RV AC icing

[MarkB_MI]

During a recent trip, I discovered the evaporator of the Dometic air conditioner on our fifth wheel will ice up after several hours. Eventually the airflow is blocked; running fan only for a few minutes will thaw it out and then it will be fine for a few more hours. This AC is only about a year old; the original unit, only two years old, was replaced under our maintenance contract when it failed last year.

Is this a common problem with RV air conditioners? Or is it likely our unit has a leak and will fail soon?

 

[Steve@Advance]

No, not normal.

Probably low refrigerant.

Not likely restricted air flow as new as it is.

Is it still under warranty? They may extend the warranty, as that is not acceptable unless it was damaged.

 

[K-Mo]

I'm not a professional, just a shad tree opinion.
High humidity and cold coils = ice.
I would think the AC unit would have a thermal sensor to prevent icing.
Perhaps a knowledgeable AC person will tune in for a more professional answer.

 

[caterpillar guy]

I was always told to set the fan on high then the temp as warm as was comfortable this way the coils didn't freeze. May have been on old wives tale. I do know I have never had a problem with them freezing up that way.

 

[marloweg]

ours did that if we tried to make it to cold inside the RV

 

[John T]

Good question "Is this a common problem with RV air conditioners?"

NOT in my experience with 49 years of RV ownership, but that don't mean it cant happen, it was just NOT common with the many many Ive owned

John T

 

[Texasmark1]

Low freon could/can be a source. Problem is, why do you need freon at this age? Assuming it worked ok for you up until this current problem....sounds like leak to me....maybe vibration from being what/where it is cracked a braze joint somewhere....my 2c.

 

[MarkB_MI]

> Is it still under warranty? They may extend the warranty, as that is not acceptable unless it was damaged.

Well, we bought a seven year maintenance contract, so we should be able to get it replaced a second time.

 

[Texasmark1]

Funny, I just got up to refill my coffee cup and asked myself, why would low freon cause an icing problem when you would think low freon wouldn't be cooling as well.....well my simple mind came up with this answer:

The Expansion Valve, regulating the flow of freon, senses the temperature at the outlet of the evaporator. It adjusts the opening in the valve to keep the outlet just above freezing when operating normally. With low freon levels running through the line the valve thinks that the evaporator is too hot and opens wider to allow more freon resulting in an overcool condition....for the amount of air flowing across the evaporator at the time and temp. Just a thought.

 

[DoubleR]

I'm sitting in my 16 year old 5th wheel now air conditioner has never give me a problem it's been running here all week where I'm at. I'm hoping to upgrade soon hopefully it'll hold out till then.

 

[MarkB_MI]

> sounds like leak to me....maybe vibration from being what/where it is cracked a braze joint somewhere

Yeah, that's what I think. Very possibly that's what killed the first unit as well. There are plenty of reviews on Amazon for this particular unit (Brisk II) where they failed within the first two years.

 

[MarkB_MI]

> I was always told to set the fan on high then the temp as warm as was comfortable this way the coils didn't freeze. May have been on old wives tale. I do know I have never had a problem with them freezing up that way.

Yes, that's what I've been doing and it seems to help. I don't think it should be necessary, though.

 

[Tony in SD]

Air flow is sometimes a cause although I never had an RV AC freeze up on me. But I have taken several bird nests out this year. For some reason the birds have been attracted to every opening in my RV this year.

 

[sotxbill]

several things can cause that...

low on Freon

running fan on low in a very high humidity area

stopped up drains on the evap coil.

expansion valve stuck wide open on a variable expansion valve

blocked air flow on coil or dirty filters

 

[Metal Man]

Is this the first you have used it sense it was replaced or have you been using it and now
it has started icing up. My point is maybe it wasn't charged enough at first or then it is a leak.
Have you checked the air filter in the air handler. A plugged filter will reduce air flow
causing pressure drop in coil and causing it to freeze up. Hope this helps.

 

[Tractorman90]

Our camper did this all the time. We didn't have AC in the house, but dad would leave the camper plugged in so us kids could go out and sleep in there when it got too hot out. Those camper ones were not very advanced, and had knobs like a car from the 90's. One knob controlled fan speed, and the other the "temperature". There was no auto mode or temperature sensing. Being kids, we would just turn the fan on high, and the temp all the way cold. During the night, the temperature would drop and the humidity would go way up. By the morning, the AC unit was froze over. We would then turn the temperature to high with the fan on, and it would defrost back out, just like you did. It was always ready for the next time we needed it. There was never anything wrong with it.

Since ours was a simple AC unit, the temperature knob controls how much pressure is in the system, which is a poor man's way to control cooling amount. It was all mechanical and simple circuits, so it had no ice prevention. On systems with an electronic controller, they will have a temperature sensor comparing the temperature entering the unit and determine how often the compressor needs to be turned on. That's how almost all window AC units available today work. If your unit is a simple knob-controlled one like ours, then you're fine and just need to turn the temp down a bit. If it's an electronically controlled one, then you may have leakage or the temperature sensor is faulty.

 

[High Octane]

My rv is 1986
Have to wash out every year sometimes two three times thru summer. Bugs, leaves, get in there.

 

[buickanddeere]

Fan on high ?
Nothing anywhere that could be instructing evaporator airflow ?
Somebody have a window or door open for fresh air ? Or running AC in the daytime and opening the windows at night which lets the humidity back in .
Fan on continuous instead of Auto ?

 

[MarkB_MI]

Thanks everyone for your suggestions. I think I found the culprit. After checking for refrigerant leaks with my leak detector, I decided to try RTFM. In the installation instructions, I found this step:

Insert the freeze control sensor into the
evaporator coil fins approximately 1" above
the bottom of the coil fins and on the left side.
See (FIG. 17). Bend fins over sensor to se-
cure in place.

I was a bit suspicious that this sensor was just loose in the air return, but I didn't see an obvious place to put it. Now, I see the hole in the evaporator fins where it must have been originally stuck (not in the right place) and probably fell out of. I stuck the sensor where it's supposed to go and I'm testing now.

 

[Donaldinky]

Just a guess check thermostat. See if it's not shutting it down. Causing it to get to cold. Or bad valve in compressor. Seen reversing valve. On heat pumt do that.

 

[c.oawright]

(quoted from post at 09:15:22 08/25/20) Funny, I just got up to refill my coffee cup and asked myself, why would low freon cause an icing problem when you would think low freon wouldn't be cooling as well.....well my simple mind came up with this answer:

The Expansion Valve, regulating the flow of freon, senses the temperature at the outlet of the evaporator. It adjusts the opening in the valve to keep the outlet just above freezing when operating normally. With low freon levels running through the line the valve thinks that the evaporator is too hot and opens wider to allow more freon resulting in an overcool condition....for the amount of air flowing across the evaporator at the time and temp. Just a thought.

Yes... Low freon ,Expansion valve or low side pressure switch bad.

 

[Blackhole49]

Not sure about this. My 91 Dutchman I bought new has a fan and temperature control knob on the original Coleman AC. The temp knob is just that. It causes the compressor to cycle on and off when the desired setting is reached while the fan (high/low) runs all the time. On my unit the fan control knob has 4 settings: Low Fan, High Fan, Low Cool, High Cool. This 29 year old worked perfectly running for 72 straight hours at the Silver Lake Sand Dunes last week. When it cooled off at night, just the fan ran.

 

[MarkB_MI]

OK, so it's run over a day since I jammed the freeze sensor into the evaporator fins, and NO ICE! It looks like the problem is solved. Thanks again, everyone.