Lowco

A/C will work perfectly for 20-30 minutes, then you notice less and less cool air being put out the vents. Seems like the coil under the dash is freezing up not allowing the air to pass through! Turning off the A/C button for 10 minutes or so seems to thaw it out and you start getting airflow back out the vents, then you can push the A/C button for cool air again!

ANYONE Experience this or know the fix for it?

tcr

I just this weekend had this pop up, it is your evaporator coil freezing, the low pressure switch should prevent this.

billyrae

Is Texas humid?

Lowco

Some parts in the south are VERY humid.
Here where I'm at it is not.

rico334

tcr-
Pardon my ignorance here, but what exactly is the low pressure switch you are referring to? Thanks, Rick

MikeyB

If the system is low on freon the evaporator can freeze up.

MikeyB

handymantim

My first thought was the same as MikeyB's. Check your R-134a pressures. You can buy a can at Wal Mart that has a pressure guage already on it with red and green shaded areas. It's not exact but if you'd rather spend your money on something else then go for it.

CRXsi

An evaporator freezing up can indeed do this but usually this is a result of overcharging as too much R134a enters the evaporator, like wise you could also have a faulty expansion valve again causing too much refrigerant to enter the evaporator and the result is icing up (too much cooling to the point that all condesation on the evaporator fins turn to ice instead of dripping onto the pavement via the drain tube). The other thing you should check is to be sure your evaporator drain tube is not plugged (make sure that while the AC is running that you get some water dripping out the passenger side onto the ground) because if the drain tube is either plugged up or not connected properly this will cause the water to not drain out of the evaporator properly and instead can ice up on the evaporator. (sometimes this shows up as damp or wet passenger floor mats). I personally would NOT add any R134a from walmart and would instead take it to an AC shop or the dealer to have them check the pressures or determine how many lbs of R134a are in the system. If the system is overcharged then adding more will only make it worse. The low pressure switch is a switch that if the pressure on the low side of the system becomes to low (ie excessively low on charge) the the AC compressor will not turn on. Checking pressures can be relatively accurate but sometimes it is just as easy to recover and evacuate the system so that you can see how much was taken out of the system. This can tell you if you are even slighty under or overcharged. (ie. system holds 1.5lbs, 1.65 recovered = system overcharged)

How many miles on your truck? Have you had any recent AC work? If you are in warranty why not just go to the dealer? The only way a dealer can make you pay under warranty for ac work is if a rock has damaged your condensor. Otherwise any other problem should be covered under warranty (assuming you are still in basic warranty).

For a decent description of how the automotive ac system works visit:

http://www.musclecarclub.com/library...itioning.shtml

kertoncol

I had this happen. They changed out the control head (switch, temp selector, etc.) but that didn't help. They then changed out the door for the selector, that didn't help either. They then put dye in the system and recharged the freon. Later they checked but didn't find any leaks. So far it's been fine. They claim that the system was freezing up because of the low freon. Hope this helps.

tcr

A low pressure s/w not only tells you the 134A level could be low, it also cycles your compressor if you use your fan on low(poor airflow causes low suction psi).
Also a dirty evap coil will cause low suction psi(tripping the LPS), A low outdoor ambient combined w/ low airflow also causes the LPS to trip more often. The old dodges had a temp sensor on top of the evaporator that would cycle the comp if the air/coil was too cold, along w/a LPS. I have not torn into the new systems yet, but I will and report because like I said I'm having the same problem. The best thing you can do until you get it fixed is leave the fan on high(when the AC is on) and have all your vents open for max airflow. Right now is the season for both residential and mobile air conditioners to fail due to low psi/leaks, they pop up more than ever when the ambient temp is low and the units have not been run much due to season changes.

Hounddog

Mine does the same thing about every 40/50 miles on interstate.

CRXsi

Good point also TCR about the low pressure switches operation during normal AC operation. Hadn't thought about the dirty evaporator as yeah that could be possible also.

Hounddog

Evaporator should NOT be dirty in so short a period.My truck has only 17k on it.Had same problem at end of last summer and my neighbors also.I told service manager that BOTH would be back as soon as winter was over.I was right.I need to take it in.Last year they CALLED STAR on it and was told all was well with pressures etc.but it was start of fall and never used A.C.again on long trips.mine takes a good 50/60 miles to freeze up.As it thaws out it then dumps a LOT of water.This ttime I'll haunt them until its corrected.

CRXsi

Hounddog, based on what you say about driving 50-60 miles I believe this to be evaporator freeze up because of the large amount of water you are describing from the drain tube. In theory this would eliminate the drain tube being plugged as the water is indeed driping outside and not in the cab. I would say have your pressures checked and maybe even have the system evacuated and recharged to ensure 100% for sure that the system has the correct amount of refrigerant. If for sure there is not a refrigerant issue(either over or undercharged) then I would say it is safe to say the orifice tube or evaporator fin sensor is faulty or not functioning properly and causing too much refrigerant to go into your evaporator causing it to pull out so much heat from the cabin that it causes the moisture/condensation on the evaporator to turn to ice, once there is no more air flow over the evaporator it can no longer absorb heat from the cabin causing no more AC until the mass of ice melts and allows air flow again. I am not 100% familiar with Dodges AC system however the only way the orifice tube could be faulty to cause freeze up is if the internal orings have started leaking and refrigerant is bypassing the orifice. On the other hand I am not 100% sure what the evaporator fin sensors function is but I would assume that it tells the compressor when temps at the evaporator are too cold and shuts the compressor off. If this sensor were to fail the compressor may not shut off when it needs to and cause freeze up. I agree about the issue of the evaporator shouldn't be dirty (and this is not relevant to your situation) however dirty can mean several things...it could be a mouse has inhabited the space of the evaporator and built a nest plugging everything up or justa fluke of lots of debris, dirt or what not...strange things do sometimes happen.

CRXsi

Ok now that I have read the section in the manual fully it makes more sense. It appears there is no low pressure switch on our rams but instead uses what is called an "AC fin probe". Quote out of the manual is, " To maintain minimum evaporator temperature and prevent evaporator freezing, the AC fin probe, which is located in the evaporator, cycles the ac compressor by sendind an AC request to the JTEC which in turn processes this piece of information and if all conditions are met cycles the compressor clutch." So having said that I believe your AC fin probe/sensor is faulty causing the compressor to run until the evaporator freezes up.