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) / A/C Control Module (J301) so that temperature of air downstream of evaporator reaches the specified value (approximately 2 to 5 °C):

• Depending on the temperature, engine speed and vehicle voltage supply measured in measuring value block of Climatronic control module / of A/C control module for the activation of A/C compressor regulator valve, a value greater than 75% (0.55 A) is displayed after vehicle start. Refer to Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function. As soon as the temperature measured by the Evaporator vent temperature sensor (G263) nears the target value, the activation, and thus the compressor output, is reduced.

• Under certain operating conditions, moisture in the refrigerant circuit can lead to ice build-up on the A/C compressor regulator valve (and on the 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.

- Vehicles with automatically regulated A/C system: 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) using Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.

- If the sensor measured value 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).

- Is the measured value from the sensor is below the operating condition described by the customer (at an 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.

- 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. If the A/C compressor control is not OK, then inform the workshop of the problem at hand.