Heating control always on?

[Huw Powell]

> Daughter's '88 90 has a problem that just started today.  The heating
> element for the driver's seat stays on unless the car is shut down.  No
> modulation, and even though the setting is set to 0, it seems to be on
> full. 

There are basically three places the problem could occur - in the little 
controller wheel on the dash, at the thermistor thing in the seat, and 
at the control relay.

It's unlikely to be the dash thing, since it is just a variable 
resistor.  Though, it could have an internal short.

If the seat thermistor was bad, all it could do is "call" for more heat 
when the control is set for some, so it's also unlikely.

The control relays are not only most likely, they aren't terribly hard 
to diagnose.

Undo the cubby panel under the steering wheel (four screws with 8 mm 
heads, I think), and you find the auxiliary relay panel, which has about 
three rows of relays.

Look for two identical relays next to each other - they are tall ones, 
and probably have part number 443 919 533 on them.  Pull them out and 
swap them wiht each other.  If the problem goes to the passenger seat, 
one was bad.  Pull one out and see which seat it ran, discard whichever 
one wasn't working (or open it up and try to fix it... it may just have 
stuck contacts).  Replace with one from a junkyard.

If the problem stays where it is, the dash controls can be pulled out 
with a pick type tool, and likewise swapped to see if one of them was 
the culprit.

-- 
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/