Vehicle presented with a loss of refrigerant, the standard evacuation of the A/C was preformed and no gross (large) leaks were detected. Our service protocol is always recharge the air conditioning (A/C) systems with a UV test dye during any A/C service. Since the refrigerant is a gas, it is very near impossible to visually witness the leakage, other than perhaps refrigerant oil staining. The UV dye clearly shows the point of leakage, be it a hose, seal, compressor or other part. One of the most challenging components of the A/C system to diagnose is the evaporator core, located inside the dash of the car itself. As the A/C evaprorotr core is not readily visible, except by much dissembly of the dash itself, we use a three point diagnosis on these, the first part is confirming the loss of refrigerant, second, we inspect all visible components of the A/C system to eliminate any external parts, finally we inspect the drain pipes for the evaporator core, looking for telltale evidence of the UV test dye to present in the condensation run off.
Replacement of the air conditioning (A/C) evaporator core is no easy task on any car, yet alone a vehicle as complex and well engineered as a Mercedes Benz. Access to the core involves removing the center console, complete dash, steering wheel, airbag, radio, climate control head and basically stripping the car down to the engine firewall. You can see by the photos that this is no easy task. If the diagnosis is done correctly, you’ll see the evaporator core stained with the dye.
While servicing this car, we were able to help the customer with another problem, saving considerable labor time. Hiding in the dash of that nice C-Class is a small plastic lever, which, given time and use, may fracture, resulting in a noise from the dash area. The noise is noted as a “snapping” or “popping” sound in or near the center vents, and the customer may also have a concern about incorrect temp or air flow from the vents. The problem, a small plastic lever which operates the foot well flaps via a servo motor.
Running a diagnostic with the Mercedes SDS computer should confirm the fault, before the teardown and visual inspection. The plastic lever in question has been redesigned to be more robust, and the update kit is available from Mercedes. The service correction is quite involved, requiring removal of the center console upper panel, radio, climate control head, and lover dash with the glove box. Once the arm is located and replaced, the SDS should be used to run a “normalization” routine on the flap system.