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

oldsouth · #1 11-11-2004, 11:44 PM

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, 08:11 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, 11:56 AM

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, 12:53 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, 01:02 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, 09:48 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.

wir10 · #7 10-08-2006, 11:28 PM

1995 S420,

I have installed a 1.1k resistor (same part number from Radio Shack) across CTS, as per JimF instructions. Problem: Aux fans do not come on even at 100C.

I measured R15 and R15a resistors (at idle since I could not get the fans to come on) and read 0.9 ohm and 0.6 ohm respectively, which are the same as JimF measures.

I measured for voltage and current at R15 & R15a and got nothing. I assume the relay is open.

I also measured the CTS pins at 500 ohm at 90 degrees C, which indicates a good CTS (I also do not get a trouble code). I confirmed the cool harness 1.1k resistor also measures 1.1k ohm.

The funny part is that when I set my Actron Digital Reader dialer at 200 Ohm and measure across the 1.1k resistor attached to CTS, the fans come on. They do not come on however when I set my Reader at 2000 ohm.

Any ideas to what is happening?

p.s. I have not measured the relay, since I am nnot sure how to. The relay box seems like a box with a bunch of relays inside, hermetically sealed.

Robert W. Roe · #8 10-12-2006, 01:08 PM

When you say you are measureing ohms and the fans come on, it sounds like you are measuring resistance with the circuit energized; this is bad for the meter... pretty sure they use a voltage (the VOM's internal battery) to check resistance...