http://www.eclassbenz.com/2010/02/how-to-diagnose-air-conditioning-malfunctions/


Air Conditioning Diagnosis
By admin
Published: February 10, 2010Posted in: How-To GuidesTags:
Air Conditioning Diagnosis

Introduction

The Mercedes E-class air conditioning is a complicated system of blower motors, computers, 
relays, switches, and refrigeration parts. With a system this complex, 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 quickly diagnose air conditioning problems.

To make troubleshooting easier, I’ve written a software program that will analyze the results of your 
climate control self-test. All you need to do is follow the instructions, enter the values and trouble codes, 
and (hopefully) get your diagnosis.

Skill Required
Level 1: Mirror Fogger. If you can follow simple directions and have full use of at least 10 of your 20 
(or 21, as the case may be) 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
None.

Instructions
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 72°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. 
	http://www.eclassbenz.com/2010/02/how-to-diagnose-air-conditioning-malfunctions/
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.