Test Requirements

• Radiator and condenser are clean (clean if necessary).
• The thermal insulation at expansion valve is OK and properly installed.*
• Ribbed belt is OK and properly tensioned. Ribbed belt for A/C compressor and generator are OK and correctly tensioned.*
• All air ducts, covers and seals are OK and properly installed.
• Fault finding on the electrical equipment and vacuum system found no malfunction.* Use the Vehicle Diagnostic Tester("OBD" function or "Guided Fault Finding" for the A/C system) and refer to Refrigerant Circuit (vehicle-specific Service Information).

• The A/C system OBD does not detect any malfunctions (when the engine is running and the A/C system is switched on), and no compressor shut-off condition is displayed in the measured value block (only for vehicles with "A/C system" OBD). Use the Vehicle Diagnostic Tester("OBD" function or "Guided Fault Finding" for the A/C system) and refer to Refrigerant Circuit (vehicle-specific Service Information).
• The various pressure/temperature sensors installed on or in the refrigerant circuit provide valid measured values when the A/C system is being used. To check, use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function and refer to Component Location Overview - A/C System . If no errors can be detected, evacuate the refrigerant.

• Air flow through dust and pollen filter not obstructed by dirt*
• The A/C unit not drawing in secondary air at maximum fresh air blower speed* Evaporator and heater not drawing in secondary air at maximum fresh-air blower speed*
• Air guide doors in the A/C unit, heater and evaporator reach their end position*
• Fresh-air intake ducts beneath hood and in passenger compartment as well as corresponding water drain valves OK*. Refer to Air Routing (vehicle-specific Service Information).

• The engine is warm.
• Vehicle is not exposed to direct sunlight. Refer to COOLING OUTPUT, CHECKING (vehicle-specific Service Information).

• The ambient temperature is greater than 15 °C (59 °F).
• All instrument panel vents are open.

-- Start the engine.

Settings on the A/C system control module, for example on the Front A/C Display Control Head -E87- or the Climatronic Control Module -J255- (and Rear A/C Display Control Head -E265- for vehicles with two A/C units):

-- Preselect "Auto" mode (A/C compressor on).

-- Set temperature preset to "LO" on the driver and front passenger side (and the rear passenger compartment, left and right side in vehicles with two A/C units).

Setting on heater controls:

-- Press A/C button and rec- or recirculation button.

-- Turn temperature knob towards "cold" stop.

-- Set the fresh-air blower dial to position "4".

The following system test conditions should be met:

• One or more Radiator Fan -V7- (Radiator Fan 2 -V177-) operated (at least speed 1)*

• Fresh Air Blower -V2- (and Rear Fresh Air Blower -V80- in vehicles with two A/C units) running at maximum speed.
• Recirculated/fresh air door set to "Recirculated air mode" (within one minute, after starting vehicle, air-flow door is closed and recirculated-air door is opened)*
• The coolant shut-off valve is closed.*
• The valves of pump valve unit are closed and there is no coolant circulation pump delivery.*
• Compressor is actually driven (A/C Clutch -N25- operated, overload safeguard (if installed) not tripped).*