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Old 05-26-2015, 12:29 PM   #1
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Angry Dometic 15,000 BTU A/C Failure

I was wondering if anyone had any experience with an issue i am experiencing.

Last week i purchased a 2016 Coachmen 320 BHDS Freedom Express Liberty Edition and when i picked it up, it was cold outside so we could not effectively test the A/C. We upgraded the A/C unit from the standard to the 15,000 BTU option.

Over the weekend the temperature in our area rose to 85 degrees and we went out to test out whether the upgraded A/C was worth it. The inside temperature of the trailer was 104. We turned on the A/C (set to 72) on HI (not AU) and after 45 minutes the air temperature output (not using the roof vents) was 90 degrees only cooling the trailer to 98 degrees. Then after a while the unit just shut off entirely, still in HI mode, restarting on its own in a minute or so.

additionally other times, the unit would sometimes just shut off completely and restart within a second.

It is hard to explain, but i was using one of those indoor/outdoor clock/thermometers to do the testing.

I made a video and posted it on YOUTUBE https://youtu.be/ORNxnCzuJWU
i was going to upload it here, but it seems to be too big to attach (currently at 800meg) I'll work on that and if anyone who is interested has trouble i'll see if i can reduce the file size.

if you watch the video, no silly comments about my narrative as it was very impromptu and not thought out in anyway.

Anyway, if anyone has any suggestions or advice, i would really appreciate it. Im not looking forward to taking it back to the dealer since they are over an hour away from me.


Dave
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Old 05-27-2015, 07:08 AM   #2
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My guess from your description:

1) Heat Load. By not opening a roof vent to let the hot air escape as the trailer filled with cold air (which sinks) you forced the air conditioner to try and remove ALL of the btus of heat in the camper. This will cause continuous operation of the compressor which, like any motor, will eventually will over heat and shut down. This is bad for the air conditioner's health.

2) Humidity. The air conditioner cools by two primary methods (in effect) by lowering the air temperature and removing humidity. Of the two, removing humidity is the most effective in you "feeling" cool. You will "feel" cooler in 80 degree air at 60% humidity, than in 80 degree air at 98% humidity.

To remove humidity, the air conditioner MUST cycle. Shut off and let the coils warm up so frost and ice formed during the ON cycle can melt and be removed via the roof drain. By setting the thermostat at 70 with an outside air temp at 80, you were doing a "good thing."

BUT, the air conditioner never got to see that outside 80 degree air because it was working with 104 degree air; see the importance of lowering the heat load?

3) Ice detector probe. There is supposed to be an ice detector probe in the cooling coils to protect the compressor. The probe detects icing and will shut the compressor down to clear it. The fan motor still runs but the compressor does not while the coil tries to warm up. Depending on how fast the ice accreted (built up), this could take a long time during which no cooling and low, or NO, air flow is coming out of the air conditioner regardless of fan setting.

4) Short Cycling (start up then shutdown in a few seconds) has several possible causes.

4a) Voltage is one. 15K BTU air conditioners draw many more start up amps than the 13.5K variety. If you are running the AC off of a small diameter extension cord for example (or low voltage at the source from a heavily tasked campground), the start up amps required can exceed the ability of the motor's internal thermal protection to handle. It can open and shut down the compressor well before 20 amp circuit breaker can heat up enough to open.

4b) An air leak between the intake and the forced air outlet sides of the air handler section. Note the metal tape in the frost sensor picture. If the leak allows a significant amount of hot air to bypass the coils, the frost detector will "think" the coils are frozen and will shut the compressor down. It will "immediately" reset (few seconds) and try to restart the compressor. HOWEVER, the compressor will still have liquid refrigerant returning to the compressor; causing rotor lock (and again with the thermal switch in the compressor motor).

In the photo you can see my 15K BTU Coleman Mach III. The "Running Amps" is 11.9 BUT the locked rotor amps is 58 and THAT is at 115 volts.
Yes, if the thermal switch "hangs in there" long enough the 20 amp circuit breaker will open but the compressor should have shut down long before enough heat occurred in the circuit breaker to open it.

As volts go down, AMPS go UP with an inductive motor like a compressor.

