ac comp on 300cd

[loneranger]

the ac comp on my 85 300cd is on all the time (clutch engaged), where do I look first? anybody got a wiring diagram for the acc on a 300CD? thanks

[rrgrassi]

Check the pressure switch on the dryer. The pressure switch is what completes the electrical curcuit for the clutch operation. It could be stuck closed, or some one could have made a jumper for it and left it plugged in. Check the switch for continuity.

There is also a test for the CCU, but I cannot remember what it is.

Also with the engine not running, but the key in position 2 (the one just before the starter engages and the glow cycle begins, IIRC), see if you can here the clutch engage and disengage with the key movement. If there is not audible clicking check the clutch clearance gap, and also check for 12 volts at the compressor clutch connector. Check it with the key removed, and in position 2.