Pressures, Checking
Working on the refrigerant circuit with the A/C service station (check the pressure here) usually requires, although not necessary, the high-voltage system to be disabled.
-- Charge the vehicle battery, for example, using the Battery Charger :VAS5904 in the battery support mode to minimize the number of automatic starts during the test- and measuring procedures while the ready mode is active. Refer to Battery, Charging and the appropriate service information .
-- For testing and measurement procedures that require the ready mode to be active or the ignition to be switched on, the selector lever must be in the "P" position and the parking brake must be activated. The required tools must be placed so that they do not come into contact with any rotating components in the engine and they must also not go into the vicinity of the rotating components when the engine is running.
Also move the selector lever into position "P" and activate the parking brake for testing and measuring procedures which require the ignition to be on, but do not require the ready mode to be active.
The ready mode is displayed in the Instrument Cluster Control Module -J285- above the "power meter". Refer to Owner's Manual.
For activating and deactivating the ready mode (while doing so, note the display in the Instrument Cluster Control Module -J285-). Refer to the Owner's Manual.
-- On vehicles with a high-voltage system, switch off (deactivate) the "auxiliary climate control" function. Refer to the Owner's Manual and Infotainment/MMI Operating Manual.
-- Switch off the ignition.
-- Connect the A/C service station. Refer to A/C SERVICE STATION ON REFRIGERANT CIRCUIT, CONNECTING .
Is a concern occurs on only on evaporator, on vehicles with two evaporators (a evaporator in the heater and A/C unit and an evaporator on the high-voltage battery heat exchanger) check the pressure in the refrigerant circuit, is this okay? Check the line connection between the evaporator in question and the exit of line connection at distribution point of refrigerant lines (for constriction). If no malfunction can be detected, discharge the refrigerant circuit and charge it with the specified refrigerant quantity. Then check the pressure and the A/C system cooling output again, if the concern is present again check/replace the following components: If the concern only occurs on the evaporator in the heater and A/C unit, check the shut-off valve in from of the evaporator in the heater and A/C unit (it is not open in the activated state and lets the refrigerant flow through). Replace the expansion valve on the evaporator in the heater and A/C unit id no malfunction can be determined on the shut-off valve. If there is a concern only on the evaporator on the high-voltage battery heat exchanger, check the activation of the shut-off valve on the expansion valve on the evaporator and high-voltage battery heat exchanger (it is not closed in the activated state and does not let refrigerant flow through). Refer to Refrigerant Circuit .
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 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 .
The switching pressures for the activation of the Electrical A/C Compressor -V470- and the Radiator Fan -V7- are vehicle-specific. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function for the A/C system and the battery regulation.
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.
- Charge the vehicle battery, for example, using the Battery Charger :VAS5904 in the battery support mode to minimize the number of automatic starts during the test- and measuring procedures while the ready mode is active. Refer to Battery, Charging and the appropriate service information .
-- Activate the ready mode (the engine must run). Refer to the Owner's Manual.
-- Adjust the A/C system to maximum cooling output. Refer to COOLING OUTPUT, CHECKING .
- The Electrical A/C Compressor -V470- is activated and runs. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function for the A/C system and the battery regulation. Refer to Refrigerant Circuit .
The activation of the electrically driven A/C compressor occurs from the vehicle electrical system. The engine speed does not have any effect on the A/C cooling output.
The A/C compressor is currently not actuated at the maximum specified speed (of approximately 8500/min) on a stationary or slow moving vehicle (up to a speed of approximately 45 km/h (28 mph)) (the A/C compressor speed is limited to approximately 5000/min).
The activation of the electrically driven A/C compressor can be monitored by the Guided Fault Finding using the Vehicle Diagnostic Tester in the"Guided Fault Finding" Function for A/C System and the Battery Regulation.
All of the test requirements marked with a * are vehicle-specific and described in the Service Information for the vehicle. Refer to COOLING OUTPUT, CHECKING .
If the A/C compressor is not activated while ready mode is active:
-- 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 and the battery regulation.
- The radiator and condenser are clean (if necessary clean)*. Refer to Refrigerant Circuit and RADIATOR/RADIATOR FAN .
- The heat shield insulation on the expansion valve is OK and installed correctly*. Refer to Refrigerant Circuit .
- All air guides, covers and seals are OK and correctly installed*. Refer to Component Location Overview - A/C System .
- The diagnostic of the A/C system does not determine a malfunction (with the ready mode active and the A/C system switched on) in the measured value block no compressor shut-off condition is shown. Using the Vehicle Diagnostic Tester in the"Guided Fault Finding" function for the A/C system and the battery regulation.
- 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. Refer to Component Location Overview - A/C System . If no errors can be detected, evacuate the refrigerant.
- The airflow through the dust and pollen filter is not impaired by debris*. Refer to Component Location Overview - A/C System .
- The heater and A/C unit does not draw in any secondary air at the highest fresh air blower speed. Evaporator and heater not drawing in secondary air at maximum fresh-air blower speed. *Refer to COOLING OUTPUT, CHECKING .
- 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 .
- Fresh-air intake ducts beneath hood and in passenger compartment as well as corresponding water drain valves OK*. Refer to Component Location Overview - A/C System .
- Vehicle is not exposed to direct sunlight. Refer to COOLING OUTPUT, CHECKING .
- The ambient temperature is greater than 15 °C (59 °F).
- All instrument panel vents are open *.
Adjustment for example on the Front A/C Display Control Head -E87- (and the Rear A/C Display Control Head -E265- on vehicles with two heater and A/C units) *. Refer to COOLING OUTPUT, CHECKING and Component Location Overview - A/C System .
Adjustment for example on the Front A/C Display Control Head -E87- *:
-- 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 and RADIATOR/RADIATOR FAN .
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 and the battery regulation.
- 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.* Refer to COOLING OUTPUT, CHECKING and Component Location Overview - A/C System .
- The pump/valve unit valves are closed and there is no coolant circulation pump delivery.* Refer to COOLING OUTPUT, CHECKING and Component Location Overview - A/C System .
The activation of the electrically-driven A/C compressor takes place from the vehicle electrical system, the engine speed does not have an influence on the A/C system cooling output. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function of the A/C system and the battery regulation.
The A/C compressor is currently not actuated at the maximum specified speed (of approximately 8500/min) on a stationary or slow moving vehicle (up to a speed of approximately 45 km/h (28 mph)) (the A/C compressor speed is limited to approximately 5000/min).
The activation of the electrically driven A/C compressor can be monitored by the Guided Fault Finding using the Vehicle Diagnostic Tester in the"Guided Fault Finding" Function for A/C System and the Battery Regulation.
Pressures must be measured at the service connections; the component location for these connections are vehicle-specific. Refer to Refrigerant Circuit .
Specified Values for the Refrigerant Circuit Pressures
- Refrigerant Circuit Pressures Specified Values, Vehicles without Heat Pump. Refer to Refrigerant Circuit Pressures Specified Values, Vehicles without Heat Pump .
- Refrigerant Circuit Pressures Specified Values, Vehicles with Heat Pump. Refer to Refrigerant Circuit Pressures Specified Values, Vehicles with Heat Pump .
The specified and current speed for the activation of the Electrical A/C Compressor -V470- and the Radiator Fan -V7- are vehicle-specific. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function for the A/C system and the battery regulation.
Pressures must be measured at the service connections; the component location for these connections are vehicle-specific. Refer to Refrigerant Circuit .