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Old 15-05-2013, 17:06   #1
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Looking for suggestions on AC problem

We have a 3 year old Dometic Marine Air 16000 BTU AC. We have been having a problem where the coils are freezing up which eventually leads to the system freezing up to where it doesn't even cycle air.

We had an HVAC guy look at it about 3 weeks and he checked the pressure and for leaks and didn't find any problems. He charged it up anyway.

The unit works fine at night and all night long until later in the morning when the outside temperature begins to climb. We then have to reverse cycle it to heat until the unit defrosts and then we can start again. It seems that the head unit isn't kicking on the defrost cycle during the day but it does in the evening and night. We are thinking it is a bad head unit.

Any suggestions besides calling out the HVAC guy again?

Thanks
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Old 15-05-2013, 17:33   #2
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Re: Looking for suggestions on AC problem

Don-
Take a look at air flow across the evaporator coil. If memory serves, reduced air flow will cause the condition you described.
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Old 15-05-2013, 18:41   #3
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Re: Looking for suggestions on AC problem

Low air flow is likely your problem. First check if the filter is clogged!!! Or maybe the air is short cirucuiting- the return air is mixing with the discharge air.

Then it may take a ducting fix. The air exiting the evaporator must be at least 6" and if it branches after that, one of them can be 4" and the other must be 5".

BTW the tech who came out and checked freon levels probably doesn't know what he is doing. Don't use him for the fix.

David
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Old 15-05-2013, 18:51   #4
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Checked for pressure and leaks and found no issue why did he charge it? Did he do a recovery and vacuum before charge? Agree check the air flow. Are there any dampers on exhaust. Anything that couls restrict flow at the intake. Fan operating properly? Coils clean etc.....
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Old 15-05-2013, 19:06   #5
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I would look into a possible stuck or defective expansion valve. Most ac systems use a thermally controlled valve which helps prevent evaporator icing. Additional air flow will slow this issue down but not cure the problem.

And yes I agree, find another ac tech!
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Old 16-05-2013, 07:21   #6
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Re: Looking for suggestions on AC problem

The air flow seems okay, but I'll clean the coils again. I keep the filter clean. We checked the ducting and all was fine there. This worked fine for 3 years so I can't figure out what has changed.

Thanks all, and nice to hear from you Charlie!
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Old 16-05-2013, 15:41   #7
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Re: Looking for suggestions on AC problem

Quote:
Originally Posted by ReMetau View Post
We have a 3 year old Dometic Marine Air 16000 BTU AC. We have been having a problem where the coils are freezing up which eventually leads to the system freezing up to where it doesn't even cycle air.

We had an HVAC guy look at it about 3 weeks and he checked the pressure and for leaks and didn't find any problems. He charged it up anyway.

The unit works fine at night and all night long until later in the morning when the outside temperature begins to climb. We then have to reverse cycle it to heat until the unit defrosts and then we can start again. It seems that the head unit isn't kicking on the defrost cycle during the day but it does in the evening and night. We are thinking it is a bad head unit.

Any suggestions besides calling out the HVAC guy again?

Thanks
He didn't fix it the first time? Just added refrigerant?

Restricted air flow is one cause of coils icing up but the HVAC technician should have checked that. An undersized AC or too much heat gain will do the same thing. If you have a lot of sunlight and heat coming in through the windows you could have this problem. Tinting your windows might help. Get the high tech heat reflecting tint installed.

Your thought that the defrost cycle works at night but not in the daytime doesn't make much sense. The AC doesn't know if it's day or night.

I say call the guy and tell him that he didn't fix the problem.

BTW: If there were no leaks but the refrigerant was low, it could have leaked into the cooling water in the heat exchanger. If the tech finds it low on refrigerant again (assuming it was low the first time), this may be your problem. Ask him about it. I had that problem and it's unrepairable. I had to replace the unit.
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Old 24-05-2013, 15:45   #8
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Re: Looking for suggestions on AC problem

I put a small fan in front of the head unit almost a week ago, and have not had a frozen system yet. I think I may need to get a remote thermometer for the head unit. Strange thing is that it worked for about 3 years where it is.
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Old 24-05-2013, 16:12   #9
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I am having the exact same issue with one of my units. I am thinking I am experiencing the same thing, sun beating right on the panel during the day may be causing it to run continuously and not cycle off regularly. You may be on to something here...
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Old 24-05-2013, 23:39   #10
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Re: Looking for suggestions on AC problem

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..., sun beating right on the panel during the day may be causing it to run continuously and not cycle off regularly....
I was told by our Dometic engineer not to run it during the day because the size of the unit (12,000 BTU) will never overcome the heat of the day.
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