W124 Auxiliary Fan - Page 2 - PeachParts Mercedes-Benz Forum

Bio300TDTdriver · #16 06-25-2011, 04:28 PM

Quote:

Originally Posted by Jeremy5848

Thanks, Sixto, I'll revise my list.

Comment: The OE switch in the 1987 300D/TD does not turn off the a/c compressor until the coolant gets to 128°C. In my opinion and Sixto's, this is waiting much too long and may be one reason why this engine is known to crack its head. Replacement of this switch with one of the others, mechanically and electrically identical except for the temperature settings, is advised. About $30-40 new from your dealer or $5 from a wrecking yard.

Mercedes-Benz auxiliary fan (high speed) and compressor cut-out switch part numbers are:
• 006 545 64 24 (used in OM603 of '87 300D/TD only) 105ºC/128ºC with blue top
• 006 545 42 24 (used in M102 and OM601 engines plus OM603 of '86/'87 300SDL) 105ºC/120ºC with gray top
• 006 545 45 24 (used in some M103s) 105ºC/115ºC with green top
• 006 545 61 24 (used in M102-3-4 and OM602 engines) 100ºC/110ºC with red top

Don't forget to install a new crush washer if you change switches.

Jeremy

Jeremy, you have the red and grey numbers reversed.

Chris

the tenor man · #17 06-28-2011, 10:06 AM

When my auxiliary fan wouldn't operate, it was the step down resistor...it was cracked and broken from age.

As I have the #14 head, I was always afraid I would overheat the engine.

I removed the resistor from the circuit and used a small bolt and nut to connect the wires, then used shrink wrap tube to seal them.

Now when the pressure goes up on the AC, the fan runs at high speed...no low speed anymore, but who cares...I'm inside the car in the cool!

The Tenor Man

Jeremy5848 · #18 06-28-2011, 11:32 AM

Quote:

Originally Posted by Bio300TDTdriver

Jeremy, you have the red and grey numbers reversed.

Chris

The list in post #13 is now corrected and I made a couple of additional comments. Chris, thanks for catching the error.

Jeremy

jfikentscher · #19 06-28-2011, 12:20 PM

Where is the step down resistor???

Jeremy5848 · #20 06-28-2011, 01:04 PM

IIRC, it's screwed to the left inner fender, low down, just behind the left headlight. I have a picture somewhere, let me confirm & edit this post.

Edit: Yes, it's next to the ABS pump (between it and the fender). For pictures, see my post #18 in this thread.

Jeremy

Mainard · #21 01-26-2019, 09:44 PM

If anyone wants to check the relay, it is relay C.

Mainard · #22 01-26-2019, 09:45 PM

Relay C is the second relay back behind the read cover of the fuse box. In order to get to the rear fuse box, you need to take the six Phillips head screws out of the fuse box.

luism · #23 06-05-2020, 04:58 PM

Quote:

Originally Posted by sixto

The aux fan's low speed circuit doesn't respond to ambient or system temperature, it responds to refrigerant system pressure. The FSM suggests the high pressure switch triggers the aux fan at 20bar/290psi. Bridge the pigtails on the high pressure switch with the engine running and compressor engaged. If the aux fan doesn't come on, it could be a bad relay, bad step-down resistor, bad fan or bad wiring. If the aux fan comes on, the relay is fine but it tells you nothing about the switch. I suppose you could put a gauge on the high side but I don't know how you force 20bar at the receiver/drier without the risk of overheating the engine.

Sixto
87 300D

So unless, I refill more R12 into the system about 290psi on the high side, the auxiliary fan will turn on. Is this right?. Right now I have it about 190, the AC seems to work fine but no Aux. Thanks.
-Lui

240dddd · #24 08-20-2020, 03:52 PM

I'm resurrecting the AC in my 87 300TD. I have it to the point where it is charged and compressor is coming on, however the aux fan is not coming on when the compressor is engaged.

As a troubleshooting measure is temporarily bypassing the step down resistor as described by "the tenor man" a bad idea? Or are there potential electrical problems introduced by doing this?

Quote:

Originally Posted by the tenor man

When my auxiliary fan wouldn't operate, it was the step down resistor...it was cracked and broken from age.

As I have the #14 head, I was always afraid I would overheat the engine.

I removed the resistor from the circuit and used a small bolt and nut to connect the wires, then used shrink wrap tube to seal them.

Now when the pressure goes up on the AC, the fan runs at high speed...no low speed anymore, but who cares...I'm inside the car in the cool!

The Tenor Man