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Old 05-04-2017, 04:01 PM   #1
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AC icing up

I'm hoping for some perspectives on what's going wrong with my AC, which is icing up. Here are the details.

Last summer, it worked great. It's a 2015, ducted, and last summer was my first season using it to cool.
This summer, it cools for the first 60-90 minutes, but ice forms on the unit, which I can tell because there is no condensate via the weep tube. Then the ice layer becomes too much, and cooling fails.
If I turn on the heat pump to clear the fins, I get a flood of water via the weep tube (so the tubes are not blocked), and once the ice is off the unit, I can turn it to cool again for another 60-90 minutes.
When it's cooling, the humidity in the cabin goes from 55% to 30%. It goes back up while the heat pump is on (if I manually switch it to clear the ice), then it descends again to 30% when I turn the AC cool mode back on.

I've tried High fan speed only, on the theory there wasn't enough airflow, but it was fine on low last summer. And whether I use Hi or Low this time, it still ices up.
Visual inspection shows nothing obvious blocking airflow, either inside or out. The interior air filters are clean. It's pulling air through the intake vents OK.

I called the dealer who said there were some bad compressors in 2015. But if it's cooling and heating, would that really indicate a bad compressor?

And a local mobile repair person said he doesn't work on them, (but he'll replace them with new units), because Dometic units don't allow for a recharge if you lose the coolant. Is that accurate? Seems odd to me.

The air temperature coming out of the vents while cooling is 12-15 cooler than the air going in.

Complicating this is the fact I'm full-timing, and not wanting to tow it to a dealer. I'd want a mobile repair person, so it would be great to have an idea of the problem before setting up the repair...

thanks!
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Old 05-04-2017, 05:21 PM   #2
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Quote:
Originally Posted by lbdesign View Post
I'm hoping for some perspectives on what's going wrong with my AC, which is icing up. Here are the details.

Last summer, it worked great. It's a 2015, ducted, and last summer was my first season using it to cool.
This summer, it cools for the first 60-90 minutes, but ice forms on the unit, which I can tell because there is no condensate via the weep tube. Then the ice layer becomes too much, and cooling fails.
If I turn on the heat pump to clear the fins, I get a flood of water via the weep tube (so the tubes are not blocked), and once the ice is off the unit, I can turn it to cool again for another 60-90 minutes.
When it's cooling, the humidity in the cabin goes from 55% to 30%. It goes back up while the heat pump is on (if I manually switch it to clear the ice), then it descends again to 30% when I turn the AC cool mode back on.

I've tried High fan speed only, on the theory there wasn't enough airflow, but it was fine on low last summer. And whether I use Hi or Low this time, it still ices up.
Visual inspection shows nothing obvious blocking airflow, either inside or out. The interior air filters are clean. It's pulling air through the intake vents OK.

I called the dealer who said there were some bad compressors in 2015. But if it's cooling and heating, would that really indicate a bad compressor?

And a local mobile repair person said he doesn't work on them, (but he'll replace them with new units), because Dometic units don't allow for a recharge if you lose the coolant. Is that accurate? Seems odd to me.

The air temperature coming out of the vents while cooling is 12-15 cooler than the air going in.

Complicating this is the fact I'm full-timing, and not wanting to tow it to a dealer. I'd want a mobile repair person, so it would be great to have an idea of the problem before setting up the repair...

thanks!
lb,

You are on the right track, but there are more issues with evaporator freezing than simply air flow across the evap. coils.

One major issues tha many neglect is improper mixing of return air with cooled exhaust air. If the return ducting is not properly sealed and this return air mixes with the cooed air exiting the eval. area of the unit, freezing can quickly occur.

In addition, every Dometic unit has a freeze sensor probe that should be placed directly into the eval. coils. Some are never properly placed by the installing tech and some fall out. That would be the first thing I would check with the separation of return and exhaust air next.

Also, while you have the eval section opened, I would definitely use a quality coil cleaning spray (available from any good A/C supply house) and clean bot the condenser and evaporator.

After doing the above (hopefully you found an issue), button it back up and see if you have it fixed.
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Old 05-04-2017, 05:26 PM   #3
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As for the "replace, not repair" statement, it is entirely correct. Nobody repairs most a/c unit issues, such as low refrigerant or bad compressor. A bad fan motor or some electronic componets are replaceable.
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Old 05-04-2017, 07:30 PM   #4
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lb,
One major issues tha many neglect is improper mixing of return air with cooled exhaust air. If the return ducting is not properly sealed and this return air mixes with the cooed air exiting the eval. area of the unit, freezing can quickly occur.

In addition, every Dometic unit has a freeze sensor probe that should be placed directly into the eval. coils. Some are never properly placed by the installing tech and some fall out. That would be the first thing I would check with the separation of return and exhaust air next.
Thank you! it's a total rat's nest of wires up in the ceiling, between the pretty intake covers that hide the mess, and the AC unit. I was surprised to find so many electrical wires criss-crossing this area, which means it's not sealed, otherwise how would the wires penetrate it? One of the wires is hanging down, and looks like it could be a probe. I'll examine it again.

And it does strike me that the entire cavity behind the intake covers is not sealed. Though it would be no less sealed this year than it was last year...
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Old 05-04-2017, 07:32 PM   #5
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One other possible bit of info:
I'm parked in full sun. When it's 82 inside and I turn the AC on, it's still just 70 outside. Could it be too cool outside for proper AC function?
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Old 05-04-2017, 08:22 PM   #6
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Old 05-04-2017, 08:28 PM   #7
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Sorry, it was not allowing images from my server.

Could this be the probe? There is a wrinkle/gap in the fins up in there where a probe might have been inserted, held in only by friction?
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Old 05-04-2017, 09:15 PM   #8
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Sorry, it was not allowing images from my server.

Could this be the probe? There is a wrinkle/gap in the fins up in there where a probe might have been inserted, held in only by friction?
Sure looks like a freeze sensor to me. Just jam that little device right back where it came from and hopefully, your problems will be solved.

I wold also check the separation of the return air from the cooled air blowing into the ductwork.......very important also!!!
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Old 05-04-2017, 09:49 PM   #9
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Fantastic! Thanks Lew!
Can hardly wait to try the AC tomorrow!
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