Determining Malfunction if Specified Values Are Not Obtained

Determining Malfunction if Specified Values Are Not Obtained

The required values are not reached during the cooling performance test => [ Cooling Output, Checking ] Cooling Output, Checking.

- Select "read measured values block" vehicle diagnosis testing and information system VAS 5051 in the "Guided Fault Finding" function.

- Repeat cooling performance test. Refer to => [ Cooling Output, Checking ] Cooling Output, Checking.





The pressure in the refrigerant circuit increases.

- Open hood.

- Repeat cooling performance test. Refer to=> [ Cooling Output, Checking ] Cooling Output, Checking.





• Pressure in refrigerant circuit is governed by various factors of influence. However, at an ambient temperature between 20 to 25 °C the pressure should not exceed more than 20 bar. Due to high coolant performance, pressures up to 31 bar may occur under extreme operating conditions like. in southern countries with high ambient temperatures, "stop and go" traffic and high humidity).

• At ambient temperatures below 25 °C, pressure in refrigerant circuit does not normally exceed 16 bar radiator fan runs and cools condenser.

• The Climatronic Control Module (J255) front A/C control head calculates the pressure in the refrigerant circuit via the duty cycle signal from the High Pressure Sensor (G65)). At a duty cycle less than 12.5% (corresponds to approximately 1.8 bar absolute pressure) and greater than 87.5% (corresponds to approximately 32 bar absolute pressure), front A/C control head does not switch on compressor (A/C Compressor Regulator Valve (N280) is not activated). Compressor is only switched on again after duty cycle has become greater than 12.5% (corresponds to 1.8 bar absolute pressure) or less than 48% (corresponds to 16 bar absolute pressure).

• To prevent abrupt compressor shut-off in case of excessive pressure in refrigerant circuit or excessive coolant temperature, front A/C Control Head regulates compressor performance:

- When the pressure in the refrigerant circuit exceeds 30 bar (absolute pressure). Full compressor performance is only possible again once the pressure drops below 27 bar.

- As soon as the coolant temperature exceeds 115° C full shutdown at 118° C.

- If pressure in refrigerant circuit was greater than 32 bar duty cycle greater than 87.5%, compressor is only switched on again by front A/C control head if pressure drops below 29 bar duty cycle less than 84%.

• Additional information regarding the pressure in the refrigerant circuit can be found in Guided Fault Finding "Read measured value block" vehicle diagnosis testing and information system VAS 5051 in the "Guided Fault Finding" function.