A/C system cooling performance, testing: Notes

NOTE: Under certain operating conditions, residual moisture in refrigerant circuit can lead to an ice build-up at compressor regulator valve. 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 pressing the "Defrost" button, after switching off vehicle and after a short time, A/C function is OK again.
Corrective action:
For vehicles as of model year 2002 and a compressor with A/C Compressor Regulator Valve -N280-, check measured value of Evaporator Vent Temperature Sensor -G263-. See DISPLAY GROUP 010: MEASURING VALUES FOR EVAPORATOR VENT TEMPERATURE SENSOR -G263-, FRESH AIR INTAKE DUCT TEMPERATURE SENSOR -G89-, OUTSIDE AIR TEMPERATURE SENSOR -G17- AND CALCULATED OUTSIDE TEMPERATURE TRANSMITTED TO INSTRUMENT CLUSTER . If measured value of the sensor is too low under operating conditions specified by customer (at an ambient temperature above 0 6 C, colder than 0 C for a long period of time although A/C Compressor Regulator Valve -N280- is not currently being activated), transfer vehicle to an authorized service shop for A/C systems.
In vehicles without Evaporator Vent Temperature Sensor -G263- e.g. via Sender for outlet temperature, floor outlet -G192-, check at the adjustment: "Temperature Lo" for driver's- and passenger side, 4 or 5 bars for fresh air blower RPM, air outlet in footwell and fresh air operation under operating conditions specified by customer. If measured value of the sensor is too low (at an ambient temperature above 0 ° C, colder than 0 ° 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 indicates that the temperature in evaporator is too low, transfer 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 accumulator and then evacuating the refrigerant circuit for a minimum of 3 hours).