Cooling Output, Checking
Cooling Output, Checking
The cooling output test requirements are fulfilled. Refer to=> [ Cooling Performance Test Requirements ] Initial Inspection and Diagnostic Overview.
- Measure ambient temperature must be greater than 15 °C.
- Close doors, hood, windows and sun roof.
- Open all dash panel vents.
- Switch ignition on.
- Select the "Econ" operating mode on the MMI A/C mode off.
- Close vents in "B" pillar.
- Set handwheel for variable temperature center vent to "Warm ".
- Start the engine.
- Initiate a Guided Fault Finding on the A/C system vehicle diagnosis testing and information system VAS 5051 in the "Guided Fault Finding" function.
- In the "Read measured value block" function, select the display group with the following values (A/C Compressor Regulator Valve (N280) activation and High Pressure Sensor (G65) measured value block and check the display vehicle diagnosis testing and information system VAS 5051 in the "Guided Fault Finding" function.
• The compressor activation via the A/C Compressor Regulator Valve (N280) is switched off the compressor is switched off and 0% is shown in the display field.
• The pressure in the refrigerant circuit determined by the High Pressure Sensor (G65) is the same or greater than the value in the table at the measured ambient temperature.
• In terms of absolute pressure, 0 bar corresponds to an absolute vacuum. Normal ambient pressure equals approximately 1 bar absolute pressure. On the scales of most pressure gauges, 0 bar corresponds to an absolute pressure of one bar can be seen from -1 mark below 0.
• Pressure in refrigerant circuit is governed by ambient temperature. On account of heat given off by components radiator, pressure displayed with warm engine will be slightly higher than that given for the respective ambient temperature.
If the displayed pressure in the refrigerant circuit is lower than in the table:
- Check signal of High Pressure Sensor (G65). Refer to => [ High Pressure Sensor, Checking Signal ] High Pressure Sensor, Checking Signal
- If no malfunction is found in the High Pressure Sensor (G65), there is not enough refrigerant in the circuit Transfer the vehicle to a workshop that has the necessary equipment and trained personnel => Refrigerant R134a - Servicing.
If pressure in refrigerant circuit is OK:
- Switch on compressor, select "Auto" mode on front A/C control head Climatronic Control Module (J255) or on MMI (Multi Media Interface) to do so.
- Select temperature preselect for driver's and front passenger's side to "Lo" on front A/C control head Climatronic Control Module (J255).
- Set direction of air flow to "instrument panel vents" on front A/C control head Climatronic Control Module (J255).
- Select "read measured values block"vehicle diagnosis testing and information system VAS 5051 in the "Guided Fault Finding" function.
- Check the indicators in the various display fields on the tester display:
- A duty cycle greater than 30% is shown in the display field for the A/C Compressor Regulator Valve (N280) activation the (N280) is activated, the compressor is switched on.
- Current greater than 0.3 A is shown in the display field for the current to the A/C Compressor Regulator Valve (N280) the current flows via the (N280), the compressor is switched on.
- The pressured measured by the High Pressure Sensor (G65) and display increases over the value with the compressor switched off.
• A/C Compressor Regulator Valve (N280) is activated by front A/C control head Climatronic Control Module (J255) such that temperature of air downstream of evaporator reaches specified value approximately 2 to 5 °C.
• After starting vehicle, value greater than 75 % (0.55A) is displayed depending on measured temperature, engine speed and electrical system voltage.
• As soon as the temperature measured by Evaporator Vent Temperature Sensor (G263) nears the specified value, the activation, and thus the compressor output, is reduced.
• The connector to A/C Compressor Regulator Valve (N280) and the connector to the electric engine mounts are identical in construction. If connectors are interchanged possible on vehicles with 4.2 l engine, no entry is made in DTC memory, however since the compressor is continuously actuated, the evaporator may ice up.
• If no voltage or voltage that is too low is shown in the display field with the values for the A/C Compressor Regulator Valve (N280) activation, check the (N280) activation. Refer to => [ A/C Compressor Regulator Valve, Checking Activation Signal ] Testing and Inspection.
