I am working on my fathers 1991 Dodge D250 AC. The truck has a 5.9L diesel and the AC runs constantly, there are no bubles in the site glass, the low side pressure is 90psi, and the highside is between 90 and 100psi.

I am trying to determine if I have a bad thermoststic clutch cycling switch, as stuck expansion block, or a bad compressor. The factory service manual says to check the clutch cycling switch for continuity and I can not find any description of which combination of the three pins on CCS should have continuity or if all should.

Can anyone explain what I the real test procedure is for check continuity of the CCS?