Test Requirements
- The A/C service station in connected to the refrigerant circuit. Refer to A/C SERVICE STATION ON REFRIGERANT CIRCUIT, CONNECTING .
- Pay attention to the test requirements for checking the pressures in the refrigerant circuit with the ignition switched off. Refer to REFRIGERANT CIRCUIT WITH IGNITION SWITCHED ON, CHECKING PRESSURE - Test Requirements .
- The pressures in the refrigerant circuit with the ignition turned off meet the specifications. Refer to REFRIGERANT CIRCUIT WITH IGNITION SWITCHED ON, CHECKING PRESSURE .
- Pay attention to the test requirements for checking the cooling output. Refer to COOLING OUTPUT, CHECKING (CABRIOLET) .
The switching pressures for the activation of the A/C Compressor Regulator Valve -N280-, the A/C Clutch -N25- (if equipped) and the Radiator Fan -V7- are vehicle specific. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
Pressures must be measured at the service connections; the component location for these connections are vehicle-specific. Refer to REFRIGERANT CIRCUIT .
- The engine is warm (at an ambient temperature below 25 °C (77 °F)).
If the engine is not warm perform a road test.
For the cooling output test the engine must be warm but at an ambient temperature smaller than 25 °C (77 °F) a specific A/C system cooling output it is necessary that the engine and lower ambient temperatures are warm.
-- Start the engine.
-- Adjust the A/C system to maximum cooling output. Refer to COOLING OUTPUT, CHECKING (CABRIOLET) .
- The A/C compressor is actually being driven with the engine running (visual inspection). Refer to REFRIGERANT CIRCUIT .
- The A/C Compressor Regulator Valve -N280- is activated. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function for the A/C system.
The A/C compressor is driven by different components depending on the engine (belt or input shaft). The belt pulley or the drive unit has an overload protection to protect these components and the engine, if the A/C compressor is runs with resistance. Refer to A/C COMPRESSOR .
On vehicles with A/C Compressor Regulator Valve -N280- the control current can be read out in the measured values. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function for the A/C system.
If A/C compressor is not driven with the engine running or regulating valve is not actuated:
-- Determine and eliminate cause for example by checking air conditioner DTC memory. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
-- If equipped, check the power supply for the A/C Clutch -N25- if this is OK, service the A/C clutch. Refer to REFRIGERANT CIRCUIT .
-- Check the activation of the A/C Compressor Regulator Valve -N280-. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
On A/C compressors with a A/C Clutch -N25- the A/C compressor only works (delivers refrigerant) when near the A/C Compressor Regulator Valve -N280- the A/C Clutch -N25- is also activated. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
The A/C Compressor Regulator Valve -N280- (and the A/C Clutch -N25-) is activated by the A/C Control Module -J301-, from the Front A/C Display Control Head -E87- or the Climatronic Control Module -J255- or a downstream control module. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system. Refer to REFRIGERANT CIRCUIT .
All of the test requirements marked with a * are vehicle-specific and described in the repair information belonging to the vehicle. Refer to COOLING OUTPUT, CHECKING (CABRIOLET) (vehicle-specific repair information) and REFRIGERANT CIRCUIT .
- Radiator and condenser are clean (if necessary clean)*. Refer to REFRIGERANT CIRCUIT .
- The heat shield insulation on the expansion valve is OK and installed correctly*. Refer to REFRIGERANT CIRCUIT .
- Ribbed belt is OK and properly tensioned. Ribbed belt for A/C compressor and generator are OK and correctly tensioned.* Refer to REFRIGERANT CIRCUIT (vehicle-specific repair information) and REFRIGERANT CIRCUIT .
- The drive unit and the A/C compressor is OK and installed correctly.* Refer to REFRIGERANT CIRCUIT (vehicle-specific repair information) and REFRIGERANT CIRCUIT .
- All air guides, covers and seals are OK and correctly installed*. Refer to AIR GUIDE .
- The A/C system diagnostic 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 values of the corresponding control module (only for vehicles with "A/C system" diagnostic).* Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function for the A/C system.
- Air flow through dust and pollen filter not obstructed by dirt* Refer to AIR GUIDE .
- The heater and A/C unit does not draw in any secondary air at the highest fresh air blower speed. The evaporator and the heater not drawing in secondary air at maximum fresh-air blower speed.* Refer to AIR GUIDE .
- The air doors in the heater and A/C unit, in the heater and in the evaporator reach their end position.* Refer to COOLING OUTPUT, CHECKING (CABRIOLET) (vehicle-specific repair information) and AIR GUIDE .
- The fresh air intake ducts under the hood and in the vehicle interior and the corresponding water drain valves are OK.* Refer to COOLING OUTPUT, CHECKING (CABRIOLET) (vehicle-specific repair information) and AIR GUIDE .
- The engine is warm.
- Vehicle is not exposed to direct sunlight. Refer to COOLING OUTPUT, CHECKING (CABRIOLET) .
- The ambient temperature is greater than 15 °C (59 °F).
- All instrument panel vents are open.* Refer to AIR GUIDE .
Adjustment for example on the Front A/C Display Control Head -E87- or the Climatronic Control Module -J255- or the A/C Control Module -J301- (and the Rear A/C Display Control Head -E265- on vehicles with two heater and A/C units)*. Refer to COOLING OUTPUT, CHECKING (CABRIOLET) (vehicle-specific repair information) and AIR GUIDE .
Adjustment on the Front A/C Display Control Head -E87- /Climatronic Control Module -J255- *. Refer to COOLING OUTPUT, CHECKING (CABRIOLET) (vehicle-specific repair information) and AIR GUIDE .
-- Preselect "Auto" mode (A/C compressor on).
-- Set temperature pre-selector switch to "cold" or "LO" for driver's side and front passenger's side (and left and right rear seats in vehicles with two heater and A/C units).
Adjustment on the A/C Control Module -J301- *:
-- Press A/C button and Rec- or recirculated air button.
-- Turn rotary temperature control towards "cold" stop.
-- Position the fresh-air blower dial in the position "4" (maximum fresh air blower speed).
The following system test conditions should be met:
- The Radiator Fan -V7- is operated or the Radiator Fan -V7- and Radiator Fan 2 -V177- runs (minimum in 1 step).* Refer to COOLING OUTPUT, CHECKING (CABRIOLET) (vehicle-specific repair information) and AIR GUIDE .
On specific versions the fan is switched on after the refrigerant circuit pressure specified value is exceeded. Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function of the A/C system.
- Fresh Air Blower -V2- (and Rear Fresh Air Blower -V80- in vehicles with two heater and A/C units) running at maximum speed.*
- The coolant shut-off valve is closed.* Refer to COOLING OUTPUT, CHECKING (CABRIOLET) (vehicle-specific repair information) and AIR GUIDE .
- The pump/valve unit valves are closed and there is no coolant circulation pump delivery.* Refer to COOLING OUTPUT, CHECKING (CABRIOLET) (vehicle-specific repair information) and AIR GUIDE .
- Fresh Air Blower -V2- (and Rear Fresh Air Blower -V80- in vehicles with two heater and 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.*