AC evaporator coil freezing up

[dsmith3]

Good afternoon -

First-time RV owners... We have a 2015 Jayco JayFlight 32BHDS that we took delivery on in December. It has two Coleman Mach rooftop AC units (15K BTU main ducted unit with wall-mounted thermostat and a 13.5K BTU unit in front bedroom with controls in shroud at ceiling integrated with unit). We've camped several times using AC with no problems.

Last weekend I was running only the main 15K ducted unit and it ran most of the afternoon and night. The next morning no air was coming out of ducts. Upon inspection I found that my evaporator coil had iced up. We shut it down and just ran the 13.5K front unit Sat and Sunday. Both evap and condenser coils are pristine (as you would expect on new trailer).

Could this just be normal reaction to user (me) violating "best RV AC practices"? We had thermostat set pretty low (65-70) and nighttime temps outside got down into the 60s. Fan was on Auto and unit ran pretty much constantly. From all I've read online since we got back it sounds like I should have had thermostat set higher (ex. 78) and had fan set to "On" (instead of Auto) and "High".

Appreciate any tips and advice.

[dsmith3]

JohnG3 wrote:
The compressor should have cycled with the fan. If it didn't the unit worked like a refrigerator. Try again with the fan on all the time like you thought. If it ices up again make sure the filter is clean (I know new RV but still, it's happened), and there are no obstructions to the air going into and out of the unit. Our AC unit has a sliding grate on the discharge side that allows all the air to go into the living room or close it and the air goes through the ducts to the bedroom and front of the RV. If there is a blockage (vents closed in other parts of the RV for instance) that would limit the air flow and cause icing.

Good luck.

Thanks, John. Filter is perfectly clean. Also, when we had the "no air" issue, no air came out of the "dump vents" under the main unit when I opened them. I don't think I've got a blockage in ducts. Main question is how to prevent the evap coil from icing up.

[dsmith3]

Thanks, Fred. I'd like to check temp of air coming out of vents but don't have access to 30-amp pedestal (trailer is in front of our house at the moment about to be towed back to storage unit). But I do have two Honda 2000 gens that I should be able to use to fire up the one problem 15K AC unit. Any problems with this idea?

[JohnG3]

The compressor should have cycled with the fan. If it didn't the unit worked like a refrigerator. Try again with the fan on all the time like you thought. If it ices up again make sure the filter is clean (I know new RV but still, it's happened), and there are no obstructions to the air going into and out of the unit. Our AC unit has a sliding grate on the discharge side that allows all the air to go into the living room or close it and the air goes through the ducts to the bedroom and front of the RV. If there is a blockage (vents closed in other parts of the RV for instance) that would limit the air flow and cause icing.

Good luck.

[Golden_HVAC]

Yes you are right, leaving it at 78, and it probably would not freeze up, because the coil temp will stay above 45F.

Leaving the fan in 'on' would have also thawed out any frost on the coil during any compressor 'off' time. However if the thermostat was set cold enough, and there was no off time, then the coil can still freeze.

Check your air temp output. You might have a freon leak, and it is best to change the A/C while the unit is new as possible. Then you will still have 5 more months to test the replacement unit, under warranty if required. Don't think they only have a 6 month lifespan, my 1997 unit is the factory one, so they do last a long time.

So if air in is 85F, then air out should be between 18 and 22F cooler. So 63 - 68F would be acceptable. I am suspecting that your air is not coming out very cold, and as a result the compressor rarely shuts off, and that caused it to freeze. (because the compressor ran so many hours without freezing you out).

Lets say that the rear A/C is getting the air cooler by 22F, and the front one only cools the air by 12F. This means that the back one is working great, and the front one will take more than 10 hours to cool that area, good thing you have the second one! And with less than 15F temp cooling, they need to replace the front one under warranty, unless they can find the leak and repair it.

I did repair a leaking rooftop RV A/C once for a friend. It took me about 4 hours, and the leak was right there, easy to repair and install the fittings, and then evacuate, and recharge it. If my work had billed for my time, the estimate would have been something like $725. That is $150 an hour X4 and $62 in materials X2.

Good luck!

Fred.