AC evaporator coil freezing up

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.

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, 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 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.

This always happened to my 13,5000BTU air conditioner when it was very humid at night...

Never did any damage but was a nuisance. Had to run fans only to melt the ice the next morning... It did help sometimes by running a couple of fans inside during those nights.

Roy Ken

RoyB wrote:
This always happened to my 13,5000BTU air conditioner when it was very humid at night...

Never did any damage but was a nuisance. Had to run fans only to melt the ice the next morning... It did help sometimes by running a couple of fans inside during those nights.

Roy Ken

Thanks, Roy. Glad to hear it can be a somewhat normal (albeit inconvenient) issue. Definitely two oscillating fans on our our list for next Wal-Mart trip.

Don't these have a freeze sensor like Dometic?
If so it is fairly common for the sensor to be placed improperly to control the freezing issue.

http://www.rvcomfort.com/pdf_documents/1976342.pdf See p10

Most manufactures state somewhere in the owners manual that if in high humidity conditions to run the fan on high not low. If there is not enough air flow over the coil they can freeze up. Check your manual.

Freezing of the evaporator (Cold) coil happens for one of several reasons.

I list the most common ones in no particular order

1: Reduced/impaired air flow.. Some say just running the blower/fan on high is enough to prevent it..By all means clean the intake filters

2: LOW Coolant,, The "Freon" (not really any more) used if low can cause freeze up.. IF it's leaking coolant replacement may be in order

3: Many RV air conditioners have a frost sensor.. This is a probe stuck in the bottom of the evaporator.... If it is lying in the drip tray it does not work.

Very high humidity and dirt can combine to cause all sorts of problems.

Your MAIN AC HAS a freeze sensor and will NEVER freeze up if it is installed and operating correctly. Your Bedroom AC does NOT have a freeze control. You need the unit checked out. It is under warranty. Doug