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.

[dougrainer]

wa8yxm wrote:

dougrainer wrote:
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

Mine does. (Have a sensor)

What part of this post is your comment directed at?????? IF you have a sensor and the unit freezes up the sensor is defective. Doug

[wa8yxm]

dougrainer wrote:
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

Mine does. (Have a sensor)

[dsmith3]

Removed AC shroud and, behold... what greeted me was a white wire dangling down from panel labeled "FREEZE". Lotta smart folks on this site. Appreciate y'all.

[dsmith3]

Thanks. Will check out the freeze control sensor.

[Dave_H_M]

ds, listen to the folks talking about the freeze sensor.

In a previous fifth wheel, it had fallen out of the evaporator and that caused freeze ups.

Check on the simple things before you progress to the theoretical things.

you may be able to find a youtube on it?

[dougrainer]

dsmith3 wrote:
Thanks to everyone for their contributions. In addition, here's an applicable blurb from owner's manual I found online...

OPERATION DURING COOLER NIGHTS
It is important, when the outdoor temperature drops in the evening or during the night to below 75°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°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.

Congratulations on finding a owners manual and reading it, but as with some things in life, it does NOT apply to your specific situation. THAT note is for your front bedroom AC with mechanical controls. The problem is your freeze sensor control. Doug

[time2roll]

That manual seems to be for the ceiling unit without a wall thermostat.

Run the 15k unit and the freeze sensor should keep the compressor cycling and keep you in cool dry air.

[dsmith3]

Thanks to everyone for their contributions. In addition, here's an applicable blurb from owner's manual I found online...

OPERATION DURING COOLER NIGHTS
It is important, when the outdoor temperature drops in the evening or during the night to below 75°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°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.

[dougrainer]

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

[wa8yxm]

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.

[fpresto]

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.

[time2roll]

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

[dsmith3]

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.

[RoyB]

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