Air Conditioner ice up

[dschultz]

I am having problems with my A/C in my 2002 3500.

If I drive for several hours with the A/C on the lower fan speeds the evaporator coil ices up and airflow is reduced. Shutting off the compressor until the ice melts allows the airflow to return.

The cabin air filters have been replaced.

The truck is at the dealer now, but service guy says he can't duplicate the problem. (duh!)

The system also seems weak when temps are above 85 degrees. ( I need to use recirc all the time adove 85 )

The system ices up when on fresh air only.

I thought there was a temperature or pressure switch to prevent the ice up.


Any Ideas?

Dave

[ram/tx]

dschultz--I made two trips to West Virginia in mine and both times the AC froze up on me in the high humidity you'll have up there. It doesn't seem to do it down here in Texas where the humidity is not as high as your's is. Don't know if this has anything to do with it. I know some of the others guys on here have had the same problem, but I don't think anyone has come up with a fix for it.

[ChevysRus]

Ice up is due to high humidity getting into the airflow circulating over the Evaporator coil. Couple of causes are using Fresh Air or having windows cracked or down a little sucking in high humidity. Best to use Recirculate when in high humidity as air is already "somewhat dry" from first pass over coils.

You can also run the fan a little lower speed to reduce the amount of airflow over the coil and give the humidity a chance to evaporate before it piles up on the coil. High fan speed circulates more air over the coil and if high humidity... well you get the picture. Kind of defeats the purpose of quickly cooling off the truck, but when you are in a hot and high humidity situation, there are tradeoffs as no system mobile or commercial can keep up with Hot high humidity. Funny that rain is not usually an issue as ambient air temps are lower.

If you are not getting cold air, then could be partial icing and not enough to shut down, but enough to effect performance. These trucks have a high capacity A/C system and normally mine will freeze me out and I have to turn fan down low or move vents so they don't blow directly on me or worse case turn the heat/cold temp switch back up a little.

Good Luck, try the recirculate and low fan speed, will take a little longer to cool, but should not ice up and shut down completely.

[Lone Eagle]

This one is easy. The low pressure switch is bad. They should not ice no matter where you live or what the humidity. Later! Lone Eagle ;)

[Tommy turbo]

Correct.Low pressure switch is not cycling the
compressor when it needs to per low side pressure.

[AbqGeorge]

Are you sure about the "slow speed" thing chevysRus?

My experience has been that running the fan full bore resulted in less icing problems? Of course, my experience base is mostly with this dry desert southwest?

[TBC]

Turn the temp down slightly in high humidity. This has happened in every GM vehicle I have ever owned including my 2001. I turn the temp down very slightly and no problem and it stays cool. Running on recirulate does help.

Low freon will also cause icing. This is true in house or auto or RV a/c units.

Tom

[a64pilot]

Low freon will also cause icing. This is true in house or auto or RV a/c units.

Tom
I'll second this as the probable cause

[dschultz]

I got my truck back from the dealer tonight.

They replaced the low pressure switch.

A long trip will tell if the icing problem is solved.

The A/C also seems to work a little better now, It might have been a little low from the factory.

Thanks for the help!

[cmtndmax]

My 02 iced up monday after about 2 hrs. of using recirc & slow fan speed turned to outside air and no more icing. My 94 worked the same. I could not leave it on recirc without icing.