'96 Blazer a/c issue
 

Had a new a/c system installed except for electrical components. When it works it's fine. Sometimes when a/c switch is turned on I'll here a chirp. Sometimes I'll hear a constant squeal. 3rd new compressor. 2 different brands. It's definitely not the belt,it's tension,or other pulleys. It's as if the a/c clutch doesn't want to fully engage at times when a/c is first turned on. Any ideas?