Determining Malfunctions On A/C System

Determining Malfunctions On A/C System

• The connector to A/C Compressor Regulator Valve (N280) and the connector to the electric engine mounts are identical in construction. If, for example, these connectors are interchanged (this is possible for certain engines), no entry appears 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 A/C 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). The A/C function is OK again after switching the vehicle off for a short time.

• After a long drive, windows fog up from inside, windows are also not cleared by then pressing the Defrost button, after turning off the vehicle (or turning off the A/C system) and after a short time, A/C function is OK again.

Corrective action:

- Check measured value of Evaporator Vent Temperature Sensor (G263) (via Guided Fault Finding of the Climatronic Control Module (J255) ) in the "Read measuring value block" function using, Vehicle Diagnosis, Testing and Information System VAS5051 in the "Guided Fault Finding".

• 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 for example, 10 °C (50 °F)), check Evaporator Vent Temperature Sensor (an incorrect measured value may cause evaporator to ice-up).

• If the measured value of the Evaporator Vent Temperature Sensor under the conditions of use specified by the customer is too low (at an ambient temperature above 0 °C (32 °F), colder than 0 °C (32 °F) for an extended period of time), check the A/C Compressor Regulator Valve, refer to => [ A/C Compressor Regulator Valve, Checking Activation Signal ] A/C Compressor Regulator Valve (N280), Checking Activation Signal. If the fault cannot be found, bring vehicle to a workshop that has the necessary tools and in which the work can be performed accordingly by qualified personnel.

• Check refrigerant line from evaporator to compressor (thick tube, low pressure side) with engine running. When a complaint occurs, if this line is severely iced-up (a thin layer of ice is permitted), this also shows that the temperature in the evaporator is too low, check activation of A/C Compressor Regulator Valve, refer to => [ A/C Compressor Regulator Valve, Checking Activation Signal ] A/C Compressor Regulator Valve (N280), Checking Activation Signal, if no malfunction can be detected, bring the vehicle to a workshop that has the necessary tools and where the work can be performed by qualified personnel.

• Notify the workshop about the malfunction. The required work can only be performed there (check the pressure in the refrigerant circuit, drain the refrigerant circuit, replace the dryer cartridge and then evacuate the refrigerant circuit for at least 3 hours).

• In "Guided Fault Finding" under "read measured values block" read the measured value from A/C Compressor Regulator Valve. If no current or an extremely low current is displayed in measured values block, check activation of A/C Compressor Regulator Valve, refer to => [ A/C Compressor Regulator Valve, Checking Activation Signal ] A/C Compressor Regulator Valve (N280), Checking Activation Signal and Vehicle Diagnosis, Testing and Information System VAS5051 in the "Guided Fault Finding" function.

• Ice build up can occur on the evaporator under extreme circumstances for particularly unfavorable A/C system settings (for example, airflow direction is set to the instrument panel vents and these vents are closed, set to MAX AC for a minimal fresh air blower speed). With this setting, there is no air flowing through the evaporator making the temperature at the evaporator vent temperature sensor (G263) higher than the actual evaporator temperature. It can be assumed for the A/C system regulator, that the measured value of the evaporator vent temperature sensor has the actual evaporator temperature and continues to activate the A/C compressor regulator valve and the evaporator cools too much.