Either the engine speed sensor, the compressor speed sensor (if this car has one) is faulty or belt is loose/slipping on the compressor pulley. When the Klima relay detects a speed mismatch between engine and compressor rpm, it cuts off the compressor to protect the belt. The difference in speeds should be greater than about 30% to activate the cut-off. In the procedure I listed in this post, there are steps to check the voltage signals from these sensors.

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Saumil S. Patel