Ice Formation on Evaporator, Localizing Malfunction

Ice Formation on Evaporator, Localizing Malfunction

• The A/C compressor regulator valve (N280) is activated by the Climatronic control module (J255) , via the vehicle electrical system control module (J519) so that the temperature of the air downstream from the evaporator reaches the specified value (approximately 2-5° C (35-41°F)):

• After vehicle start, a value greater than 0.55 A is displayed in the relevant measured value of the Climatronic control module depending on the measured temperature, the engine speed, and the vehicle voltage using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function. As soon as the temperature measured by evaporator vent temperature sensor (G263) nears the specified 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/or 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, the A/C system repeatedly or sporadically fails (no cooling or heating performance), after switching off the vehicle and after a short time, A/C function is OK again.

- After a long drive, the windshield, rear window and/or door windows fog up on the inside. Pressing the Defrost button of the Climatronic control module, does not clear the windshield, rear window, and/or door windows. After turning off the vehicle and waiting a short period, the function of the A/C system is OK again.

Checking

- In the "Read measured values" function, check the measured value of the evaporator vent temperature sensor (G263) using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

- If the measured value of the evaporator vent temperature sensor is too high under the operating conditions described by the customer (although the A/C system is working properly, depending on the ambient temperature, greater than 10° C (50 °F), for example), check the evaporator vent temperature sensor, and compare the measured values of the evaporator vent temperature sensor to the measured values of the vent temperature sensors (G150) / (G151) (an incorrect measured value can cause the evaporator to ice up) using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

- Is the measured value from the evaporator vent temperature sensor evaporator vent temperature sensor is below the adjustment requirement described by the customer (at a temperature above 0° C, longer when it is lower than 0° C (32 °F)). 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 the refrigerant line on the low pressure side (larger diameter line between the inner heat exchanger connection and the A/C compressor) with the engine running. Refer to=> [ Refrigerant Circuit Components Overview ] Refrigerant Circuit Components Overview. 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.

Check the evaporator in the case of suspicion of icing

- Open the vent in the instrument panel and the rear center console.

- In the case of a Comfort A/C system, open the vents in the B-pillar.

- Start the engine.

- Switch the A/C compressor on by selecting the "Auto" mode on the Climatronic control module (J255) (the indicator lamps in the AUTO buttons and the AC button illuminate).

- Via the rotary switches of the Climatronic control module, the temperature preselection is set to cold (for the driver and front passenger side).

- On the Climatronic control module set the lowest possible speed for the fresh air blower (V2) (lowest possible cooling output of the A/C unit).

- On the rear A/C display control head (E265) set the temperature preselection to cold (if present, for the left and right sides).

- Set the rear temperature selection potentiometer (G538) to cold.

- Set the air flow direction via the rotary switches on the Rear A/C display control head to the vents in the rear center console.

- On the rear A/C display control head set a medium speed for the fresh air blower.

- Set the engine speed to 2000 RPM.

- In the "Read measured values" function, read out the measured value of the evaporator vent temperature sensor (G263) using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

- If the measured value of the evaporator vent temperature sensor (G263) is too low (at ambient temperature above 0° C, colder than 0° C for a long period of time). 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.

In the case of icing at the expansion valve

- After a long drive, the A/C system repeatedly or sporadically fails (no cooling or heating performance), after switching off the vehicle and after a short time, A/C function is OK again.

- Bring the vehicle to a workshop that has the necessary tools and where the work can be performed by qualified personnel.

- Bring the problems determined to the attention of the workshop.