Evaporator is freezing over. Figured it was the low pressure switch not shutting off the Compressor. Went to the dealer, talked to service tech. He told me my truck does not have a "low pressure switch", but some other switch which I can not remember right now. Anyways, he told me more then likely it is not that anyway. He told me the AC probe that goes into the Evaporator is the problem ($22 for the part) Has anyone changed one of these? Will the dash need to be pulled to get to the Evaporator and change this probe? If not, how involved is it? Is there a book/manual I could buy on the layout on my AC setup? Thanks for the info guys!!!!

 

Actually, having the evaporator coil freeze over is caused by low freon. Have it topped off and you'll be good to go.

 

This ties into many other threads related to this problem. If you do a search you will find lots of info on this and similar A/C problems.
On my truck I had the problem of the passenger vent sometimes blowing warmer air than the drivers side. Also the A/C would freeze up on the highway, but not in the city. When it did this it got real noisy thru the vents.
I took it in to the dealer recently and they have fixed all my A/C problems under warranty. Have no idea what they did. I don't think it was a low freon problem as just before I took it to the dealer I had an A/C shop put their gauges on it and they could finds nothing wrong with the system.

 

Low charge just SLIGHTLY low (may not be obvious on a gauge set all the time)causes freeze over and poor cooling BEFORE freezing over from pass side vents on these trucks.Also VAPOR coming from drivers side vents.The sensor is a FIN TEMP sensor and its being relocated on 03/04 trucks.Dash has be be removed to do so but its really not a bad job.The NEWER trucks the senor was relocated on a differant part of the evaporator at build time.STAR(tech support) issued a memo on this and which fin/location to move sensor to.Its just advisable at the price of the sensor to install a new one at same time.The FIN TEMP sensor is "the" thermostat.Another recent post on this issue.Dealer tech probably needs to call STAR for new location of sensor if he has not already done one.

 

Have already checked pressure readings, low side was @ 35 LBS of pressure at idle.

I DO sometimes have vapor coming from the vents.

It freeze's (sp?) only crusing at highway speeds (65MPH+), so assuming that that the compressor is spiinning it's fastest @ those speeds, causing it to freeze up. That is why I thought it would be the low pressure switch not shutting the compressor off.

It is NOT making any noise.

And I am not noticing any difference in temps between drivers side and passengers side vent, even though I really can not get a good judge of it since I am sitting in the drivers seat. I DO know that the drivers side vents will FREEZE YOUR BUTT OFF!!!!


So, what you guys are telling me is that it is the Fin Temp Sensor, and it needs to be replaced, AND I need to find out WHERE to relocate it to? Is that correct????

 

YES.BUT as I stated just a HAIR low will cause the vapor etc.I've seen the gauge readings look good on these trucks and evacute it all out and add the PRESCRIBED amount back in and vapor stop and good cooling resume.I run TWO $5.00 ac gauges in mine.One in left vents and one in right vents.When system gets a hair low there is a 6 plus degree differance from side to side.Buy a couple at auto Zone or where not and monitor your temps.

 

I'll go out on a limb here and repeat what was already stated. Low 134A...

 

OK guys, will check again tomorrow. What readings should I get on a day of an outside temp of @ 85*? Last time I checked I was at 35 LBS on the low side at idle. Are you saying i should be @ 40-45 LBS of pressure on the low side? Thanks.

 

When checking the A/C pressures bring the engine up to 1,000rpms.
At 85F the low side should be around 35-38psi and high side not to exceed 325psi at 85F ambient.

MikeyB

 

Will check today, and get back with you guys. HOPEFULLY that is all it is.....

 

OK, went out there a few minutes ago and checked:

90* outside

@ idle 26-28LBS of pressure on low side and @ 220 LBS high side

@ 1000-1200 RPM @ 16-18 LBS on the low side and @ 245-250 high side



So, definitely low. Going to add some freon tomorrow. My only question however is at this point, WHY is it freezing over when it is LOW on freon? I have always been under the impression that when it is low on Freon, it will not cool. This thing will FREEZE your butt off until the Evaporator freezes over. How is that possible when it is low on refridgerant?

 

Higher pressure keeps the freon from dropping below the point of freezing. As the pressure drops so does the freezing point. And if the pressure gets too low no cooling at all, since the pressure switch will keep the compressor clutch from engaging.

MikeyB

 

I've done some work on automobile systems, but mainly on residential and commercial units. People always question why their evap coil will be frozen when I'd tell them the system is low on freon. The only other things that'd cause a similar situation are a very dirty condenser coil or filter in the air handler.
Now as to why your system is low on juice.....? An old timer once told me to turn the air on once and awhile during the winter after the engine is up to temp. This, supposedly, would lubricate seals in the system.

 

Well, since adding freon is the chepest alternative at this point, and from what you guys are saying, makes since, I will start with that. And hopefully that will take care of my problem. ONce I add the freon, I will post an update and let you guys know what the out come is, so stay tuned.....

 

From what I remember when I used to be a tech the low side should be between 24 to 28 PSI min at 1200 to 1500 rpm. High side should be between 200 and 250. Never seen a R134a system get over 280 PSI on the high side. Word of wisdom. The number of A/C failures on a auto A/C unit is very low. The reason is the Compressor runs even when you have the heat on. Not long but it will run. Keeps the system lubed up. Prevents the seals from hardening. I run my A/C alot. My wife threatens me everytime we go on a trip. I usaually keep a jacket for her in the back. Hot natured I guess. Don't do the role down the window thing. Can't stand the noise. I will crack it but that is it.