AC evaporator coil freezing up

[dsmith3]

Good afternoon -

First-time RV owners... We have a 2015 Jay Flight 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.

[Grumpy]

If it is humid, running the fan on low will cause icing problems. I always run ours on high unless we are just using it to circulate the air then I will use low. The cooler outside temps probably just enhanced the problem.

[herewego]

Low on Charge .......................

[Grumpy]

Originally Posted by herewego

Low on Charge .......................

Right from the owner's manual:

II. Operation During Cooler Nights (Cooling

Operation).
It is important, when the outdoor temperature drops in the
evening or during the night to below 75 degrees F., that the
thermostat (temperature control) be set at a midpoint between
“Warmer” and “Cooler”. If the setting is at “Cooler”, the
evaporator coil may become iced-up and stop cooling. During
the day when the temperatures have risen above 75 degrees F.,
reset the thermostat switch to the desired setting.
NOTE
Should icing-up occur, it is necessary to let the cooling
(evaporator) coil defrost before normal cooling operation is
resumed. During this time, operate the unit in the “HIGH
FAN” position with the system at maximum air flow. When
increased or full air flow is observed, the cooling coil should
be clear of ice.

[dsmith3]

Thank you, Grumpy. This sounds like exactly what occurred in our situation (ran the AC at low setting at night with outside temps dipping down to the 60s).

I will know better now.

[tugboat95]

Don't know exactly why but this is exactly the same thing that happened to us last time out. Ran it on low with temps in the low 70's and it froze up. Worked great in the daytime but froze up every night. Thought I had a low charge. Might exam this scenario a little more before I spend some money.

[VicS1950]

Originally Posted by tugboat95

... Might exam this scenario a little more before I spend some money.

It sounds more like it is operating conditions, not low charge.

Jayco gives the proper operating settings, but from what I saw doesn't mention why.

Comfort cooling is a combination of lowering the room temperature and de-humidification. If the temperature is lowered too quickly without removing moisture from the air then the space can feel cool, but clammy and uncomfortable.

The humidity is lowered (moisture removed) by the water in the air condensing on the evaporator coils to trickle down, collect in a pan, and then is sent to a drain. That is why you get a stream of water out of an operating air conditioning unit. As an example, you will get more water out of an operating A/C unit in humid Florida than you will in dry Arizona areas.

The air flow over the evaporator coil is critical to keep the coil temperature from getting too low. If the air flow doesn't keep the coil from getting below freezing then the moisture in the air will cause frost to build up on the coil rather than trickling down and out to the drain. As more frost builds up it further blocks the air flow which sets up a deteriorating condition. That causes the evaporator coil to "freeze up" or get covered with ice. Once covered in ice there is no air flow, the room temperature stays high because the air flow is blocked, the thermostat is never satisfied, the A/C unit runs full out without cooling the room, and evaporator coil becomes an ice maker.

Night operating with low load on the A/C system, low ambient temperatures, and low fan speeds sets up conditions which can cause coils to freeze up. A dirty air filter will also restrict air flow and can contribute to the problem.

Keeping the air filter clean and setting the controls at night as Jayco suggests should avoid your problems.

FWIW. vic

[dsmith3]

In addition to running at night with thermostat set too low, I found that my freeze control sensor was disconnected from the evap coil when I removed AC shroud. See loose white wire in attached photo. Will definitely need to place that back between the fins in the coil.

[Socco1]

Rule of thumb we have in the Commercial A/C business... If you set your cooling setpoint lower than 68ºF, the evaporator will begin to ice up.

[mike837go]

Please pardon my ignorance, but why is an modern A/C unit designed to allow the evaporator coils to drop below freezing (0*C)?


We're dealing with human comfort, not keeping the ice cream solid.

[VicS1950]

Originally Posted by mike837go

Please pardon my ignorance, but why is an modern A/C unit designed to allow the evaporator coils to drop below freezing (0*C)?

...

Cost.

Fancy controls are expensive.

vic

[Jopopsy]

Last night we got back from Epcot to find the coach was 76 inside. We did not have the AC on. I put the AC on and noticed shortly after my condenser would cycle even though the fan kept going. Fan is on Auto - t-stat was on 72. Outside air must've been around 65 or less. Maybe 62?