• If the pressure in the display field with the High Pressure Sensor (G65) measured value does not change and the compressor activation is OK, check if the A/C Compressor Regulator Valve (N280) is actually activation and if the compressor is actually driven. An overload protection is installed between the compressor and the belt pulley/drive unit. The compressor will not be driven if it has been triggered. If no malfunction is found, there is a malfunction in the refrigerant circuit. Transfer the vehicle to a workshop that has the necessary equipment and trained personnel to perform the work => Refrigerant R134a - Servicing. Notify the workshop about the malfunction.
- Press button for recirculating-air mode on front A/C control head Climatronic Control Module (J255) symbol for " recirculating-air mode" lights up in button.
- Set engine speed of 2000 rpm start of time measurement.
- Select the display group with the Evaporator Vent Temperature Sensor (G263) in the "Read measured values block " function vehicle diagnosis testing and information system VAS 5051 in the "Guided Fault Finding" function.
- Compare the displayed measure value for the Evaporator Vent Temperature Sensor (G263) in the display field with the values in the diagram.
A Measured air temperature of Evaporator Vent Temperature Sensor (G263)
B Ambient temperature
C Permissible tolerance range
Depending on ambient temperature, air temperature measured must be within stated tolerance range after 5 minutes.
• If the required values are not met, check the Evaporator Vent Temperature Sensor (G263) measured value and compare the display measured values for the sensor with those for the Left Vent Temperature Sensor (G150) and Right Vent Temperature Sensor (G151).
- The measured values for the Left Vent Temperature Sensor (G150) and Right Vent Temperature Sensor (G151) only differ slightly from the measured value for the Evaporator Vent Temperature Sensor (G263). Perform the procedure for identifying malfunctions if specified values are not reached. Refer to => [ Determining Malfunction if Specified Values Are Not Obtained ] Determining Malfunction if Specified Values Are Not Obtained.
- If the measured value for the Evaporator Vent Temperature Sensor (G263) is greater than the measured value for Left Vent Temperature Sensor (G150) and Right Vent Temperature Sensor (G151), make sure the Evaporator Vent Temperature Sensor (G263) is installed correctly and perform an electrical test for this sensor. Refer to=> [ Evaporator Vent ] Service and Repair and vehicle diagnosis testing and information system VAS 5051 in the "Guided Fault Finding" function.
• The function of the air conditioning is recognizable, the refrigerant pipe on the low pressure side, thick line, cools off.
If measuring value of Evaporator Vent Temperature Sensor (G263) and therefore cooling performance of A/C system is OK.
- Compare the measured value for the Evaporator Vent Temperature Sensor (G263) with the measured values for the Left Vent Temperature Sensor (G150) and Right Vent Temperature Sensor (G151).
- The center outlet temperature sensor (G150) and footwell outlet temperature sensor (G151) measured values may not be greater than maximum 3° after 5 minutes, than the evaporator vent temperature sensor (G263) measured value.
- If the measured value for the Evaporator Vent Temperature Sensor (G263) is OK and the measured value for the Left Vent Temperature Sensor (G150) and/or Right Vent Temperature Sensor (G151) is more than 3°C greater than the one for the (G263), perform the procedure for determining the malfunction when there is a temperature increase after the evaporator. Refer to => [ Temperature Increase Downstream from Evaporator, Determining Malfunction ] Temperature Increase Downstream from Evaporator, Determining Malfunction.
If the required values are not reached, compare the displayed measured values for the (G150) and (G151) with each other.
• If the measured values for the (G150) and (G151) are OK, check the activation and function of the Left Heat Regulating Valve (N175) and Right Heat Regulating Valve (N176) and the Coolant Pump (V50). Refer to => [ Ventilation System Heat Output and Pump Valve Unit Function ] Ventilation System Heat Output and Pump Valve Unit Function and vehicle diagnosis testing and information system VAS 5051 in the "Guided Fault Finding" function.
