Air Conditioner Freezes Up

[orgtech]

Having problems with my AC. When under load like pulling my trailer the AC tends to freeze up. Did it 5 or 5 times last week. Turned it off for a while and it thaws and works again. Doesn't seem to freeze up using it around town with no load. The problems been around a long time. Had the freon checked a few years ago when it happened then and was ok. Just started towing again and need to get to the bottom of this. Any ideas would be appreciated. Thanks

 

[Got HO?]

Probably slightly undercharged. Mine would do that if it was slightly low on refrigerant. Try adding a couple of oz.

 

[RVTRKN]

Low pressure safety may not be opening above 30 psi. 27. 8 psi is at freezing for 134a, any time pressure drops below that ice will start to form.

 

[RDeFayette]

Mine did the same thing.

Is it especially problematic when the humidty is higher?

Had the thermocouple in the evaporator replaced and took care of the problem.

 

[Cosmo]

Thermistor would be my guess as well.

 

[DZink24]

i had a friend that is a commercial HVACR tech recharge my system. works 100% better now. .

 

[Kry226]

There was a TSB for this model way back and I believe involved moving the fin sensor inside the HVAC box in the dash to prevent freezing.

 

[JJPage]

Having problems with my AC. When under load like pulling my trailer the AC tends to freeze up. Did it 5 or 5 times last week. Turned it off for a while and it thaws and works again. Doesn't seem to freeze up using it around town with no load. The problems been around a long time. Had the freon checked a few years ago when it happened then and was ok. Just started towing again and need to get to the bottom of this. Any ideas would be appreciated. Thanks

Two things, the first issue of freezing the coil is most likely low charge, even though the pressures are "within" spec. Add a 12 oz can of 134A(without sealant if you can find, I use the sealant) and your situation will probably disappear.



The second reason is, around town the evaporator drains much better. I do not know if you have noticed, but after using the AC on the hiway, then coming to a stop, the condensate pours out of the discharge drain on the firewall. That is why it freezes easier at hiway speeds, more water/condensate available at the coil. It was discussed many years back, that placing a 90* elbow(pointed down) on the condensate discharge line, on the passenger side firewall would help in the draining at hiway speeds.



I went to NAPA and purchased a little 5" long rubber 90* elbow, slid it over the discharge line and done. It has helped somewhat, but the largest advantage came from the extra refrigerant. I cannot help but wonder if actually building a "trap", instead of just the elbow, would not be more beneficial. This is what is done on residential and commercial units to overcome the vacuum, and allow the condensate to drain properly.



Jess



Here's a pic of the elbow, top center

 

[orgtech]

Thanks guys, I have a few good ideas to look into.

 

[MFalkinham]

There was a TSB for this model way back and I believe involved moving the fin sensor inside the HVAC box in the dash to prevent freezing.

I agree. My '03 A/C also freezes up like orgtech's truck does. I've already purchased the replacement fin sensor but have not yet installed it.

My understanding is that the sensor can be accessed replaced by either cutting a hole in the HVAC airbox, or possibly by removing the blower motor, or else by pulling the left side of the dashboard away from the firewall. I haven't decided which of these methods to try first.

Here is a link showing where the sensor should be relocated to on the evaporator... ... .

https://www.turbodieselregister.com...-Relocation-WHERE&highlight=evaporator+sensor