Mercedes Benz 107 AC / Heat System Trouble Shooting

 Got Heat or AC System Problems ?

Mercedes 107 Heat System / AC Problems and Remedies

There are a number of reasons that the heat system, air conditioning and climate control fail or just don't work well on the Mercedes 107 series models, while there are multiple issues that occur to create these problems, there are some affordable solutions to their repair and here are some main reasons and their solutions.

#1 Climate Control Servo Unit. During the Seventies, German cars were not noted for their effective air conditioners, and these SLs are no exception. Except for the servo units in the automatic climate-control systems of the 1977-1980 450SLs, which seem to fail every three years, the air conditioners don't break particularly often. "They just don't cool well".

Has your 1976 to 1984 Mercedes' Climate Control System stopped functioning?

For example: when you try to select blower / air conditioning... is heat all you can get? ...no air? In fact, no matter how you set the controls... you can't any-longer actually turn-off the heat? The most likely problem: Your vehicle has a defective climate control servo. (To verify your servos' proper function, while you place your ear as close to the unit as possible so as to listen to how it reacts when it receives power, simply have someone turn the ignition switch (key) to the accessory position. Immediately as the accessory position is engaged, you should easily be able to hear a "whirring sound" coming from within the servo unit - which sound results from the small motor which powers the unit turning gears inside of it...like a clock. If no such sound can be heard: your servo is defective.

Replacing the Servo can be expensive...up to $1,200.00 for a new unit and from $350.00 and up for a rebuilt one. And you know what?  Believe it or not, with the use of a few simple tools, ( a 3/8" spanner and a screw driver) in under 1 hour, you yourself can actually easily fix this problem...That is, you can simply remove your defective servo and replace it with one that functions.

Important Note: The old servo units are made of plastic that cracks causing them to fail, look for newer aluminum body units with a 2 year + warranty, core charge may apply. One place to get aftermarket aluminum units is at German Star  for $465.

Servo Replacement Alternative. 1977 to 1980 Climate Control Servo Bypass Conversion Kit For use to convert 1977 to 1980 automatic climate control servo to a manual system. If your heat has failed again and you do not want to spend another $400-600 for a climate control servo and amplifier maybe it is time to just convert to a manual system. It will not be as nice as the original automatic system, but at least you will have heat when you need it. This kit comes with a new manual control valve, hose section, splice fitting, four German hose clamps, a 5 foot control cable and complete instructions on how to properly install this kit yourself.

#2 Blower Motor Issues. If your blower motor has been intermittent or some days it just will not come on until you drive for a while, or not at all, your motor contact brushes are most likely at the end of their life. At an age of 15 years old or more heater motor brushes are very prone to failing at any time from wear and age. This is something you may just want to replace as a preventative measure. If they have not failed yet they most likely will sometime soon. Repair Broken Heater Box

Brush Replacement Guide   Order Brushes

#3 Center Vents Don't Open or Stay Open. If you own a late-model 107 that uses vacuum actuators to operate the air distribution flaps, then you have probably experienced loss of function of the center vents (among other air distribution problems). Reports have been shared of fixes ranging from "propping open the center vent" to plugging vacuum lines to allow air circulation from the vents. While the most common cause for loss of function may be degraded and failed vacuum pod diaphram's, other causes do exist and can be more onerous. The following pages and pictures are offered to shed some illumination on the subject of "why do my center vents not open/stay open?"

Vacuum Elements Repair and Replacement

Mercedes Vacuum System Troubleshooting and Repair Basics