bgrabner

Mark,

Thank you for the FSM docs...I thought I PM'd you back but if I didn't, my sincere apologies. The font is light colored, but still readable - I have done a lot of the troubleshooting on it already, but I know I haven't checked the fan control unit specifically. You are very right, just because I have replaced it doesn't mean it or the connections are 100%. I guess I was thinking because the fuses have full power and the fan amplifier in the engine bay has full power, the control module should be in order. But, with the way this has been acting, there is obviously some connection somewhere that is not quite right...

Will keep you posted...

Bill

UKKid35

I just wanted to thank Dr Bob for his checklist. I followed the four page diagnostics in the WSM but this didn't uncover anything untoward (except the final aircon test which failed to give 7v).

However Dr Bob's list led me to the wiring of one of the two fans, as Pin 8 on the fan power amp cable gives infinte resistance to ground. I haven't yet fixed it, but I'm much more confident that I can than I was before I followed his advice.

The symptoms on my car are that both fans have failed, bridging the intake temp switch causes the flaps operate, but no fans.

Yesterday I found out the hard way that the latent pressure in an overheated 928 cooling system is not to be underestimated. Despite being cautious the pressure cap and a never ending fountain of coolant narrowly missed my face, and managed to remove most the the remaining hood insulating foam. Beware, the aluminium engine may not be the only thing you damage if you're not careful.

dr bob

Paul--

Check pins 5 and 8, the power feeds to the fan motors, for resistance to ground. If no continuity on pin 8, as you state, then unplug the fan connectors and verify that you have continuity between Pin 8 on the final stage connector to one of the conductors in one of the fan connectors. If no continuity, your break is in the wiring harness between the final stage connector and the fan motor. If you have continuity in that section, test the other pin in the fan connector for continuity to ground. No continuity means a bad connection to ground or a bad conductor in the harness. If you have continuity to ground in that fan connector, then check the internal resistance of the fan motor itself, pin to pin. That's the only piece remaining in the circuit, and open means the fan motor is bad. Just guessing from the fuse rating, internal resistance should be just a few ohms.

The wiring harnesses for the fans are clipped to the fan motor support frame with little metal friction clips. I added a bunch of plastic wire ties to make sure there is no flex in service, and minimal chance of the weight of the harness straining the fan motor connectors.

Ground point for the fans is MP-1 for your RHD car. This is the ground point that's on the front apron, on the left (pass side on RHD cars...) side of the car. This would be the right side, looking from the front of the car towards the rear. Per the WSM, there are separate ground wires for each of the fans to that point. Might be a worthwhile effort to pull those ground connections apart and clean them just to eliminate that possible failure point, as a first step. The wires and crimp-connectors on my car look like they need a little attention nowafter only about 20 years, and that's in a car that lives in a virtual desert, almost never sees rain and it never rains here anyway, etc.


HTH!

UKKid35

Thanks again to Dr Bob for his clear and precise advice.

The problem was the PO's repair, the fan leads which had been damaged at some stage had been wrapped in insulating tape which had melted causing the wires to short and fuse together.

The thing that confused me was that neither 30A fuse had blown when the fans originally stopped working, so I had assumed it was the control stage that was faulty rather than the output or power supply.

So pleased am I that the car is working again in time for our weekend away in France that I'm posting a couple of pics.

dr bob

Paul--

Glad you are on the way!

Oh-- Don't close the hood with the fan console stting out like that....

T_MaX

Years ago when I bought my 89 S4 I inherited almost this same problem! The only difference was mine was intermittent.

I went step by step checking everything that was mentioned above without much luck. One day I decided to pop the Central Control Unit (Fuse Box) out and manually jumper the fans leads from the back side of the fuse box (Home made jumpers with fuses).

As to date, I have never had any more fan problems!

dr bob

You can buy replacement "inserts" for the terminals in the main fuse panel from VW dealers.

T_MaX

Thanks Bob, do you have a part number by chance?

I would love to have it back to stock.

bgrabner

For what its worth - I started this thread, and I still have this issue I am pretty sure it is the fan assembly itself - this 928 has been pretty much stuck in the garage for the past 8 months though, so I haven't hastened to fix it

dr bob

I just take the old part with me to the counter. They have a box of assorted terminals and I grab the ones I need.

The PET manual shows them all, if you search under the 944 section. Look for single-pin terminals and there they are.


Most problems with fuse-panel terminals turn out to be melted fuse-panel plastic before the wires give out. You can extract the old beryllium-copper terminals using a dentist' pick to depress that little tab. Once out, you can squeeze them closed a bit to improve the connection. A squirt of De-Ox contact cleaner and the old one's are usually good to go. By the time the terminals get hot enough to anneal the metal. they've melted through the plastic fuse panel just a bit.

dr bob

Follow the diagnostic I shared for Paul's car. Same applies to yours.

I don't have any immediate east coast travel plans, but will be out there in Raleigh NC, probably sometime in mid November. Of course, by then you don't need the second fan...

In the meanwhile, give that wiring test a whirl! In another thread, somebody mentioned that the fan motor is common to more than a few cars like Saab and Volvo.

T_MaX

No worries mate! No one is trying to hi-jack your thread, simply passing on personal experience!


Disengage the fuse panel, than pull both of the fan leads (four) from the fuse panel, than install a temporary jumper on both. Start engine with A/C compressor switch in the on position.

_____________________________________________________________

Thanks Bob, I'll pop over to the VW dealership when I get a chance!

wds928

Bill:

We can tackle this at the TB/WP/Beer fest on Aug 5th at Chris'. I'll bring my multi-meter and the WSM pages. I had a similar problem and was able to fix it. Turned out it was my fan relay.