Ventilation Fan - Only Working on No. 4 ??

[alane]

Hi All,
The ventilation fan on my '87 944 has today decided to only work on 'No. 4 Setting'.
Has anyone any ideas what might cure this ?

No. 4 operation/speed seems to be the same as the 'Rapid Clear Screen' button.....so do I presume No.4 is not linked to the 'main fan' ( ie. No.1, 2 & 3 setting ? )

I've checked various fuses where the schedule mentions 'fan or cooling or ventilation' but all are fine.

This is the first electrical problem I've had since owning the car.........
Any help is appreciated as always.

 

[sawood12]

This is a well known issue with 944's. There is a set of resistors that are bolted into the fan unit behind the bulkhead where the wiper mechanism is. It is a small module with three coils/resistors, one for each fan speed setting. It just so happens that speed 4 is full 12v applied to the fan so is a fail-safe mechanism that allows the fan to always run at setting 4 if this module fails.

If you remove the module you can use a bit of Scotch Brite on the contacts which sometimes work, but sometimes it needs replacement. A 2nd hand replacement item is around a tenner but the OPC want about 125 quid for a new one!!!

 

[alane]

Cheers Scott
Much appreciated..........I'll have a look

 

[James_G]

Andy, did you get this one solved? Mine's just started doing this today too.

Cheers

James

 

[alane]

Hi James
I haven't had chance to look at it yet (work & family !) but I have found a website with photos of where the problem may be. This also is inline with Scotts advice above and other websites.
http://www.944time.com/porsche/944-fan-speed-resistor.php

It seems like the 'resistors' are on top of the fan housing. The fan housing is located under the 'very thin plastic' liner(full width of car virtually), under the bonnet. The one glued to the bottom edge of the windscreen.
I think the resistors are on the top of the fan, central ish about the car........
Let me know if you have any success.

Does anyone know how much the 'thin plastic liner is ? as I'm sure it will be kn*ckered once its taken off !
Cheers

Andy

 

[James_G]

Thanks Andy, a job for this week. I'll let you know how I get on.

Cheers

James

 

[James_G]

Managed to rescue the ballast resistor (or whatever it's called) from the car and the first point is that Andy, you were right, the plastic trim is easy to break. Luckily a previous owner had done this for me, so it came away easily. The leading edge is held under the rubber seal that runs along the bulkhead. The rear edge is glued, but also pinned in under the wiper arms.

Having got it out, here's what it looks like:

Firstly there's some horrible rubber gunk around it and I'm not sure if that's been added post factory. Also you can see what looks like a micro-switch in the shot, and I am not certain what it is for, although it could be some form of bi-metallic strip. I put a multimeter across the different coils and was expecting vastly different readings, but they were only varying by 1 ohm or so. Basically, it looks sound, and so I am going to clean up the pins and then re-install it to see if it makes a difference. For reference the fan works on speed 4 without it installed, although whether that's a good idea I'm not sure.

Anybody got any info on the different resistance readings to be expected?

 

[pauljmcnulty]

Can only add that mine doesn't have any gunk around it, and all the little brass bits fell out when I removed it.....[]

 

[James_G]

Thanks Paul, this does suggest that somebody has fiddled with it in the past, so that's one problem solved.

I'll post more when/if I get it sorted. Can't believe it's £125 from Porsche - there's really not much to it unless the coils are made from unobtanium[]

 

[sawood12]

Crikey , mine looks completely different to that one in the photo. I also bought a 2nd hand one which I never got round to fitting as my fan started miraculously working since I bought it so i'm saving it for when it starts to go again.

Seems like this should be a pretty simple project for someone who knows thier bottoms from their elbows when it comes to electrics and electronics and re-manufacture one or something that does the same job. After studying the module I struggle (with my rudimentary electronic knowledge) to understand how it works.

By the way the plastic rain tray is around £60 IIRC but the OPC to be ordered specially from Germany. When I bought mine I had to wait a few weeks for it as they had to have another batch manufactured.

 

[James_G]

Hi Scott,

Thanks for the detail on the plastic trim - something to consider. Meanwhile the part number for my resistor is:

944.616.105.00

Different to yours I am guessing?

 

[sawood12]

Haven't got a clue what the part number is i'm afraid. I've never seen the one that is actually in my car. I started having intermittent problems with mine last year, and after reading up on it and identified the problem I priced up a new one with the OPC. After picking my jaw up off the floor I went along to my local breakers who went into his aladins cave of bits and came out with one that looks completely different from the one in your photo. He didn't query me on model, year or part number so I assumed they are all the same.

Having said that when I removed my current rain guard I saw the back of the module installed in the fan unit and it looked the same. I'll take a look at it tomorrow and let you know. I didn't bother replacing it at that point as it is working fine at the moment so I didn't want to disturb it just in case the 2nd hand module I've bough is no good (always a risk with 2nd had gear). You know how temperamental electrical stuff can be.

 

[James_G]

Just resurrecting this thread in case there are any more of you having this trouble. I cleaned up the pins on the resistor pack and the connector block sockety bits with some emery paper and put it all back together and it all works again.[]

So that, along with the gearbox oil having been refreshed today means it has been a good day!

 

[NeilW]

This thread must be a candidate for the FAQ sub-forum.

 

[wibble]

Definite FAQ - mine needs doing as well, just never got around to doing it.

 

[sawood12]

Just got the multi-meter out on my spare and it seems a very simple device. There are 4 resistors which are simply connected in series so when you turn the switch the current is switched through 1 resistor, or 2, or 3 or 4. The problem seems to be that there are two break contacts - one positioned under resistors 1 & 2 and the other under 3 & 4. I assume these break contacts are bi-metal strips just in case the resistors overheat it will cut the current. These contacts seem to be prone to oxidising and therefore breaking the circuit. The reason position 4 always works is because even if both contacts are broken you always get a completed circuit through fan position 4's resistor.

So I guess the action of cleaning up these contacts seems to fix the problem more often than not.

 

[pauljmcnulty]

This thread must be a candidate for the FAQ sub-forum.

Definately - all it needs is me to have the time to get the damn thing written......[&o]

 

[wibble]

Thanks for the tips - got mine working with the help of the missus nail file

 

[Pastry]

wee bump for this topic (before it gets lost in the mists of time)
mines started doing the same thing. hopefully i'll sort it out on friday, take photos and write it up.


http://www.944time.com/porsche/944-fan-speed-resistor.php

 

[pauljmcnulty]

I'd be careful putting a blade in to clean the contacts as that article suggests, they are very delicate. A careful squirt of contact cleaner is a safer bet.