Tech Tip: Mercedes-Benz A/C Off Light Illuminated, A/C Not Functioning
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Tech Tip: Mercedes-Benz A/C Off Light Illuminated, A/C Not Functioning

If you receive customer reports in the above models that the A/C Off light is illuminated and cannot be switched off and the air conditioning is not functional, the Refrigerant Level Temperature Pressure Sensor coding in the AAC unit may need to be set to “INACTIVE.” Follow the below procedure to remedy a specification parameter in the refrigerant level logic circuit.

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If you receive customer reports in the above models that the A/C Off light is illuminated and cannot be switched off and the air conditioning is not functional, the Refrigerant Level Temperature Pressure Sensor coding in the AAC unit may need to be set to “INACTIVE.” Follow the below procedure to remedy a specification parameter in the refrigerant level logic circuit.

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Note: Replacement of the evaporator sensor or the operating unit is not necessary.

Note: Verify that the A/C system is not leaking and is not losing refrigerant.

Models 203, 209, 220 (up to August 2002 production) and 230 (up to August 2003 production)

1. Using STAR Diagnosis, enter the following menus: [Control Units > Air Conditioning > AAC control unit > Actual Values > A/C Control].

2. Observe the value for sensor (B12) Refrigerant Pressure Sensor.

3. Ensure the value for B12 is within specification.

4. Using STAR Diagnosis, enter the following menus: [Control Units > Body > EIS > Control Unit Adaptations > Read Coding and Change if Necessary > Climate Control >Refrigerant Level Check].

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5. Set the coding for Refrigerant Level Check ­“INACTIVE.”

6. Select F3 and transfer coding to the control unit.

7. Remove STAR Diagnosis and verify that the A/C Off light is not illuminated by default and will turn on/off after pressing of the A/C Off switch.

Model 211

1. Using STAR Diagnosis, enter the following menus: [Control Units > Air Conditioning > AAC control unit > Actual Values > A/C Control].

2. Observe the value for sensor B12/2 Refrigerant Level Pressure and Temperature Sensor.

3. Ensure the value for B12/2 is within the Specified Value range.

4. Using STAR Diagnosis, enter the following menus: [AAC > Control Unit Adaptations > Read Codings and Change if Necessary > Workshop ­Coding].

5. Set the coding for Coolant level check via pressure and temperature sensor (“Maximum principle”) to “INACTIVE.”

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6. Select F3 and transfer coding to the control unit.

7. Remove STAR Diagnosis and verify that the A/C Off light is not illuminated by default and will turn on/off after pressing of the A/C Off switch.

Model 215, 220 (as of September 2002) and 230 (as of September 2003)

1. Using STAR Diagnosis, enter the following menus: [Control Units > Air Conditioning > AAC control unit > Actual Values > Temperature Sensor].

2. Observe the value for sensor (B12) Refrigerant Pressure Sensor.

3. Ensure the value for B12 is within specification.

4. Using STAR Diagnosis, enter the following menus: [Control Units > Body > CGW > Control Unit Adaptations > Read Coding and Change if Necessary > Climate Control > Refrigerant Level Check].

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5. Set the coding for Refrigerant Level Check ­“INACTIVE.”

6. Select F3 and transfer coding to the control unit.

7. Remove STAR Diagnosis and verify that the A/C Off light is not illuminated by default and will turn on/off after pressing of the A/C Off switch.

Courtesy of Mercedes-Benz USA, LLC.

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