Old 08-23-2008, 10:18 PM   #5
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Low gas would cause the evaporator to not get as cold as it should. If the unit is gettng cold the condenser most likely is not clogged with leaves or nests. That would cause the unit to not cool well because it could not dissapate the heat from the condenser. The Evaporator may be dirty caused by poor filtering. If all that is found OK look for the defrost thermostat to be faulty and is found embedded in the fins of the cooling evaporator.
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Old 08-24-2008, 06:33 AM   #6
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The inside of an RV normally has a higher humidity level than the out side(cooking ,showering,breathing) so if your AC does not have the sensor to prevent freeze up this could be the issue.This usually happens when you have the Thermostat cranked up as cold as it will go.Try dialling back the thermostat setting a little.

Just another 2 cents.
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Old 08-24-2008, 08:06 AM   #7
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Ice forming on the evaporator coils is generally caused by low refrigerant. As a quick and dirty rule, the temp of the evaporator is about 10 degrees warmer than the pressure in the evaporator. Not always, but we'll assume so for this example. If the pressure in the evaporator while running gets below 22 psi, it can become cold enough to freeze the condensation formed.
If you run the air conditioner on high fan setting, it will aggravate the problem (the higher fan setting will cool the hot compressed freon, and lower the temp of the low side freon as well). Try cleaning the coils and filter, and running the a/c on "low" setting. If it still ices up, you likely are low on refrigerant (R22). If you're lucky enough to have one of the Armstrong a/c units, it probably has a service port to add refrigerant. The trick will be finding an a/c guy willing to crawl on your roof to charge it.
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Old 08-24-2008, 09:08 AM   #8
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another clue

I have noticed that the icing tends to happen overnight when I have it set on the lowest (warmest I guess would be better) setting.
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Old 08-24-2008, 10:22 AM   #9
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I have a 2 year old Penguin. It froze once last year and once this year. Both in on max fan and cold settings. These were both situations where I ran it longer than usual in higher than normal temps and humidity. I will try backing off a bit.

Dumb question: When my unit reaches the approppriate cold setting and the AC cooling shuts off, the fan keeps running should it?
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Old 08-24-2008, 10:31 AM   #10
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That is carey. I run mine full bore. Never froze up. Duo Therm Dometic penguin. No difference. If it freezes there is another issue. Running it on different speeds adn documenting the results is a great way to zero in on the problem. Not live with it.
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Old 08-24-2008, 10:33 AM   #11
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It's low on refridgerant, no doubt about it!
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Old 08-24-2008, 08:59 PM   #12
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Quote:
Originally Posted by Lumatic

Dumb question: When my unit reaches the approppriate cold setting and the AC cooling shuts off, the fan keeps running should it?
Yes, unless you have a remote thermostat, and it is capable of turning off the fan when desired temp is reached.
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