Test Requirements
- Ambient temperature greater than 15 °C.
- Radiator and condenser are clean (clean if necessary).
- The ribbed belt that drives the A/C compressor is OK and tensioned correctly. The belt pulley is actually driving the A/C compressor.
- All air ducts, covers and seals are OK and properly installed.
- Seal between the engine compartment, hood and plenum chamber is OK and installed correctly. Refer to Bulkhead ; (Overview - Plenum Chamber Cover) to check.
- The airflow through the dust and pollen filter is not obstructed by dirt. Refer to DUST AND POLLEN FILTER, REMOVING AND INSTALLING to check.
- The air intake for the A/C unit (in fresh air and recirculating air mode) is not obstructed by dirt or retrofitted components.
- Vehicles without glove compartment cooling: The glove compartment cooling connection is sealed on the heater and A/C unit. Refer to OVERVIEW - AIR ROUTING AND AIR DISTRIBUTION IN VEHICLE INTERIOR .
- Vehicles with glove compartment cooling: The glove compartment cooling connection is installed on the heater and A/C unit according to specification (currently not available, introduction not yet finalized). Refer to OVERVIEW - AIR ROUTING AND AIR DISTRIBUTION IN VEHICLE INTERIOR .
- The vehicle is not exposed to sunlight.
- Engine is warm: Coolant temperature is greater than 80 °C (176 °F).
- The DTC memory of the Climatronic Control Module -J255- was checked and deleted, basic setting was performed and the coding for the Climatronic Control Module -J255- was checked. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
- The adaptation of the Climatronic Control Module -J255- was checked using the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
- All instrument panel vents are open.
- Check that the air vent from the footwell vents is not blocked.
- Hood closed.
- Engine is running.
Vehicles with Manual Climate Control System:
-- Adjust the following settings on the A/C system control heads:
This illustration shows the layout of the regulators -1, 2 and 3- and the buttons -4 and 5- on a left-hand drive vehicle. The layout may be different on right-hand drive vehicles.
- Turn the regulator -1- (Front A/C Display Control Head 2 -E775-) for the fresh air blower to the maximum speed.
- Turn the regulator -2- (Front A/C Display Control Head 3 -E776-) for the temperature setting to the "cold" stop.
- Turn the regulator -3- (Front A/C Display Control Head 4 -E777-) for air distribution to "instrument panel vent".
- A/C compressor on: The indicator lamp in the A/C button (in regulator -2-) illuminates.
- Recirculating air mode on: The indicator lamp in the Fresh Air and Recirculating Air Mode Button -E781- -4- illuminates.
Vehicles with Automatic Climate Control System:
-- Adjust the following settings on the A/C system control heads:
This illustration shows the layout of the regulators -1, 2 and 3- and the buttons -4 and 5- on a left-hand drive vehicle. The layout may be different on right-hand drive vehicles.
The information in the regulators -1, 2 and 3- is only displayed when the ignition is switched on and goes out when the ignition is switched off.
- "Auto" mode on: The indicator lamp in the Auto button (in the regulator -2-) illuminates.
- Turn the regulator -2- (Front A/C Display Control Head 3 -E776-) for the temperature setting to the "cold" stop.
- Turn the regulator -3- (Front A/C Display Control Head 4 -E777-) for air distribution to "instrument panel vent".
- A/C compressor on: The indicator lamp in the A/C button (in regulator -1-) illuminates.
- Recirculating air mode on: The indicator lamp for "recirculating air mode" in the Recirculation button (in the regulator -3-) illuminates.
- Turn the regulator -1- (Front A/C Display Control Head 2 -E775-) for the fresh air blower to the maximum speed.
- Defrost mode off: The indicator lamp in the Defrost Button -E782- -4- does not come on.
The indicator lamp in the AUTO button -4- turns off when the fresh air blower speed is changed manually.
Continuation for All Vehicles:
The maximum possible fresh air blower speed depends on various ambient influences (electrical system voltage, etc.)
Functions with Engine Running:
- The Radiator Fan -V7- /Radiator Fan 2 -V177- run. The activation and speed depend on the pressure in the refrigerant circuit and the engine temperature.
Depending on the version of the Climatronic Control Module -J255-, one or both the Radiator Fan -V7- /Radiator Fan 2 -V177- are switched on only from a certain refrigerant circuit pressure (currently from a pressure of approximately 9 bar (131 psi)). The radiator fan activation is displayed in the "Read measured values" function. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function (for the Climatronic Control Module -J255- and the Engine Control Module -J623-).
Depending on the engine control module, the specified and actual speed of the Radiator Fan -V7- and Radiator Fan 2 -V177- can vary from each another. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function (for the Engine Control Module -J623-).
- The fresh air blower runs at maximum speed.
The maximum possible fresh air blower speed depends on various ambient influences (electrical system voltage, etc.)
- The A/C system goes into recirculating air mode. Approximately one minute after starting the engine, the back pressure/fresh air door is closed and the air recirculation door is opened. The fresh air blower extracts the air from the vehicle interior under the instrument panel behind the glove compartment.
If one of these requirements is not met:
-- Check the DTC memory, perform the output diagnostic test mode and read the respective measured values. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function (for the Climatronic Control Module -J255-).
Refer to COOLING OUTPUT, CHECKING, VEHICLES WITH MANUAL CLIMATE CONTROL SYSTEM
Refer to COOLING OUTPUT, CHECKING, VEHICLES WITH AUTOMATIC CLIMATE CONTROL SYSTEM