Test Prerequisites

• Radiator and condenser are clean (clean if necessary)
• Thermal insulation at expansion valve 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 OK and properly installed
• Fault Finding did not detect any faults in the electrical system or in the vacuum system.* Refer to the Vehicle Diagnostic Tester("OBD" or "Guided Fault Finding for the A/C system") and Diagnosis and Testing (vehicle-specific repair information).

• Air conditioner On Board Diagnostic (OBD) has not revealed any faults (with engine running and air conditioner switched on), no compressor shutoff criterion displayed in measured value block (vehicles with Air conditioner On Board Diagnostic only)* Refer to the Vehicle Diagnostic Tester("OBD" or "Guided Fault Finding for the A/C system") and Diagnosis and Testing (vehicle-specific repair information).

• Air flow through dust and pollen filter not obstructed by dirt*
• Air conditioner 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 doors in air conditioner unit, heater and evaporator reach end position*
• Fresh-air intake ducts beneath hood and in passenger compartment as well as corresponding water drain valves OK*. Refer to Diagnosis and Testing (vehicle-specific repair information).

• Engine is warm
• Vehicle not exposed to direct sunlight. Refer to Refer to Diagnosis and Testing (vehicle-specific repair information).

• Ambient temperature greater than 15° C (59 °F)
• All instrument panel vents open

-- Start the engine.

Adjustment at Front A/C display control head -E87- or Climatronic Control Module -J255- (and Rear A/C display control head -E265- in vehicles with two A/C units):

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

-- Set temperature pre-selector switch to LO for driver's side and front passenger's side (and left and right rear seats in vehicles with two A/C units).

Setting on heater controls:

-- Press A/C button and Rec- or recirculated air button.

-- Turn rotary temperature control towards cold stop.

-- Set rotary fresh-air blower control to 4.

The following system test conditions should be met:

• One or more Radiator fan -V7- 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 1 minute, after starting vehicle, air-flow door is closed and recirculated-air door opened)*
• The coolant shut-off valve closed.*
• Valves of pump valve unit closed and no coolant circulation pump delivery*
• Compressor is actually driven (A/C clutch -N25- operated, overload safeguard (if installed) not tripped)*