1988 Audi 90 Quattro

[Huw Powell]

> > > >>Heating unit for the car seats clicks when it has been on for a while.
> >
> > > Mine too, the clicking sound is from under the dash and I make it go
> away by
> >
> > This is "normal" - it is a thermostatic system and once the seat is up
> > to the preset temp, the relays will turn the heater on and off
> > perdiodically.  Although sometimes it seems like they do clatter rather.
> 
> That's a good point.  The original post doesn't mention rapid clicking with
> a frequency faster than the turn signal click.  That's the problem with my
> car and was not necessarily the question being asked.  (D'OH!!)  I'm pretty
> sure this rapid clicking my seat heater relays have isn't the normal
> thermostatic control of the heating element, though.

I think it is, but not working properly.

Any thermostatic system should have a window between open and close
settings (um, what's that called, I knew this once!).  If they are too
close (for some reason) the system will cycle too rapidly, either, say,
stopping and starting hot water pumps too often, or in the case of seat
heater controls, overworking those poor relay contacts and probably
hastening their final demise.

Maybe the problem is that they don't quite "make" properly, so they
"unmake" and then try again?

Mebbe someone with the problem could dissect one of their seat heater
control units and take a look.

Mine does it "sometimes," but too rarely to open one up and fiddle with
it.
It could also be due to a flaky seat thermostat, goofed transistor
thingies in the control unit, or a few other things I am sure others
will chime in with...

Swing!  that's what the difference between turn off and turn on is
called.  Typically about 2 degrees F for a home heating thermostat.

Now imagine what would happen if there was an intermittent, but usually
good, contact in the seat thermostat.  every time it "breaks", the relay
turns off.  then back on when it "makes" again.  or vice versa,
depending on whether the thermostat is NO or NC, I guess.

-- 
Huw Powell

http://www.humanspeakers.com/audi/

http://www.humanthoughts.org/