5) I have seen cases where that probe has fallen out of the coils (or was never inserted or the coils were extremely dirty from running without a filter) and caused the coils to look like a solid block of ice. The only cure is to let the unit sit OFF for several hours and put a pail under it because there will be water in the camper as the ice melts from the outside, in and the drip pan under the coils will be frozen).

Cleaning the coils on your air conditioners should be a regular maintenance item. AC-Safe Air Conditioner Coil Foaming Cleaner-AC-920 - The Home Depot
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Old 05-27-2015, 07:18 AM   #3
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Lou nailed it!

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Old 05-27-2015, 07:32 AM   #4
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I noticed in one part of that video your door was wide open allowing the a/c unit to suck hot air from the outside to the inside make sure all windows and doors stay shut that will help a lot
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Old 05-27-2015, 07:34 AM   #5
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The best way to check for RV air conditioner proper operation is to measure the difference (AT THE AIR CONDITIONER) between the air going IN and the air coming OUT.

There should be a minimum of 10 degrees of air temperature drop when measured with a thermometer. Your "test" shows the Delta at 20+ degrees so that is awesome.

It sounds like your air conditioner is "working as designed."
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Old 05-27-2015, 07:45 AM   #6
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If your Rv has been shut all day it most likely will take an hour or two to bring it down to a comfortable temperature I've had to set up my 5th wheel in 100 degree weather and it will take a good two hours to bring it down to 80 degrees if I start with an inside temperature of 105
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Old 05-27-2015, 07:46 AM   #7
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Quote:
Originally Posted by iceblaze580 View Post
I noticed in one part of that video your door was wide open allowing the a/c unit to suck hot air from the outside to the inside make sure all windows and doors stay shut that will help a lot
Good Lord! I did not catch that!

That is one good AC to be putting out over 20 degree cooled air with the door open!
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Old 05-27-2015, 07:52 AM   #8
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Yes it is
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Old 05-27-2015, 09:31 AM   #9
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Thanks everyone for the information. (especially Herk) I really appreciate the input.

What started me in "analyzing" the A/C was that a couple of days after we got the camper, i turned the A/C on the night before and set it to 74. It was a cool night (60's) but i knew it was going to be sunny and warm the next day and i wanted to make sure the camper was cool enough as we were going to start stocking it up. Anyway, the next morning, the cab temp was in the 80's. The air coming out was cool, not cold. It was at this point that we noticed the unit would completely cycle off and then 1 second later, would start up again. It sounded like the compressor was starting up with the delay as it should but the air was not COLD coming out, it was cool at best. Sometimes it would come out COLD, but cool more often than not.

Some other info based upon the feedback you guys gave me...

-the temp outside was by far cooler than the inside temperature when the door was open. to the point where if we were actually camping and i didn't have such bad allergies it would have been much better to not run the A/C at all. Humidity has been pretty low. Believe it or not, even the 104 degrees, while hot, was not unbearable. The heat in the trailer had to be just the sun heating up the roof.

-electrically, i put a 30amp outlet outside my house fed with 10 gauge romex. then i have a 25ft CAMCO 30amp extension cord to my trailer. according to my volt meter plugged into an outlet, i get 120 consistently no matter the state of the A/C.

I'm interested in the temp probe issue. (my wife googled our issue and found that as well) Where would i look for the probe? on the roof and take the cover off? or is it inside the camper and take that cover off? The A/C has been off after our tests and i have not had any water inside the camper. does anyone have a pic of what it the probe "should" look like on a DOMETIC unit.

i agree a 20degree delta is good and I've read that elsewhere, but it is not consistent, to the point where i only feel a cooling effect at night. And I'm not sure why the unit completely shuts down and restarts both at night and during the day.

My apologies in advance if you guys feel I'm trying to argue with you, i am not. Just trying to explain in the wake of my frustration. We bought the trailer with a myrtle beach trip planned in july/august and if i can't get the camper cool in may, I'm really afraid of MB!

Dave
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Old 05-27-2015, 12:55 PM   #10
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My 15k A/C couldn't keep up when it was 100 inside and outside in my 37' Wildcat. That was when I decided to installed a second A/C in the bedroom. Now I can cool down the place and then shut one A/C down. Also for the nights we use the bedroom A/C only.
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