I will add some to Jims post...

There is a mid-production change on the E320, 124.032 chassis fan circuit.
First, there are now 3 fuses to be concerned with.
1- Fuse #7 in the fuse box. -- relay feed.
2- Both fan speed relays are now fused, [ on top of each relay].
These fuses are fan feed [load].
These are located behind fuse box, under panel. [Remove 6 screws]
The one in slot "C" is high speed fan [K9, blue one]. This originally called for 15A., but has been increased to 20.
Slot "B" is low fan resistor relay. This is 30A. [ K10,green relay]
This is resistor series feed for low speed. [ thus the higher Amps for lower speed].
PS - the fan load is always both fans, They are wired parallel.
So, first check is Fuses. The trick of jumpering the a/c high pressure sw. is that if that brings on low fan, you know you have good fuses #7 and relay fuse. Plus you now know your fans themselves are good.
Now we get to the high speed. [ which has nothing to do with low].
This is triggered by the temp thermistor sensor at the thermostat housing when the coolant temp causes the resistance in the sensor to DROP to around 275-300 ohms. This is a negatve temp/resistance type sensor. [ a good test is ohm meter ---- I have a temp/ohm chart , if need be]
This is the blue , 2 wire sensor everyone talks about, BUT, there is a late change-over to a 4 wire/prong sensor in 95.
The early ones had 3 sensors
1- single wire on top of housing- This is gauge sens .
2- 2 wire, blue on top of housing - this is aux. fan sens.
3- 2 wire, 3 prong on side of housing- this is Engine Management control sens.
The late ones have changed over to a 4 wire/prong sensor that now combines both the ECU and Aux fan sensors. The operation is the same, but one needs to know that the pins on the new one for the fan circuit will be pins 2 & 3.
This may add to/ or help clear up some of the confusion.
The main thing to do after checking to see which sensor your E320 uses is to check all fuses and then jumper the a/c sw to see where you stand and go from there with the sensor test.....