1978 300D Electric Fan on Front Grill - PeachParts Mercedes-Benz Forum

supercub · #1 07-05-2011, 03:26 PM

Is the electric fan on the grill for AC, for the car's cooling system, or both? I have never heard it run. How can I test it? I have not had the car out in really hot weather, and my AC is removed.

Mike D · #2 07-05-2011, 07:29 PM

Ground the temperature sensor. There are two on your car. One works the gauge and the other is a "high temp" switch. The high temp completes the ground in the fan relay switching on the fan.

Yak · #3 07-05-2011, 10:06 PM

I'm pretty sure the electric fan on W123's is for the A/C only. No connection to the coolant temp.

Look for the thread on the The Don's new 240D in diesel discussion. He's got a good pic of a jumpered receiver/dryer temp sensor. If that's jumpered and the fuses and the aux fan relay are good, then the fan should come on with the ignition. The circuit works when the r/d temp goes above maybe 80 c (maybe wrong here, going off memory) as measured at the receiver dryer temp switch.

Without the compressor running and the refrigerant getting hot that switch would never close. Since your A/C is removed, no compressor and no refrigerant. Maybe even no r/d or temp sensor.

Benzcrusher · #4 07-06-2011, 09:21 AM

It's tied into the r/d temp sw and the temp sw on the thermostat housing. The relay for it is one of the ice cubes under the black cover just in front of the brake fluid res.

supercub · #5 07-06-2011, 03:56 PM

The only thing that was removed was the compressor.

Yak · #6 07-06-2011, 06:31 PM

Pic of a jumpered aux fan line in post 13 How to use Manual AC

Schematic of an aux fan in post 11 W123 aux fan not coming on

supercub · #7 07-07-2011, 11:17 AM

Would it be a good idea to wire the fan to teh compressor switch to use it in summer traffic jams? The temp does shoot up at times like those.

Yak · #8 07-07-2011, 08:47 PM

Quote:

Originally Posted by supercub

Would it be a good idea to wire the fan to teh compressor switch to use it in summer traffic jams? The temp does shoot up at times like those.

It depends. By "shoot up" do you mean approach overheating into the red? Or just go up to around 100 c? Are traffic jams frequent enough that this is common? Do you want it to be an auto-on above a certain temp, or manual "look the temp gauge is high let me turn it on..." Trying to connect it to the A/C compressor circuit would leave that decision to the vagaries of the CCU and your switch selection.

If it's hot all summer where you are (no location in profile) and there are no starting issues (e.g. a weak battery) you could just jumper the wires in the summer and let it run. Just remember to remove the jumper in the winter to help the motor warm up faster.

Since the A/C is removed you could do any number of things: a switch that senses ambient and shuts off at external temps below 50 f; a contact sensor on the radiator that turns it on above a certain temp.