BMW and Mercedes are known for their engineering, but even the best vehicles still need repairs, and sometimes parts fail. The A/C and HVAC systems seem one area most prone to failure, not just on German cars, but all cars. With so many wires, sensors, actuators, flaps, and vacuum motors, it’s amazing they last as long as they do. The sad part is there is little you can do to maintain the system to prevent the need for repairs.
In most cases you have two main types of failures in the HVAC system. The first is misdirected air flow from the vents, or drastic temperature differences from the vents. In this instance, the likely culprits are the “flaps” or “doors” that control the air flow and direction are malfunctioning.
The second most common HVAC problem is the car simply doesn’t cool like it used to or the air blows hot from the vents. This is typically caused by loss of refrigerant in the system from a leak, or a compressor that has given out. A compressor that has failed is a very straight forward repair. However, a leak in the system can be tough to track down.
Standard procedure to diagnosis a loss of refrigerant involves recharging the system with a UV dye and then using a black light to inspect all the seals, hoses, compressor, and other parts. The UV dye will clearly show the point of the leak. In the extreme case, the leak will be tracked down to the A/C evaporator.
Replacement of the evaporator is no easy task and on most BMW and Mercedes, they are located behind the dashboard against the firewall. Gaining access to the evaporator involves removing almost everything you see in front of you, the dashboard, center console, steering wheel, glove box, and air bags. The interior of the car is basically stripped down to the firewall.
You can see from the pictures below, this is a major repair! However, with our experience and knowledge this repair can be made a little less painful than going to the stealership……I mean dealership.