Tha A/c panel must send a GROUND signal to the Klima relay for the compressor to engage. That signal comes in at pin 10 of the klima relay.

Also the tachometer must work & the RPM signal must come to the klima relay as well.

There is also an overheating switch on the engine that can stop the compressor from comming on. TRY disconnecting that switch to see if the switch is shorted.

Also on the accelerator linkage there is a limit switch that cuts off the compressor durning acceleration, try disconnecting that switch as well.

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