• If the measured value for one of the sensors the (G150) or (G151)) is lower than the measured value for the (G263): Make sure the (G263), (G150) and (G151) are installed correctly and check their electrical connectors for contact resistance. Replace the faulty sensor if necessary vehicle diagnosis testing and information system VAS 5051 in the "Guided Fault Finding" function.
• Temperature of air flowing out of "center" instrument panel vents can also be measured using a standard thermometer.
• If no malfunction is found in the Left Vent Temperature Sensor (G150), the Right Vent Temperature Sensor (G151), the Left Heat Regulating Valve (N175), the Right Heat Regulating Valve (N176) and the Coolant Pump (V50), perform the procedure for determining the malfunction when there is a temperature increase after the evaporator.
• If air flowing out of variable temperature center vent in "Lo " setting for driver's and passenger's side on front A/C control head, Climatronic Control Module (J255)) is cooled in " Cold" setting and not cooled in "Warm" setting, check operation of Left Heat Regulating Valve (N175) and Right Heat Regulating Valve (N176). vehicle diagnosis testing and information system VAS 5051 in the "Guided Fault Finding" function.
• If cooling output on front passenger's side is still adequate but values on driver's side are no longer attained, this is an indication for insufficient refrigerant in refrigerant circuit stratification in evaporator due to lack of refrigerant.
Problems relating to differences between temperature of air emitted by vents with identical setting in air conditioner control mode may be due to the following:
• The cold air doors or warm air doors in the air ducts do not close completely or do not reach their end positions. Refer to => [ Air Intake and Air Guide in Air Conditioner ] Air Intake and Air Guide in Air Conditioner and vehicle diagnosis testing and information system VAS 5051 in the "Guided Fault Finding" function.
• There is air in one or both heat exchangers so there is different flow between them and uneven heat distribution. Refer to=> [ Ventilation System Heat Output and Pump Valve Unit Function ] Ventilation System Heat Output and Pump Valve Unit Function.
• The foam seal may have come loose when installing the heat exchanger allowing air to flow past the heat exchanger.
Under certain operating conditions, residual moisture in refrigerant circuit can lead to an ice build-up at compressor regulator valve. This impedes compressor regulation. Evaporator is excessively cooled and ices up. The freeze-up of the evaporator can be the cause for the following customer complaints:
- After a long drive, A/C system repeatedly or sporadically fails no cooling or heating performance, after switching off vehicle and after a short time, A/C function is OK again.
- After a long drive, windows fog up from inside, windows are also not cleared by then pressing the "Defrost" button, after switching off vehicle and after a short time, A/C function is OK again.
Corrective action:
- Check the measured value for the Evaporator Vent Temperature Sensor (G263) with the "Read measuring value block " function vehicle diagnosis testing and information system VAS 5051 in the "Guided Fault Finding" function.
• If measured value of sensor is too high under operating conditions reported by customer even though A/C system is operating without difficulty at greater than 10 °C, check Evaporator Vent Temperature Sensor (G263) incorrect measured value may cause evaporator to ice up.
• If the sensor measured value is too low under the conditions described by the customer at an ambient temperature greater than 0 °C, less than 0 °C for an extended period of time, there is a malfunction in the refrigerant circuit. Transfer the vehicle to a workshop that has the necessary equipment and trained personnel to perform the work => Refrigerant R134a - Servicing. Notify the workshop about the malfunction.
• Check refrigerant line from evaporator to accumulator (thick tube, low pressure side) with engine running. A heavy layer of ice on this line when the complaint occurs (a thin layer of ice is permitted) indicates that the temperature in the evaporator is too low and the compressor regulation may not be functioning correctly. Transfer the vehicle to a workshop that has the necessary equipment and trained personnel to perform the work => Refrigerant R134a - Servicing. Notify the workshop about the malfunction.
• Notify the workshop about the malfunction. The required work can only be performed there empty the refrigerant circuit, replace the reservoir and then discharge the circuit for at least three hours=> Refrigerant R134a - Servicing.