AC is icing up but not cooling

I'd get a new one instead of spending a grand on the old one.

Make sure the fan is set to high speed. If it`s not the evaporator coil might be freezing up.

For icing up:

Assuming you have a wall thermostat you should have a freeze sensor that needs to be right up on the evaporator. These are notorious for falling away due to poor installation.

Secondly while you have removed all the interior trim to find the freeze sensor, check that the divider that separates the air in and air out plenum is well placed and sealed to prevent recirculating of chilled air.

But I find it odd you say it is iced up and the tech says a needs a new unit. Are you sure it is iced up? Usually they will blow cold air for at least 20 minutes before the ice interferes with cooling.

smkettner wrote:
For icing up:

Assuming you have a wall thermostat you should have a freeze sensor that needs to be right up on the evaporator. These are notorious for falling away due to poor installation.

Secondly while you have removed all the interior trim to find the freeze sensor, check that the divider that separates the air in and air out plenum is well placed and sealed to prevent recirculating of chilled air.

But I find it odd you say it is iced up and the tech says a needs a new unit. Are you sure it is iced up? Usually they will blow cold air for at least 20 minutes before the ice interferes with cooling.

Pay attention to this reply.....all good advice especially about the freeze sensor :-)

My poor old Dodge 2500 has a bad freeze sensor but it's located deep under the dashboard, impossible to get to without 5 hrs of labor.

So when its humid out and the coil freezes over we just shut the AC off and in a few minutes all is well again when the ice melts :-\

Ron W.

Freeze up is generally 1 of 3 things:
1. Freeze sensor not located properly
2. Coil dirty and or diminished air flow or air leak . . . Go on roof remove cover. Remove evaporator cover . . .
Clean coil
3. Low refrigerant.

Not a bad reply in the bunch!

Here's the Text Only of Chris Bryant's A/C Tuneup Thread. It's been moved around so much that the links to the pictures don't work right.

I was able to find the Diagram Chris drew and refers to:



Front of RV is on the LEFT in the Diagram. You need to remove the decorative cover then enough internal shrouding to access the Blue Indoor Coil, properly called Evaporator. The Red Outdoor Coil, the Condenser, should already have decent access, once the Cover is off.

Chris had a pic of Freeze Sensor, which I can't find, but it's on the forward side of that Blue Coil.

I plan to clean our Coleman Mach 15 today and I'll get a couple pix. It's straight cool and non-ducted so no Freeze Sensor or Reversing Valve.

When it's dirty, the Evaporator Coil is now insulated, and water that should drip off, Freezes. If Refrigerant charge is low, then the reduced amount expands right at the Evaporator Inlet. That overcools the one area, enough that condensate freezes. The frozen area expands because the ice is an insulator and prevents air flow across itself.

But please heed Chris' words: Not Usually Low Refrigerant!

If lines are icing, compressor is running and there's at least some refrigerant. I suppose the Reversing Valve that switches unit from Cool to Heat could be in trouble but let's not jump to that conclusion.

See if you can inspect both coils, clean as needed, and get back to us. Just remember, BOTH, not just the Condenser you can see in back right away.

Icing is caused by one of two things. Reduced air flow due to use of LOW speed and clogged filters.. But from the sounds of it this is NOT your problem for you have cleaned the filters.

Low refrigerant. I have seen ONE TIME it was not low refrigerant in my life... Several where it was.. This indicates a leak in the supposed to be sealed system so you will need professional help if this is the cause.

My off-road POPUP trailer setup will do this especially when running all night long at an electric camp site when it is very humid outside...

I seem to help things by making sure I have a portable fan running inside the trailer...

In my case being a POPUP I'm sure it has something to do with my fabric walls and plastic covered windows not insulated enough from the outside...

Just something else to watch for on those very humid nights...

Roy Ken

OP said the lines are icing up0. Lot of folks addressed the evaporator.

Exactly what is the symptom? Where is the frost?

You can turn the heat pump mode on for a few minutes to dry out the condenser. Florida is full of humidity and sometimes I have to do that on one of mine. I do keep the condenser very clean. I have replaced the sensor as well.