W210 Air Conditioning Diagnosis

W210 Air Conditioning Diagnosis


It’s likely that you’ll encounter an air conditioning problem at some point during your ownership. Thankfully, the onboard climate control computer has a self-check mode that can help you diagnose the problem.

Skill Required

Level 1: Minimal. If you can follow simple directions and have full use of at least 10 of your 20 digits, you can do this job. Too busy? Delegate this project to your 11 year-old. Just make sure he doesn’t drive the car through the living room wall.

Tools Required

Pen and paper.

Parts Required



Part 1 — Collect Sensor Data

First we’ll get the values of all the various climate control sensors. These sensors constantly monitor data like air temperature, refrigerant pressure, etc. Odds are if something’s wrong, a sensor will pick it up. Let’s get started!

Start your car.

Press the “AUTO” button on your climate control.

Turn on the A/C (i.e. “EC” light must be off; if the light won’t shut off, continue with this test. We’ll address your “EC” light on the next page.)

Let the car idle for about 3 minutes.

Set the temperature on each side to 68°F. You can do this quickly by pressing both the red and blue arrows simultaneously.

Press and hold the “REST” button for five seconds or until the left side of the display says “01.” The left side indicates which sensor you’re checking. In this case, #1 is the in-car temperature sensor. The right side of the display shows the value of sensor #1 (in this case, the actual in-car temperature).

Press the “AUTO” button on the left side to move to the next sensor. Press the “AUTO” button on the right side to move to the previous sensor.

Record the ID number of each sensor (left side of display) and its corresponding value (right side of display). For example, in the picture on the right, you would record that sensor #5 has a value of 6.

You only need to do this for sensors #1-8. You can write down the values for the other sensors, but they’re not really related to air conditioning function.

When you are done, press the “REST” button again to exit the self-check mode.

Part 2 — Collect Trouble Codes

Now that we have all the sensor values, let’s check the computer for malfunction codes. Read this carefully, because you have a 20 second window after switching on the ignition to load the trouble code display mode.

Ignition must be switched on. 20 second timer starts.

Increase the left side temperature (left red arrow) until left side says “HI.”

Decrease the right side temperature (right cold arrow) until right side says “LO.”

If your 20 seconds passed, switch off the ignition and switch it back on. Your HI/LO settings will be preset. Timer restarts.

Press and hold the “EC” and “REST” buttons simultaneously for at least five seconds.

The screen will go blank.

Load the first code by pressing the right side “AUTO” button.

If you have any error codes in memory, the screen should look like the figure on the right. The ‘E’ stands for “error.” In this case, we have error code B1234.

Write down each error code. To cycle through the codes, press the right side “AUTO” button.

When you finish, press the “REST” button to exit.

Part 3 — Send Me Your Sensor Values & Trouble Codes

Use the comments box below to provide background info on the problem, sensor values, and error codes.  I’ll take a look at them personally.  I can’t guarantee that I’ll know the answer to your problem, but I’ll give it my best shot.   If you note your e-mail address you’ll get a copy of my reply by e-mail.   Please note:  I am still doing this service.   The comments software now defaults to showing older questions/replies first.   But you can change it show the newest first by clicking on the drop-down menu button below the comments box.  If you don’t hear anything within a few days, please contact me!  Every now and then a question falls through the cracks.

Part 4 — Buy Me a Beer

I’m a Mercedes enthusiast, and I enjoy helping others out.  I may save you hundreds of dollars.  Although it is certainly not required, I always appreciate a “thank you” in the form of a nice, cold beer.  (During the summer months, the volume can be overwhelming.  Please understand that I have to prioritize those who make a contribution.)

If you’d like to buy me a beer (or a nice bottle of wine), click on the button below: