Well I held off as long as I could, but I need some clues, here's the basic story:

84 Euro 280CE with basic HVAC like a US 240D, not Climate Control.

Just had a hose replaced after it leaked last year, so the A/C been out for a few months. The problem now though is with the compressor clutch.

With the key on, but the engine not running, the clutch will click on and off when you turn the switch, however once you start the engine, the compresser will not engage until you turn off the A/C and then turn it on again. After this initial start the A/C will cycle all day long untill you shut off the engine, then you have to go through the same proceedure after you restart the engine.

My guess is to do with the draw of the starter while cranking, but where should I go from there?.

PS maybe it's time for a dedicated A/C forum, next to spark plugs and synthetic oils LOL