Ice Formation on Evaporator, Localizing Malfunction

Ice Formation on Evaporator, Localizing Malfunction

• A/C Compressor Regulator Valve (N280) is activated by Climatronic control module (J255) so that temperature of air downstream of evaporator reaches the specified value (approximately 2 to 5° C):

• A value greater than 75% (0.55 A) will be displayed in the measured values block for the A/C compressor regulator valve Climatronic control module after starting the vehicle, depending on the measured temperature, engine RPM and the electrical system voltage. As soon as temperature measured by the evaporator vent temperature sensor (G263) approximates the specified value, the activation is rescinded and thus the compressor output is reduced. Refer to (VAS5051B) under "Guided Fault Finding."

• Under certain operating conditions, residual moisture in refrigerant circuit can lead to an ice build-up at A/C Compressor Regulator Valve (N280) (and at expansion valve). A/C compressor control is reduced by this ice build-up, evaporator is cooled too intensely and freezes. 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 from the evaporator vent temperature sensor (G263) with the "Read measuring value block" function using (VAS5051B) under "Guided Fault Finding."

- If the sensor measured is too high under the operating conditions reported by the customer (even though the A/C system is operating without difficulty at greater than e.g. 10° C, depending on ambient temperature), check the evaporator vent temperature sensor (an incorrect measured value may cause evaporator the ice up).

- When the measured value from the sensor is below the operating condition described by the customer (at a temperature above 0° C, longer when it is lower than 0° C). Bring vehicle to a workshop that has the necessary tools and in which the work can be performed accordingly by qualified personnel. Bring the problems determined to the attention of the workshop.

- Check refrigerant line from evaporator (from expansion valve) to A/C compressor (thick tube, low pressure side) with engine running. If this line is thickly iced-up when a problem occurs (a very thin layer of ice is permitted), this indicates that the temperature in the evaporator is too low. Bring vehicle to a workshop that has the necessary tools and in which the work can be performed accordingly by qualified personnel. (it is possible that A/C compressor regulation is not OK). Bring the problems determined to the attention of the workshop.