Auxilary cooling fan not working
 

Idling in (God-awful heavy) Atlanta rush hour traffic this week with A/C on full blast I notice motor temp inching past 100C. :eek:

Off goes the A/C and the temp comes right back down. :D (Relief) If the car is moving with the A/C on, it does not begin to run hot. On further thought, I realized that last week I could hear the auxilary fan coming on and I no longer hear it turning on.

Where to start to trouble-shoot? It is not the fuse, that is all that I know for sure - the fuses are all fine as I checked them last night. I believe there's a pressure switch on the A/C drier that is NOT to be messed with lest I discharge the A/C (I am a total novice when it comes to A/C) as well as another switch that might be my problem.

Vehicle (in signature) is '83 300CD (turbo.)

The pressure switch on the drier is for the a/c compressor, not the fan. The fan is actuated by a temp switch on the drier. The temp switch is usually above the pressure switch and has two wires (pigtails) that are permantly attached to the switch. (The pressure switch has two bayonet spades where wires attach.) If you jump the temp switch wires together with the ignition switch in the "Run" position, the fan should come on.

If your a/c refrigerant level is a bit low, the temp may never get high enough to trip the switch. The switch is operated by refrigerant temp, not coolant temp.