Checking
Checking
- Measure ambient temperature (must be greater than 15 degrees C).
- Close doors, hood, windows and sunroof.
- Open all dash panel vents.
- Switch ignition on.
- Set "Econ" mode on MMI.
- Close vents in "B" pillar.
- Set handwheel for variable temperature center vent to "Warm".
- Start engine.
- Initiate On Board Diagnostic (OBD) of A/C system Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
- Select the "Read measuring value block" function display group "001" in Climatronic Control Module J255. Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
- Check display in display zones:
- Display field "2" shows 0% (compressor is switched off)
- Display field "4" shows that the pressure in the refrigerant circuit measured at ambient temperature is the same or greater as the table value.
Ambient temperature in degrees C Pressure display (in bar absolute)
15 4,7
20 5,6
25 6,6
30 7,6
35 8,8
NOTE:
- In terms of absolute pressure, 0 bar corresponds to an absolute vacuum. Normal ambient pressure equals approx. 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 (e.g. radiator), pressure displayed with warm engine will be slightly higher than that given for the respective ambient temperature.
- If pressure displayed is below that indicated in table:
- Check signal of High Pressure Sensor G65. Testing and Inspection
- If no malfunction can be detected at High Pressure Sensor G65, there is insufficient refrigerant in circuit, deliver vehicle to an A/C system service point workshop (insufficient refrigerant in circuit).
If pressure in refrigerant circuit is OK:
- Switch on compressor, select "Auto" mode on Climatronic Control Module J255 or on MMI (Multi Media Interface) to do so.
- Select temperature preselect for drivers and front passengers side to "Lo" on Climatronic Control Module J255.
- Set direction of air flow to "instrument panel vents" on Climatronic Control Module J255.
- Select display group "001" in function "Read Measuring Value Block". Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
- Check display in display zones:
- Display field "2" shows a duty cycle greater than 30% (A/C Compressor Regulator Valve N280 is activated, compressor is switched on)
- Display field "1" shows a current greater than 0.3 A (current flows via A/C Compressor Regulator Valve N280, compressor is switched on)
- The displayed pressure in display field "4" rises above the value with the compressor switched off.
NOTE:
- A/C Compressor Regulator Valve N280 is activated by Climatronic Control Module J255 such that temperature of air downstream of evaporator reaches specified value (approx. 2 to 5 degrees 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 approximates the specified value, activation is reduced 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 (e.g. 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.
- 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 measured value of Evaporator Vent Temperature Sensor G263, (function "Read measuring value block" display group "018"). Vehicle Diagnosis, Testing and Information System VAS 5051 in "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 e.g. 10 degrees C), check Evaporator Vent Temperature Sensor G263 (incorrect measured value may cause evaporator to ice up).
- If measured value of the sensor is too low under operating conditions reported by customer (at an ambient temperature above 0 degree C, colder than 0 degree C for a long period of time), transfer vehicle to an authorized service shop for A/C systems.
- Check refrigerant line from evaporator to accumulator (thick tube, low pressure side) with engine running. If this line is thickly iced up when complaint occurs (a very thin layer of ice is permitted), this also indicates that temperature in evaporator is too low, take vehicle to an authorized service shop for A/C systems.
- Bring the determined deficiency to the attention of the authorized service shop for A/C systems, the necessary work can only be performed there (draining refrigerant circuit, replacing reservoir and then evacuating refrigerant circuit for minimum of 3 hours).
- If no or very little current is displayed in display field "1", check actuation of A/C Compressor Regulator Valve N280. A/C System Heat Output and Pump Valve Unit, Checking
- If pressure displayed in display group "4" does not change and compressor actuation is OK (display field "1" and "2"), there is a malfunction in refrigerant circuit, take vehicle to A/C system service point workshop.
- Press button for recirculating-air mode on Climatronic Control Module J255 (symbol for "recirculating-air mode" lights up in button).
- Set engine speed of 2000 rpm (start of time measurement).
- Select display group "018" in "Read measuring value block" function Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
- Compare displayed measuring value (of Evaporator Vent Temperature Sensor G263) in display field "1" with values in 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.
NOTE:
- If the requested values are not obtained, check measured value of Evaporator Vent Temperature Sensor G263, compare measured values displayed in display group "018", display fields "1" and "017" with display fields "1" and "2":
- If measured value in both display fields "1" or "2" of display group "017" deviates only slightly from measured value of display group "018": Perform "Identifying malfunctions if specified values are not obtained". Measures to Be Taken If Readout Does Not Match Specification
- If measured value of Evaporator Vent Temperature Sensor G263 is greater than measured value of Left Vent Temperature Sensor G150 and Right Vent Temperature Sensor G151, check Evaporator Vent Temperature Sensor G263 for proper installation and perform electrical test for this sensor, Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
- The function of the air conditioning is recognizable, e.g. 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 displayed measured value (of Evaporator Vent Temperature Sensor G263) in display field "1" of display group "018" with measured values of display group "017" display field "1" and "2" (Left Vent Temperature Sensor G150 and Right Vent Temperature Sensor G151).
- After 5 minutes, measured values in display group "017" display field "1" and "2" (Left Vent Temperature Sensor G150 and Right Vent Temperature Sensor G151) must not be more than 3 degrees C higher than value in display field "1" of display group "018" (of Evaporator Vent Temperature Sensor G263).
NOTE:
- If required values are not obtained, compare displayed measuring values in display group "017" display fields "1" and "2" with each other:
- If measured value in one of the two display fields "1" or "2" is OK, check activation and function of Left Heat Regulating Valve N175, Right Heat Regulating Valve N176 and Coolant Pump V50. A/C System Heat Output and Pump Valve Unit, Checking Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
- If no fault is found at Left Vent Temperature Sensor G150 and Right Vent Temperature Sensor G151 as well as at Left Heat Regulating Valve N175, Right Heat Regulating Valve N176 and Coolant Pump V50, perform "Identifying malfunctions at temperature increase downstream of evaporator".
- - If no fault is found at Left Vent Temperature Sensor G150 and Right Vent Temperature Sensor G151 as well as at Left Heat Regulating Valve N175, Right Heat Regulating Valve N176 and Coolant Pump V50, perform "Identifying malfunctions at temperature increase downstream of evaporator".
- Temperature of air flowing out of "center" instrument panel vents can also be measured e.g. using a standard thermometer.
- If air flowing out of variable temperature center vent in "Lo" setting for drivers and passengers side on, 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 "Guided Fault Finding" function.
- If cooling output on front passengers side is still adequate but values on drivers 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:
- Cold-air flaps or warm-air flaps in air ducts do not close completely or do not reach their end positions and Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding" function.
- There is air in one or both heater cores (effecting different flow through heater cores and uneven heat distribution). A/C System Heat Output and Pump Valve Unit, Checking
- A foam seal has loosened during installation of heater cores and air may flow past heater core.