Audi 100/5k 1988 heater fan speed depends on cornering

Three possibilities: (1) a loose electrical connection that is being strained by centrifugal force while cornering. (2) debris close to the fan blades that starts to make contact during cornering, (3) a bad fan bearing.

Most likely the last of the three.

-- C.R. Krieger (Had a 2002 that did it. No; not a new Audi; an *old* BMW.)

Hi Jay and C.R.

Thanks for your replies.

What makes you think it's that?

It seemed to be more of a jump between high and low speeds, that's why I thought it would be a bad electrical contact and was mainly wondering where best to start to look for it.

I don't think it's (2), since I don't here any excessive noise when it goes slow. It makes more of a noise when it is blowing stronger, and that noise is the same it always made when it was running on full speed.

Thanks,

Christoph

Christoph. I had exactly the same symptoms, 1989 Audi 100 UK, removed the fan and discovered.........

Badly worn commutator & brushes to such an extent that there was a deep trapezoidal groove in the commutator. Remaining brush length was very short such that the brushes barely touched the commutator during straight line motoring. Hence slow speed running. However, on cornering, the end float in the motor allowed its armature to move axially. (The motor is mounted transversely in the engine compartment ) This in turn allowed the commutator & brushes to make better contact albeit on the sides of the worn groove in the commutator.

imagine a longitudinal cross section as below ...

brush ===)) comm. ((===brush

As the condition really deteriorates. No contact between commutator & brushes. No motor rotation Commutator moves vertically (in this pictorial representation ) during cornering allowing contact to be made. Motor runs.

I had to replace the motor as the commutator really was too worn to skim. Quite an awkward job to remove it. Motor cost about £60 GB from one of the European car part suppliers 2 or 3 years ago.

I have a vague recollection that there is some rubber pipework to either cool or extract dust from the commutator end of the motor, or grommets in that vicinity. Removal of this/these may allow visual inspection of the commutator. Alternatively you may find a way of applying an axial force to the motor to test the theory.

Good Luck ! Ian

Christoph, Yep, worn brushes and commutator on the fan motor. (BTW, excellent ASCII art Ian) The repair - although developed for 5k's in the US although it may be similar in RHD cars as well:

the author's revisions - you can find this and other postings on thesubject by searching Audifans archive for "steak knife"Cheers! Steve Sears

1987 Audi 5kTQ 1980 Audi 5k 1962 and '64 Auto Union DKW Junior deLuxes (SPAM Blocker NOTE: Remove SHOES to reply)

Hi Ian and Steve,

Thanks a lot for your help (and the artistic drawing). It sounds like a bit of a job, but I am quite sure that the diagnosis is right.

Just to make sure that the problem is in the blower motor and not anywhere in the electrical contacts, I would like to check the voltage into the motor. Is there any information available on the voltages the blower moter should get at the different speed settings?

Thanks again,

Christoph

Christoph, Maybe in the Bentley - Have you searched the Audifans site? (I did some free work for you if you didn't):

how about Scott Mockry's web site: ya go. Cheers! Steve Sears

1987 Audi 5kTQ 1980 Audi 5k 1962 and '64 Auto Union DKW Junior deLuxes (SPAM Blocker NOTE: Remove SHOES to reply)

The brushes are the problem - for sure.

If you want to do an easy test, remove plastic cover to gain access to blower housing. On the passenger side (of your car) of the blower housing there is a rubber elbow. Remove it and the brushes are directly visible. Use a wooden dowel or other non-conductor to lightly touch the brushes when they have power. This will alter the contact and make the motor run fast for a bit.

Your motor will quite completely within a month or so.

Tony

'91 100q 5spd fourth type 44 (have changed blower motors for this > >

Hi Tony, Steve and Ian,

It's blowing like never before ;-)

Thanks again for the advice. I opened it up, and didn't waste any time on electrical connections or anything else. You were right, the brushes are the problem.

That was the first surprise I came across: no rubber elbow despite the fact that everyone mentions it. And some yellow dots on the blower moter. I've only got the car since three years and someone must have replaced the motor before with one from the scrapyard (they tend to put yellow paint on to identify their items). The rubber elbow was missing completely, I don't know whether that's a problem.

Saw them and even tried to take some photos. If I ever get round, I might write a short text. Is anyone interested to put it on a web page?

Even a slight wobble on the cable made a difference. Then, I sprayed a bit of contact cleaner into it, and that made it run faster for a few seconds as well.

The commutator looked fine to me (no groove). It just seemed that the brushes were not touching any more. Their travel seems to be limited by the holder and the cable hitting the end of the holder. I unplugged the motor and used a small screwdriver to bend the holder down. A bit more contact spray and it now runs very smooth.

I hope I got a bit more time left (at least get me through our winter). I would like to find some replacement brushes. I didn't ring the dealer yet, but I am almost certain they don't sell them separately. Anyway, next time I go past, I will ask.

Thanks again for your help,

Christoph

Good to know you have the problem identified.

It shouldn't be a problem. The rubber elbow routes air from near the fan where the pressure is high through the elbow and directs it on the brushes. I would guess that it cools them and blows off dust and dirt.

I would like to find some replacement brushes. I didn't ring

Doubt that dealer will have brushes. Only sell the whole motor assembly. You could take the motor to an electric motor repair shop to get them replaced. I have heard of people finding generic brushes at local hardware stores and installing them. Still taking the fan assembly out will be a bit of a job so I would suggest letting a shop replace the brushes just to be sure.

Glad you found it.

Tony '91 100q 5spd