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doug - 28 Jul 2006 01:02 GMT

I have a 1983 380SL at work and the HVAC blower won't come on. The
blower motor has been replaced and the blower speed control module
behind the glove box has been replaced. The ducts switch when I push
the buttons and if I take the cover off of the old module and close a
relay with my fingers the blower comes on. Four relays, four
speeds...so I guess the motor, resistor, and associated wiring is ok.
Any help, suggestions, or wiring diagrams would be wonderful. Any
part failures that are common? thanks in advance,

doug

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T.G. Lambach - 28 Jul 2006 02:13 GMT

Isn't the blower switched ON / OFF by a vacuum switch?

Older, "servo" cursed 116s and 123s switched it that way, your more
modern version may differ.

Since you asked - my 2 cents.

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pdrahn@coinet.com - 28 Jul 2006 19:39 GMT

> I have a 1983 380SL at work and the HVAC blower won't come on. The
> blower motor has been replaced and the blower speed control module
[quoted text clipped - 6 lines]
>
> doug

I wonder if you have the same problem my wife's 1983 300SD had. Two
different dealers worked on the problem over several years and all were
just expensive temporary fixes. The fan was replaced because the motor
was "bad". It fixed the problem for about a year. I kept the fan and
years later hooked to 12v and it ran just fine. Another dealer
replaced the resistor box because it was bad. I didn't keep it, but
this fix lasted only 3 weeks.

So, the only thing left was the push button control box. It was
replaced and it did cure the fan problem. Total cost for fan problem is
probably over $3,000. I have been afraid to add it up!

Being the curious type, I disassembled the old control box. We have all
heard and experienced German engineering, but down at the circuit board
level, there is engineering that should bring shame to all German
engineers. The main circuit board has two daughter boards attached to
edges of the mother board with only solder fillets. Over time and
vibration, some of the solder fillets developed cracks and eventually
opened up the circuit.

When the fan and resistor box were replaced, the connecting cables had
to be disconnected and reconnected to the controller. When this was
done, the flexing of the plastic housing and circuit boards forced the
solder breaks back into contact and the whole thing worked for awhile.

The control box was a real bugger to replace as all the "wood grained"
material on the center console had to be removed. So, naturally the
service manual says to replace all the other components first. Dumb!
The controller was designed to fail!!!!!

So, I don't know if this helps or not, but may give insite into the
potential source of the problem.

Good luck!

Paul

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Richard Sexton - 28 Jul 2006 22:57 GMT

It's nearly ALWAYS the pushbutton assembly that fails. The fan gets weak
long before it fails as the brushes wear out then the brish holders act
like lathe cutting tools on the shaft. The poor fangets slower and slower.

When the pushbutton unit fails it fails usually by having only one or
two button work then one day - nothing. The time between one button failing
and the whole thing failing was in my case about a week. I suspect, but do not now
for sure it was related to having a high power stereo installed below it and
running both on a hot sumemrs day.

As you say, onc eyou look inside those things you get a bit quesy. But, they are
state of the art 1970s technology because that's exactly what they are much in
the same way the shuttle still uses core memory and 35 year old computers.

The pushbutton assemblies can usually be found for about $50 used on ebay.

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Richard Sexton | Mercedes stuff: http://mbz.org
1970 280SE, 72 280SE | Home pages: http://rs79.vrx.net
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doug - 15 Aug 2006 02:08 GMT

for all those who offered help, it is appreciated. it turned out to
be the control head in the dash. I borrowed one from a friend with
the same car, 10 minutes out and in and it worked. Ordered up a reman
and all is well. thanks again,
doug

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