Here is the situation.. I had about a 350 mile road trip today and it was around 95 degrees, had the A/C on the whole trip and about 300 miles into the trip I noticed that the air on all settings decreased in volume by atleast 50% if not more like 75% and the temperature of the air coming out was just slightly cool. When I finally got to the house I turned off the A/C, popped the hood, and grabbed a hose to spray out the condenser thinking that maybe that would help. After spraying out the condenser I got back in the truck and turned the A/C back on, immediately I noticed that the volume of the air came back to where it should be then a couple pieces of ice blew out the vent. After that the A/C appeared to be working properly. Anyone have any ideas as to what caused this? Something with the expansion valve possibly? This is the first time I have had this issue but I did buy the truck about 4 months ago w/ 35K miles on the clock.

 

what was the humidity
Clark

 

I wouldn't say it was overly high for Texas. I would put it probably around the 60-70% mark. When I popped the hood I noticed that there was quite a bit of water dripping off the accumulator.

 

Sounds like your evaporator was frozen. Could be low on 134A. You should have it checked.

 

Low charge will do this and there is a MEMO for a RELOCATION of the FIN TEMP SENSOR(thermostat) on the evaporator to stop freeze over.This has been a MUCH discussed topic since 03.Do a search.Lots of reading.If when the volumn decreases and you had turned the SNOWFLAKE(ac) off for a few minutes it would have thawed and blown cold again until freeze over etc.

 

I had to move my fin temp sensor as mine was doing the same thing but it does require removing the evap housing

 

Sounds like the evap was freezing over. Certainly could be caused by an improper sensor location on the evap. that cycles the a/c compressor on/off.

As to it being caused by a low refrigerant charge......that would be a new one on me. Someone would have to give me the long version of a/c theory behind this condition. Not that I don't learn something new everyday, but I have worked in and around auto a/c systems for 30 years and I have never heard of an a/c evap freezing up from a low refrigerant charge alone.

 

I'm not a ac expert but the LOW charge DOES cause freeze up.That same question has been asked and answered several times.Will some one else CHIME in on the reason of freeze over and uneven cooling because of a low charge condition.

 

When the unit is low on charge it is operating at a lower pressure, when the pressure is lower it is boiling at a lower temp. if it is boiling below 32 the moisture in the air freezes as it passes over the evap. ok now you ask how can boiling be freezing,the refrigerant in the evap is a gas and it changes to a gas by boiling,the compressor raises the pressure of the gas and it is condensed by the condensorback to a liquid.The metering valve or orfice then allows it to enter the evaporator at a controlled flow , the prssure in the evaporator is lower as and the liquid boils.if the fin temp sensor is incorrectly placed the compressor will run longer then needed and lower the evap pressure creating a lower boiling point thus freeze over . At 27.8 psi R134a is 32 degrees havent done ac in a long time but by temp pressure chart low side pressure around 55 should give an evap temp of 58 maybe a couple pounds less and ac should be cold and not freeze. of course how did it get low, LOTS of epa regs must be certified and use
containment recycling procedures.We all love to do it our selfs but no venting refrigerants to the atmosphere.

 

Thanks for all the replies guys... I will drop by a local AC shop and get them to check the charge on the system. Is this sensor that everyone speaks of located directly on the evaporator core? Where should it be moved to?

 

Star(D.C. tech assist)sent a memo out on where to relocate the fin temp on the evaporator.So many fins over/under previous location. The NEW evaporators have it in the NEW location.

 

I'm now into my third summer with A/C problems on my '03. Currently, my A/C compressor clutch does not automatically cycle on and off. I am consistently low on R134a charge about every 14 months, so I know that I must have a leak somewhere and a 30 minute vacuum test is now in order. The last two times I have had the system recharged, the evaporator will freeze over after an hour or so of driving. I have not had the fin temp sensor relocation done, so that will be next on the list after the system leak test.

Right now, after running the A/C for about 20 minutes, I get quite a bit of water condensing on the outside of the accumulator (#6 on the diagram). There is also condensation developing on the line (#2 on the diagram) coming out to the accumulator from the evaporator. The condensation from this line gathers on the retention clip (#3 on the diagram). The water from these two locations then drips off and flows down the inside of the right front wheel well liner.

Does anyone else who has a normally operating A/C system notice this amount of condensation on the accumulator? I would think this condensation is not normal for two reasons: 1) If the accumulator and lines have exterior condensation, then they must be at a surface temperature which allows the ambient air in the engine compartment to cool to 100% humidity and allow the condensation of the water vapor. 2) If the accumulator and lines are indeed cooler then the ambient air temperature, then the evaporator has done a poor job of heat transfer, as the R134a refrigerant is still cool when it leaves the evaporator in the line going to the accumulator.

My only other explanation is that the R134a leak is actually occuring at the line from the evaporator to the accumulator, or at the accumulator itself. The small R134a leak is then cooling the exterior of these parts to cause the significant condensation that is occuring. Any other thoughts?