300D Aux. Fan doesn't work
 

I have a 1983 300D Turbo. Car has 177K miles. The car has never ran hot until recently. I have found that the aux fan is not cutting on. I have checked the fan by jumping it to 12 volts and the fan works. The day this problem occured a red fuse was blown in the fuse panel. I replaced the fuse, but did not fix problem. I have swapped the A/C relay with the fan relay and no fix.

What else do I need to check.

You need to check your a/c pressure switch located at the dryer. You should be able to "jump" it to make the switch come on. If, when you "jump" it the fan comes on either your switch is not working or your a/c pressure is not high enough to activate the switch.

The aux fan is not there to prevent the engine from overheating. it is there to bring down the high side pressure when it gets too high. Blowing air across the condensor brings down the pressure rapidly.

Good luck,

I have been having a similar problem with my 82 300SD, although it never overheats. I hit the aux fan with 12V and it came on, but jumping the pressure switch doesn't make it come on. I then replaced the aux fan relay, but jumping the pressure switch STILL doesn't make it come on. I've check and replaced the appropriate fuse, even though it wasn't burnt.

Aux Fan
 

1084 300d Turbo
The Pressure Switch Is For Low Gas Pressure That The Compressor
Is Off Some Have High-low Press In One Sw On Rec-drier Cuts Out
The A/c Compressor To Low Or To High
The Temp Sw Is For The Aux Fan Can Be Remove Any Time Only A Probe
In The Rec - Drier 5 Min Done. Short The Wires To On The Fan