I'm hoping it was my frost sensor keeping the system from becoming an ice block. Heat pump function seems to work fine. Going to try again in a couple hours when it warms up around here.

[Dustdevil]

Originally Posted by dsmith3

In addition to running at night with thermostat set too low, I found that my freeze control sensor was disconnected from the evap coil when I removed AC shroud. See loose white wire in attached photo. Will definitely need to place that back between the fins in the coil.

This is what I experienced. The sensor was on a friction clip that attaches to one of the tubes on the coil. It would corrode from the moisture, and make very poor contact. All i had to do was pull it off and scrape off the corrosion, replace it on the tube, and it worked like a champ.

Originally Posted by mike837go

Please pardon my ignorance, but why is an modern A/C unit designed to allow the evaporator coils to drop below freezing (0*C)?
We're dealing with human comfort, not keeping the ice cream solid.

They do actually have a sensor. It's what tells teh compressor to stop sending refrigerant through the system. But if its not working properly for whatever reason, you get freeze up.

[Jopopsy]

Investigating further I took off the bottom plate and plastic divider on my Coleman. There is a thick wedge insulation/divider that separates the supply and return. Mine was not seated properly - so I wedged it so it sits in the track of the plastic divider and it now makes a firm seal with the top and bottom of the plate and AC unit.

So far so good - and I haven't felt cold air come out of this thing like this in a long time. If ever.

[pconroy]

Originally Posted by Jopopsy

Investigating further I took off the bottom plate and plastic divider on my Coleman. There is a thick wedge insulation/divider that separates the supply and return. Mine was not seated properly - so I wedged it so it sits in the track of the plastic divider and it now makes a firm seal with the top and bottom of the plate and AC unit.

So far so good - and I haven't felt cold air come out of this thing like this in a long time. If ever.

That sounds like what's going on in ours - Jayco had wedged a rectangular piece of insulation that also forced air into the ducts.

It came loose, I re-wedged it - twice.
Then twice with duct tape - didn't hold.

Finally, into the woodshop with some scrap 1/4" ply to make a wedge for the wedge and it seems to be holding. Hope you have a better experience!

[Rock]

X2 on the big piece of separating insulation just laying there on my bedroom ac Reinstalled with ac silver tape and all good. Talked with Jayco about why they do not taped it in. They now are after complaints.

How is the main quiet unit separated since there is no inside piece. Has anyone pulled that unit from the roof? I should of asked Jayco that
Rock

[2naEagle]

Jopopsy, pconroy, Rock. Same here separating insulation on bedroom unit was out. It had been Wedged in place with one little piece of tape. Had to retape it. It is just a absolute shame this happens. I do not like not being able to see the living room unit.

I did get on the roof and checked living room unit. Had to pull off covers to see inside. It looked ok. I did add some tape but it was very hard to get to without removing the whole A/C. Just did the best I could.

[Rock]

Thanks for the reply. I am gonna pull my cover next time on roof and check it out. I bet it is hard to get to in place. When I get my roof redone I will ensure it gets a good tape job.
Rock

[Jopopsy]

Originally Posted by Jopopsy

Investigating further I took off the bottom plate and plastic divider on my Coleman. There is a thick wedge insulation/divider that separates the supply and return. Mine was not seated properly - so I wedged it so it sits in the track of the plastic divider and it now makes a firm seal with the top and bottom of the plate and AC unit.

So far so good - and I haven't felt cold air come out of this thing like this in a long time. If ever.

So I'm camping again and I have the same problem again. I also have the same solution. So I suppose my wedge/divider is coming unseated/loose as I'm underway.

Looks like I need to get some aluminum tape and get to work up there fastening the wedge in more permanently. Seems like a poor design for an appliance w/ such a great track record for reliability.

[Rock]

Originally Posted by Jopopsy

So I'm camping again and I have the same problem again. I also have the same solution. So I suppose my wedge/divider is coming unseated/loose as I'm underway.

Looks like I need to get some aluminum tape andm get to work up there fastening the wedge in more permanently. Seems like a poor design for an appliance w/ such a great track record for reliability.

At least that is an easy fix on the bedroom unit. Also make sure the sensor temp wire end is in the evap coil. I put a dab or silicone on mine to ensure it does not com loose.
The low profile units have two separate fans unlike the tall units
Rock