Seized fittings can cause great problems and leave you needing to replace more parts. So when installing a new a/c compressor, I have found it to be good idea to apply a conservative amount of anti-seize to the suction side fitting. Most fittings are metal and most compressors are aluminum. Since the suction side of the a/c system will sweat, this will cause the metal fitting to seize to the aluminum compressor back head. This normally results in the breaking, cracking, or stripping of the compressor back head when trying to remove the fitting in future repairs.
Fitting Seized to Compressor Rear Manifold
Broken Rear Manifold Due to Seized Fitting
Fitting Seized to Shaft