AC compressor clutch not engaging

[Dead Parrot]

No or too low freon equals no or short clutch engagement.
Double check belt tension. Normally belt slippage is fairly noisy but possible a foreign tractor came with silent belts? Or you have a oil leak somewhere and the belt is too wet to make noise.

The old A-6 and A-4 GM compressors could have their clutches replaced while on the vehicle and without draining the freon. No clue on yours.

[RustyPile]

Originally Posted by Dead Parrot

No or too low freon equals no or short clutch engagement.
Double check belt tension. Normally belt slippage is fairly noisy but possible a foreign tractor came with silent belts? Or you have a oil leak somewhere and the belt is too wet to make noise.

The old A-6 and A-4 GM compressors could have their clutches replaced while on the vehicle and without draining the freon. No clue on yours.

We need to know how the freon system is designed on his tractor. Some systems have a suction throttling device that controls the amount of freon pumped by the compressor. On this design, the compressor doesn't cycle off and on, rather, it runs all the time. This is how the compressor operates from the factory on our 68 - 72 trucks. Cycling clutch designs cycle the compressor off and on to control the amount of freon flow and will "short cycle" in the event of low freon.

The OP stated he has checked for voltage at the compressor. I assumed (could be an error on my part) he meant the voltage was present when the clutch was not engaged. That information led me to my diagnosis of a clutch gap issue. The proper way to check voltage at the clutch is to leave the plug connected and probe the connector while the AC is operating.