A/C - Tempmatic Climate Control Diagnostic Tips
87mercedes03TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS
DATE: January 1987 (supersedes MBNA 83/11b, Dec. 1985) REF. NO. MBNA 83/11c
SUBJECT: TEMPMATIC CLIMATE CONTROL MODEL 201
This Service information updates previously published information to include
Model Year 1987 vehicles.
A. Pushbutton Control Unit Replacement
Complete pushbutton control units must not be replaced for either a defective fuse (part no. 001 545 04 34) at the rear of the unit or a defective lighting circuit board (part no. 201 820 07 77). Both of these components are available as separate replacement parts. Refer to the Introduction manual M.Y. 1984 for repair instructions.
Effective immediately, warranty will be rejected for complete pushbutton control units returned for either problem.
CAUTION! Interchanging the plugs on the pushbutton control unit will blow the fuse mounted at the rear. The left plug is marked with a red band (arrow) on the harness tubing and should be plugged in on the selector wheel side of the pushbutton control unit.
Note: As of MY 1987, the fuse has been deleted on the pushbutton control unit. It is protected internally. The MY 1987 version is not interchangeable with earlier versions (see Parts Information).
B. Feedback Potentiometer Adjustment/Replacement
Please be advised that adjustment/replacement of the blend-air feedback potentiometer (top of heater case) should only be attempted when it fails the tests described in the Introduction Manual M.Y. 1984 (Model 201, group 83, pgs. 134- 136).
The internal electronics of the pushbutton control unit require the following voltage at the feedback potentiometer to allow the A/C compressor operation in the "snowflake" or "A/C" (i.e. normal cooling mode):
Model Year Voltage
84 - 86* 3.
87 2.40 - 2.70 V
*except production from Sept. 84 to Jan. 85, requiring 4.15 - 4.30 Volts
Note: The test card supplied with test cable 201 589 09 63 00 does not include M.Y. 1987 values for checking the feedback potentianeter (test step 20). These values should be added to the card until new cards are issued.
When diagnosing complaints for no compressor operation in this mode (but does operate in maximum cooling), check the voltage at the feedback potentiometer and adjust to the higher value, if necessary.
For further information on test procedure and diagnosis of M.Y. 1987 vehicles, refer to Introduction Manual, M.Y. 1987.
Parts Information
Model Year Part Name
Part Number
84 Pushbutton control unit
201 830 03 85
85-86 Pushbutton control unit
201 830 05 85
87 Pushbutton control unit
201 830 07 85
C. New Version Feedback Potentiometer
A second version potentiometer was phased into production which uses a spring-loaded screw adjuster instead of the first version segment adjuster.
The second version can be adjusted through the glove box opening.
At present only the second version potentiometer is available as a replacement part. However, to install it on first version vehicles, the following components must also be installed:
Part Name Part
Adjustment lever 201 835 00 43
Vacuum element 201 800 08 75
Spring 005 993 93 01
Screw 000931 003000
Nut 000562 003001