You need to diagnose the system following the factory service manual, which has about 21 steps to test all the sensors and controls, in order to really fix it right. Note that the FSM calls for a special adapter / tester unit that plugs into the two harness connectors for the PBU; you can figure out all of the component connections by studying the wiring diagram.

Guessing and shot-gunning parts gets expensive and frustrating fast.

My guess is that either your KLIMA is bad, or one or more of the inputs to the KLIMA are bad, so it cuts out the power to the compressor clutch. However, the PBU may be shutting down due to a bad component somewhere drawing too much power through the PBU. When the AC stops working, can you push the defrost button and get full heat on full fan through the windshield vents? If yes, than the PBU is probably not killing the signal, the KLIMA is.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC