Air Conditioning

1994, GMC Safari, 182553 miles, 4.3L V6 EFI, TBI, Front A/C only

I think it may be a VORTEC as the word is stamped on the intake, but I cannot find any documentation that indicates weather it is or is not.

Problem: The compressor is not engaging. Since my wife is the primary driver, she thinks that it stopped blowing cold air 'all of a sudden', within the past month. I think that there may be a blockage somewhere, but not sure.

Recent repairs: In July 2005 the following was replaced commercially; Compressor, Orifice Tube and Receiver dryer. System recharged and working fine.

Trouble shooting done since problem started:
1. All fuses that I could find are good.
2. Removed the Expansion valve in the orifice tube and cleaned it. There was lots of debri. Reinstalled and ran, nothing.
3. Installed a standard aftermarket R-134a recharge kit. When I hooked it up, the pressure guage didn't move. When I opened the valve to allow refrigerant flow, the pressure went straight up to 70 PSI. According to the guage, this indicates a mechanical problem.
4. I've checked all the vacuum tubes connected to the function lever and all appear to be connected and in good condition. Air blows to the different areas as the lever is moved. Just not cold air.

There is a sensor at the top of the accumulator, but I don't know how to check for validity or if it can be checked.