Malfunction Determination In Case of Deviation From Target Value (Required Cooling Output of A/C System Is Not Achieved)

Malfunction Determination in Case of Deviation from Target Value (Required Cooling Output Of A/C System Is Not Achieved)






Test continuation "A/C compressor activation is switched off"






Continuation of test: "Pressure in refrigerant circuit increases"






• The pressure in the refrigerant circuit depends on several factors. However, in general, the pressure should not exceed 20 bar at an ambient temperature of 20 to 25° C (68 to 77 °F). Under extreme conditions (for example, stop and go traffic at a high ambient temperature and high relative humidity), pressures up to 31 bar may occur due to the extremely high cooling output.

• At ambient temperatures below 25° C (77 °F), pressure in refrigerant circuit does not normally exceed 16 bar (coolant fans run and cool condenser).

• The Climatronic control module (J255) , calculates the pressure in the refrigerant circuit via the measured value of the A/C pressure/temperature sensor (G395) and displays it using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

• At an absolute pressure of less than approximately 1.8 bar or greater than approximately 32 bar, the Climatronic control module does not switch on the A/C compressor (the A/C compressor regulator valve (N280) is not activated). The A/C compressor is only switched on once the absolute pressure becomes greater than 1.8 bar or less than 16 bar.

• For additional information regarding pressure in the refrigerant circuit, refer to the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

• To prevent abrupt A/C compressor shutoff due to excessive pressure in refrigerant circuit or an excessive coolant temperature, the Climatronic control module regulates the A/C compressor output. As soon as pressure in refrigerant circuit exceeds 30 bar (absolute pressure), full A/C compressor performance is only enabled again after pressure has become less than 27 bar, or coolant temperature exceeds 115° C (239 °F) (it is switched off completely at 118° C (244 °F)).