I have repaired and troubleshoot this system so often I have come to the conclusion that it is too unreliable . A electrical bridge too far for the technology of that time period. The problem is in the controller, the downstream components are ok. Considering a series of switches directly to key solenoids to open van lines to enable functions. Up/down, heat, defrost. Anyone do this?
I havent done it , but agreed, the HVAC is too unreliable. The biggest factor in the holding the value down on e 23. the vacuum system plastic actuator pods are also unreliable. I once saw an e23 L7 with HVAC slide levers like on an e 30. would love to convert to that.