Testing the compressor first grab the center section of the clutch and see if you can turn it by hand. If not, the engine will need to be started and the clutch powered.
Jumping the pressure switch should power it, when the ac is requested.

It should engage, and pull a vacuum on gauges if no pressure is in the system. DO NOT RUN IT LONG WITHOUT FREON.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!