From dmasinick-at-mediaone.net Sun Feb  6 11:53:01 2000
From: David Masinick <dmasinick-at-mediaone.net>

Hi Mark,

There is a series of test that you need to perform on your system.  The
procedures are contained in the Heater/AC manual.  I will "email" you
through some of the tests.  You may ultimately find that the pushbutton
control unit is faulty, but it is a good idea to test out the system,
rather than throwing parts at it.  You can find rebuilt pushbutton units
for $150.

The first thing that you will need to do is to remove the glove box by
removing the 6-8 press-in fasteners.  This exposes you to the Climate
control amplifier and the interior temp sensor.

Although your symptoms don't seem to support this, you want to check the
foam tube that connects the interior temp sensor (the one in the center
of the dash)to the blower motor.  This tube provides the "draw" of
interior air through the sensor, so that it can sense.  If the tube has
disintegrated, you will need to replace it. You can test the air draw by
placing a piece of tissue near the little square opening on the dash
while the blower is operating.  You should find the tissue is drawn to
the sensor.

To test the control system, you will need to disconnect the battery, and
turn the ignition switch to the "on" position.  You will then remove the
12-pin connector (the pins are numbered)from the CC amp (it's the one on
the left, directly behind the glove box) so that you can perform some
resistance tests (you'll need an ohm-meter).

Try testing the following connections:

Test one: In-dash temp sensor and connection lines
Connect Ohm meter to sockets 1 and 6.
At 15 degrees C 	15.7 k-ohms +/- .5 k-ohms
at 20 degrees C 	10 k-ohms
at 35 degrees C 	6.5 k-ohms
at 80 degrees C 	(operating temp of coolant) 1.5 k-ohms
If out of range, replace sensor in dash

Test two: Temp sensor for heat exchanger
Connect ohm meter to sockets 6 and 9
Values the same as test one, but remember that this sensor is sensing
heater core temp, so if you the engine is at operating temp, you will
use the 80 degree spec.

Test three: Temp wheel test
Connect ohm meter to sockets 5 and 6, press center button (C) on
pushbutton control unit.
At 22 degrees C setting		3.15 k-ohms +/-.5 k-ohms
At Min and/or Max 		1.6 k-ohms
If values are not within spec, connect to sockets 5 and 7
At 22 degrees C setting 	3.5 k-ohms +/- 1.5 k-ohms
at Min and/or Max 		2 K-ohms
If both tests fail, try a new/used temp wheel
If temp wheel replacement fails, a new pushbutton unit is called for.

The next test (mono valve) is performed with the battery connected, and
the ignition switched on.
Connect to sockets 1 and 8
At temp wheel setting 22 degrees, 	15 ohms +/- 4 ohms
At Min or Max, 				infinity
Values outside range, replace monovalve.  If that doesn't cure it,
pushbutton control unit is in need of replacement.

Let us know what you find.

Dave Masinick  Hopkinton, NH
'82 300D  MBCA

> -----Original Message-----
> From: owner-diesel-benz-at-digest.net
> [mailto:owner-diesel-benz-at-digest.net]On Behalf Of Mark Fountain
> Sent: Sunday, February 06, 2000 3:11 AM
> To: diesel-benz list
> Subject: Climate Control Question
>
>
> I have an 82 300D with a climate control problem. The heater
> appears to
> be stuck on full no matter what the setting the temperature
> is. It's no
> big deal for me but it makes my wife really uncomfortable.
> I was told once that this might require a $500 part. Anyone
> have a clue
> on this?
>
> Thanks,
> Mark Fountain
> Vancouver, WA
>
>