1981 Mercedes 240D Aux Fan - PeachParts Mercedes-Benz Forum

marco5 · #1 07-26-2013, 01:20 PM

Got my a/c system working. Yes, I know there are many threads on this (aux fan). I was able to find which relay which I tested to be good, where can I apply 12 volts to jump the fan?

Can I insert 12 volts directly into the relay ports? Please help

Mike D · #2 07-26-2013, 01:31 PM

The cooling fan relays on most Benz are activated by the completion of the ground/earth portion of the relay so adding an additional 12V power leg won't work.

To test the cooling fan relay you ground the 100C plug and the fan should engage.

For the A/C portion you jumper the pressure switch which will either be in-line or mounted on the receiver/dryer with the A/C engaged.

marco5 · #3 07-26-2013, 02:31 PM

A/C system works great, just the aux fan itself will not turn on. Okay I'll ground the 100C plug to see if the fan engages, is there anyway easy way of explaining which plug/hole this is?

Thanks for the reply

Phillytwotank · #4 07-26-2013, 02:55 PM

there is a "plug" for the fan on the driverside near the horn. you can unplug the wires and apply 12v there.

Phillytwotank · #5 07-26-2013, 03:22 PM

Also, you can "short" the wires plugged into the temp sensor on top of the drier. If the fan cones on with that test the relay is good and diner the fan is bad or the temp sensor is bad.

MBeige · #6 07-26-2013, 03:53 PM

Quote:

Originally Posted by Mike D

The cooling fan relays on most Benz are activated by the completion of the ground/earth portion of the relay so adding an additional 12V power leg won't work.

To test the cooling fan relay you ground the 100C plug and the fan should engage.

For the A/C portion you jumper the pressure switch which will either be in-line or mounted on the receiver/dryer with the A/C engaged.

Actually it's the temperature switch, and not the pressure switch, you need to ground to activate the fan. You can engage position 2 of the key (or have the car running). Disconnect the leads of the temperature switch (look for the pigtail harness on the receiver/drier) and bridge the two leads coming from the harness (not the pigtails). With the key in position 2 this should activate the auxiliary fan.

The fan should also have a plug located in front of the driver front wheel.