1994 GMC Yukon Question: My 1994 yokun makes a hissing noise for about 10-15 seconds when a/c is shutting

I have owned this vehicle since 1994. The compressor/condensor was replaced as they said I had a leak. The noise only appeared after they replaced the condensor/compressor and the a/c filter. It has NEVER made a hissing "shut down' noise when I turned the engine off after running the A/C. And I don't hear that "shut down noise" in other cars either. The loud hissing noise just became after the repair shop replaced the A/C condensor and the "A/C/ filter assembly". The A/C works, just that there is a loud release of pressure that I have never ever heard before.....in mine, or any other car. Any suggestions.........do you think a hose or relief valve or something was broke when the re-einstalling the new parts?

Very difficult to say without having the vehicle in front of me. I personally have worked on and owned GM vehicles that did this noise and all was working perfectly. If it hasn't been done then have a shop replace the orifice, where the noise is happening, and see what happens. Typically though they are changed by the shop when any compressor is changed. You had not said whether it was replaced. It may be itemized on the compressor replacement bill.