This is guesswork but, I'd look hard at activation and control circuits for the clutch. The posible players are relays, high/low pressure switches and temp switches for coolant temp. I know the 103 US/federal version has a 2 pole switch in the head for high speed aux. fan and clutch cutout.
I'd also look to see if the "thermistor" in the evap has electrical control. Some generic systems have one that is adjustable for clutch shutoff at certian temps.
There are also some compressors that have rpm sensors in them that if bad will cut the clutch and they are intermitent.
Hope this helps,
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.