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Old 05-15-2016, 07:55 AM   #1
ksstick
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AC Vent Temps 15 BTU Dometic

Hello
My Ac doesn't seem to be working properly
The temperature at the vents are only 60 degree and outside temp was 74 degrees
Yes at the vents and AC are clean?
Can I assume it is low on Freon? I was told most places donít work on the AC unit, just replace them.
Any thoughts?
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Old 05-15-2016, 08:17 AM   #2
canesfan
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RV AC units are "closed" systems (although some will argue that point) and because of that you can't add freon, if, in fact, that is what is wrong. I don't know what temp the air coming out of the vents "should" be.
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Old 05-15-2016, 08:25 AM   #3
Bob Landry
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First of all, outside ambient temp is irrelevant to determining proper AC operation. The fact to observe is the "split across the coil", IE temperature difference between the return air and discharge air. A difference of 18-20 degrees indicate proper cooling. This figure can be misleading if the unit has dirty filters which would restrict air flow or is simply undersized for the space it's cooling. So this number is really only valid if everything is as it is supposed to be.
A temperature measurement directly at the supply air output of upper 50s to 60 degrees would indicate a properly functioning unit. If you go on top and remove the AC shroud, the suction line sweating back to the compressor would also indicate that the unit is properly charged. Charge can also be checked by measuring the compressor amp draw and that has been discussed in previous threads.
If you are reading 60 degrees at your vents, and the trailer is not being cooled, your unit is probably undersized. I would also check the plenum, and vents for leaks that may be pumping air into your ceiling.
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Old 05-15-2016, 10:16 AM   #4
Ken / Claudia
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I agree with Bob, the a/c units are made to reduce the air they intake by 20 degrees F at best. Even the Keystone manual as lacking as it is lists that information.
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Old 05-15-2016, 01:08 PM   #5
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I'm not an AC tech by any means. I have a 2014 Dometic 15k AC. I'm sitting in the panhandle of FL and the outside temp is 87. My ducts read 48 degrees to 51 degrees with an infrared temp gun. Don't know what that really tells you. How old is the unit/ducts/etc. etc.? Maybe it just needs a little TLC.
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Old 05-15-2016, 05:00 PM   #6
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Quote:
Originally Posted by ksstick View Post
Can I assume it is low on Freon? I was told most places donít work on the AC unit, just replace them.
Any thoughts?
Yea, for $700 or whatever they cost, they just get replaced. They're pretty easy to replace once you get them on to the roof.

If the compressor is running (you should be able to hear it) and you're only getting a 15 degree temp drop over the coils, something is wrong...
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Old 05-15-2016, 06:03 PM   #7
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Originally Posted by ksstick View Post
Hello
My Ac doesn't seem to be working properly
The temperature at the vents are only 60 degree and outside temp was 74 degrees
Yes at the vents and AC are clean?
Can I assume it is low on Freon? I was told most places donít work on the AC unit, just replace them.
Any thoughts?
The Air Conditioner is warrantied for 2 years. If I remember correctly, this month will be your second anniversary, so if you're having issues with your A/C, I wouldn't delay contacting your dealer and getting his advice about whether or not you can get warranty service before it expires!!!!!
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Old 05-15-2016, 07:10 PM   #8
ksstick
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the suction line back to the compressor is freezing up
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Old 05-15-2016, 07:45 PM   #9
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There should be a freeze sensor on the coils above the intake. Possible its fallen out/off? Some clip on some just push in between the fins.
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Old 05-16-2016, 09:05 AM   #10
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the suction line back to the compressor is freezing up
I would look for an air restriction, either dirty filters or a dirty evaporator. It could be a low charge, but the frequency of that happening on these units is low and they only take a pound or so of refrigerant, so if you do develop a leak, you would most likely lose the entire charge and there would be no cooling at all.
You have no way of checking for a correct charge except to measure the amp draw of the compressor and Dometic is going to require the shop to do that before replacing it under warranty.
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Old 05-16-2016, 09:12 AM   #11
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I'm not an AC tech by any means. I have a 2014 Dometic 15k AC. I'm sitting in the panhandle of FL and the outside temp is 87. My ducts read 48 degrees to 51 degrees with an infrared temp gun. Don't know what that really tells you. How old is the unit/ducts/etc. etc.? Maybe it just needs a little TLC.
An infrared gun is not going to tell you much. The outside temp is irrelevant since all of the air going through the coil is recirculated from inside. It doesn't draw in any outside air. The reading from the IR gun is affected by several variables. The size of the dot projected by the gun varies in accordance with the distance, it depends on exactly where on the unit you are reading, and most IR guns have a margin of error, usually up around 5%, so it is of little if any benefit for troubleshooting/checking ACs or refrigerators. It does an adequate job of checking for overheated axle spindles.
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Old 05-16-2016, 09:48 AM   #12
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As far as literal AC function I understand the outside temp is irrelevant, but, from a practical standpoint the outside has a lot to do with how the AC cools. Our black vent covers, AC shrouds, black windows etc. generate a ton of heat inside of the trailer; all of which the AC has to counter - the hotter it is the harder it has to work. At some point an x sized AC will not cool an x sized trailer simply due to the amount of heat coming into the unit and the limitations of the AC unit.....then you get a larger unit or 2nd AC Simplified I understand but those are factors.

At 50 degrees a +/- of 5% (2.5 degrees) is good enough for me with the infrared gun. It's also good enough for my heating/cooling contractor to use when diagnosing AC problems. The gun says its optimum reading range is 18" and that's what I used when reading the AC vents in the trailer. I do also use it for reading my wheels when traveling....much more accurate than putting my hand on the wheel/tire It's just a good way to get a quick indicator of what's going on; beats the heck out of hanging little thermometers in the vents, waiting for them to get to max cool and then trying to read them as I've seen done.
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