Radiator Fans - again

[insite]

I think it actually measures the surface temp of the the radiator itself. The part number is 996.616.101.00. I actually have my radiators out right now; I'll take a pic tomorrow.

[Dale_K]

The fans in my 2000 S seem to work together. I've never noticed only one fan operating. The Durametric can bring them on in high or low but not independently. I could see if the big resistor failed on one fan you'd get a situation where both fans would run in high, when the resistor isn't used, and only one fan would run in low.

I'm not saying you're wrong, only giving my experience.

[shlim8]

Originally Posted by insite

I think it actually measures the surface temp of the the radiator itself. The part number is 996.616.101.00. I actually have my radiators out right now; I'll take a pic tomorrow.

That's actually the series resistor... I'm going to order those online and replace it just to be sure...

[insite]

They do call it a resistor, but it looks like a thermistor to me. I bet yours has failed.

[shlim8]

My fans have finally gone crazy....

Yesterday when I started the car from cold, the fan comes on - as the a/c was on, I thought it was normal... checked the front and only 1 fan (right side) was running at low. I turned off the a/c and the fan now goes in to high speed AND again it was only on the right side...

Drive for the next hour or so, stopping where ever possible to check the front fans - still only 1 fan running at either low or high... (so at this point in time I'm thinking great, it's much easier to fix a permanent problem that an intermittent one)

When I got home, both fans are on at high speed... I let it run till it cuts out. Then I turned the aircon on, both came on at low speed.... $#@!!

Summary:
Engine cold - a/c on = one fan on low, sometimes 2, a/c off = one fan on high, sometimes none
Engine hot - a/c on = sometimes one fan, sometimes two fan
Engine very hot - sometimes one fan on high, sometimes two fans on high...

Any ideas ? I'm still thinking that something must trigger the fans, the dme ? But the dme must get it's temp input from somewhere. Or could the relays cause this ?

The series resistor might explain one of the fans not coming on at low speed, but now the other fan is intermittently coming on even on cold starts ?? (at least fans coming on excessively is better than not coming on at all !!!)

[shlim8]

Where are the relays for the aux fans ? Are they in the back trunk ? And which one ?

[Dale_K]

I saw a bunch of relays in the left rear corner of the trunk when I had all the trim panels out the other day but I don't know which, if any, control the fans. There was a little diagram as I recall.

[madmods]

Looking at spec sheet 5 (circuit diagram) for you it looks as if you need to go to the dealer and get them to initiate a full Cooling & AC systems test on yur Box. This is done from their PIWIS Tester II only.

There are relays for everything:

Cooling water Blower Motor 1 relay
- Relay Step 1
- Relay Step 2

Cooling water Blower Motor 2 relay
- Relay Step 1
- Relay Step 2

Ther is also a 3-lever cooling water switch which gauge low/high pressure and mean pressure. Those are linked to the relay circuitry.

Your problem could be anything in that range. To pin point it to the source, only the PIWIS tester II will be able to detect your fault.

Other than that, you have to rule out one-by-one and perhaps end up changing all the relays before getting to a point where it's not fun anymore to DIY. I've been there done that a few times :/