Is your cooling fan running at full speed constantly? This is a prevalent fault on Mercedes-Benz W204, W207, and W212 models. Typically, this is a "no code fault," meaning that the check engine light isn't illuminated and there are no codes stored in the ECU. On these models, this is often the result of a faulty A/C pressure switch reporting an implausible value or an excessively high value.
Before jumping into this project, you're going to want to use an OBDII scan tool to verify the value the system is receiving from the sensor. You can find this value in various modules; however, I would recommend reviewing live data in the front SAM (Signal Acquisition Module).
Once you have verified your pressure switch is at fault, you will need to have your A/C system evacuated of refrigerant before you can replace it. It is illegal to vent refrigerant into the atmosphere as it's extremely harmful to the environment. We had our system evacuated at a local shop to demonstrate this procedure.
- Mercedes C300 2008-2014
- Mercedes C350 2008-2015
- Mercedes E350 2010-2016
Tools needed to complete this repair:
Parts needed to complete this repair:
Step 1: Lift your car and remove splash shields
The pressure switch is located directly under the A/C condenser so you will want to start the procedure by lifting the vehicle and removing the forward bumper splash shield. This will allow you to access the shield that protects the condenser and the A/C pressure switch. Fold the second splash shield out of the way to gain access to the A/C pressure switch.
Step 2: Remove old A/C pressure switch and replace
This step is straight forward and just requires you to be careful. A/C lines are typically constructed of aluminum and can break easily, so you want to hold the line while using your 27mm box wrench to remove the sensor.
When reinstalling the new A/C pressure switch, lubricate the O-ring and thread it into the A/C line. Since you're working with aluminum, be sure to use a torque wrench and torque to 17ft⋅lb.
Writer/Editor at FCP Euro and owner of a daily R53 MINI Cooper, a track-built R53 MINI, and a 1997 Dakar Yellow E36 M3 Sedan. ••• Instagram: @evan.madore