I'd say the Klima relay is flaky. Maybe JamesDean can rebuild it. I don't think more commonly available gasser Klima relays work with Diesels. You can substitute a simple on/off relay for the Klima relay but you loose the features that cut power to the compressor clutch if there's an rpm disparity or engine temps run high. At least try the simple relay to confirm the problem is with the Klima relay.

Sixto
MB-less