A/C problems in a 300TD

[bigrichard]

Symptoms:
Condenser fan does not come on. I tested fan with 12 volts and it works fine.
12v at one of the plugs on the drier (the one with 2 wires on the connector) when system switched on (and motor running)
Jumped plugs on drier and still no fan workie
Compressor comes on when it wants to. Can rev the engine and often hear the clutch click but not engage. Clutch does engages occassionally.
There is charge in the system (and oil)
Fuses are good.
I swapped ACCs with a good used one and still get same symptoms.
When the compressor runs while driving, the system does produce cold air. I don't operate it in traffic since the condenser fan is not working.
Ideas?