I see your post has been in a while and no responses, I just joined and might shed a little light on the subject.
My 97 Savana has just undergone about $1100 in A/C repairs, and after replacing compressor, fan switch, and misc other parts, still had a similar problem with yours. I took it back and had them check out the system once again, and found a cracked vacuum line hidden under the unbelievable amount of crap under the hood. They fixed that and bingo, full flow. Hope this helps.
Monday, September 3rd, 2007 AT 11:14 AM