[Vwdiesel] 2000 TDI a/c question - and a brief description of the A/C system

Tony and Lillie tonyandlillie1 at earthlink.net
Mon Jun 7 16:49:31 PDT 2010

Most of the questions have been pretty well covered. I've done some systems with professional equipment (working at a shop) and some without. I prefer the pro stuff, but wopn't spend the $$. As Loren mentioned, you only need a High side guage when troubleshooting. That's all I've ever used that reading for. I've filled quite a few systems with the simple blue hose with guage for low side filling. I go by the recommendations that come with it, and usually that amounts to about 40-45psi on the low side when I do them (that's in TX, BTW) How did you add some 134, with a simple hose, or with a gauge?

When you mention that the airflow is reduced, is that after driving for a while? If so, it sounds like you are icing up. Easy way to check, switch the AC off for a bit, but keep the fan on. See if the airflow comes back after a bit. You can switch off the recirculate to speed up the process. If it does, you are definately freezing the evaporator into a block of ice. Your thermocouple is bad, or something related to it. It sticks into the evaproator, and regulates it around 40 degrees F. 

I've personally never seen vent temps below 40 degrees, generally anything below 50F is sufficient. However, as close to 40 as you can get. On some of the older cars (like my 4000Q) the thermocouple relationship is adjustable, and I've got mine turned down to keep the evaproator at 34 degrees. However, I don't believe that's an option on the newer ones. I guess I've never checked that close, since I've never owned one ;-)


>I appreciate the explanations from all.  Combined with my rough 
>knowledge of the system and some half-remembered chemistry class 
>knowledge (I ran a supercritical fluid extractor in grad. school--forgot 
>about that), I think I have it.  Took me a few days to assimilate it 
>all, though.
>I always do worry about the big, catastrophically expensive parts like 
>compressors in a car with 267,000 miles, but I'll hope for the best.  
>Hope is cheaper.
>What seems to happen is that the airflow through the vents is reduced.  
>I normally run the system on fan speeds 1-2.  When the problem really 
>hit, I'd been driving almost an hour on recirculate and when I cranked 
>the fan to speed 4, all I got was a lot of noise and very little (but 
>cold) airflow.  Turning off the recirculate helped.  That was before the 
>added can of 134a, and I've not had to drive a lot since.  Tomorrow, 
>however, I'll have to make the same trip in even hotter weather.  I'll 
>let y'all know.  I'll also put on an extra layer of anti-perspirant, 
>just in case.

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