1999 Chevrolet Blazer

I have a 1999 blazer 4.3 liter engine 138,000 miles a/c
is not working. I checked all fusses, and have power going to the compressor. I have electronic climate control. I set it to recirculate the air, push a/c button on, set temp to 66 degrees, set to auto and yhe engine pulls down like the compressor kicked in and yet no called air. I checked the freon and added about 1/2 lb. Do the switches work off vaccum oe electric? : :
May 26, 2007.

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