Auxillary fan resistor 1995 S350 Diesel - PeachParts Mercedes-Benz Forum

oldsouth · #1 11-12-2004, 12:44 AM

My resistor for the auxillary fans in front of the condensor is bad and Mercedes parts said you have to buy a kit with 2 resistors instead of the pencil type that was originally on the car. Supposed to have 3 speed instead of 2. Does anyone know if this is correct and how will the climate control unit know there are 2 resistors there?

1995 S350 Diesel

mbdoc · #2 11-12-2004, 09:11 AM

The A/C/C system doesn't know a thing about the aux fans on a 1995 car!
Relays control the 2 aux fan speeds!
YES you need to convert back to the 2 "ballast" resistor system. I do have instructions if needed!

oldsouth · #3 11-12-2004, 12:56 PM

Thanks Doc. Yes I would like the instructions. Email - oldsouth@direcpc.com
Let me give you a little history about the resistor on my car. Originally it had the pencil type and it never worked from day one. The fans always came on high. No low speed. At the time I did not know it had a low speed. One time my car was in for something else, the mechanic said it seemed to be running slightly hot and needed a new auxillary fan resistor. I agreed and he installed part # 000 158 32 45. After this the car actually ran a little hotter than before but the fans did come on low instead of high. After a while, I just tied the two wires going to the resistor together and the fans went back to running on high and ran a little cooler due to being able to run on high when the a/c pressure got over 14 bar. I just recently pruchased a cool harness and the fans are coming on quicker now. I wanted to hook back up to the resistor to have low and high speed. I ran the resistor number by the parts guy at the dealership and he said it does not even come up as right for my car. So I ordered the following parts to convert it to the two resistor design.
000-158-37-45 Resistor
000-158-39-45 Resistor
002-546-30-40 Cable Shoe
140-620-71-14 Bracket
914126-006001 Screw (2)

Waiting on them to come in.

JimF · #4 11-13-2004, 01:53 PM

that control which resistor (resistors are R15 and R15/1) is in 'series' with the fan(s). The "logic" for this is deteremined by N22 as I told you when I answered your PM. This is the pushbutton unit located above the radio on the dash. The unit receives signals from the B12 (a/c pressure switch) and B10/8 (CTS sensor) and controls the starting point of the aux fans based on EITHER pressure with a/c or temperature (w/o a/c) in the engine coolant.

I think reference designators for the two relays are K9 and K9/1. If one is bad, that would explain why you had no low speed but had high. The table in my MENU #18 shows the switching points for either TEMP or PRESSURE.

oldsouth · #5 11-13-2004, 02:02 PM

Where are the relays and how would I test them? My car originally came with only a single resistor in front (slim pencil type). Would it be setup for the two resistor design? As far as I know it only had a high and low and no medium speed from the factory. How would only two wires going to the resistor work with two resistors? I have not received the parts from Mercedes yet so I am kinda in the dark about hooking it all up.

myarmar · #6 11-13-2004, 10:48 PM

According to ETM three stage setup with low, medium, and high speeds was used only on 92 models. It had 2 relays K9 and K9/1 (K9 is actually a module with two relays inside), and two resistore R15 and R15/1. As of 1993 and up to mid 1995 MB used only two speeds. Only one double relay K9 was used, no K9/1. From mid 95 electronic module with infinite speed control was installed, no relays and resistors.
You can connect two new resistors in series configuration and use it as with you original setup with two speeds - equivalent to low and high in 92 setup. It is also posible to wire for medium and high if you put wire from the relay to the middle point of two resistors.

JimF · #7 11-14-2004, 01:09 AM

because my '94 has three speeds and so do the '95s (I think).

OS, you need to get a CD-ROM and they usually contain schematics that would allow you to re-wire the system if you so choose.

But as I've said in PM, 'low' and 'high' with my Cool Harness would suffice since the car will not need the 'medium' speed since the CH cuts the fans in early to avoid the higher engine that's generated without one.

oldsouth · #8 11-14-2004, 04:18 PM

I checked voltage output at the resistor that is currently in the car and it read almost 9 volts. According to your chart Jim, that is medium speed. The resistor is what determines the output voltage, right?

JimF · #9 11-14-2004, 05:05 PM

determine voltage, the battery/altenator does! A resistor drops voltage due to power loss.

It's difficult to know what you measured; across a reistor or to ground and where the reference points are. Also we (and YOU) don't know how your car's fans are wired. A schematic for your car and then verification will allow us to proceed.

Then knowing how it's SUPPPOSED to be wired we could assist to in re-wiring it. We will have a common base from which to proceed.

oldsouth · #10 11-14-2004, 05:22 PM

Clarification - Grounded one end of voltmeter and the other end I attached to one wire then the other that attaches to the resistor. With the fans on low, one wire read over 12 volts (system voltage) the other read a little less than 9 volts (output voltage after going through the resistor I guess). What I was wondering if different resistors had different output voltages going to the fans on any certain speed. It is apparent the resistor on the car now is not what the book calls for. I think the parts man said it was for a 123 series car. I am looking now at the service DVD but am sure the wiring has never been altered from factory specs. I have had the car since new.

myarmar · #11 11-14-2004, 07:31 PM

9 Volt is equivalent of medium speed in 3 stage setup. Why do you want to replace resistor? Looks like it is OK. But you need to verify high speed.
Here is a page from ETM as of 1993.

myarmar · #12 11-14-2004, 07:35 PM

And this is for 1992 - 3 stage setup. But was used on later cars also per JimF?

JimF · #13 11-15-2004, 01:16 PM

great schematics!

I've resized and cropped them abit so they fit in a smaller jpg format. Thought I'd attach your great work, so we all can talk to them. Tnx again.

Yes, my '94 is the tri-speed system.

JimF · #14 11-15-2004, 01:34 PM

are labeled 000 158 37 45, measuring about 0.03 and 000 158 39 45 about 0.04 ohms. A disclaimer: I didn't remove them from the ckt so I'm reading the parallel resistance value.

I believe I measured them out-of-ckt and the values were about 0.06 - 0.08 ohms.

The dual fans impedance is about 0.38 ohms so the values above seem a bit low. If I get some time I'll remove them to make an accurate measurement. But the point is you don't need a high value to slow the fans.

At 0.06 ohms those 'dropping' resistors are dissipating 55 watts or so. That's why they are mounted in the front.

myarmar · #15 11-15-2004, 07:47 PM

Found more info in WIS. The fact that you have two resistors in the car doesn't necessarily mean 3 stage setup. It all depends on the connections and jumper. This is up to 11/30/94