Determining Malfunctions If Specified Values Are Not Obtained

Determining Malfunctions if Specified Values Are Not Obtained

- In Climatronic control module (J255) Guided Fault Finding, select in "read measured values block" the display group for the refrigerant circuit pressure and activation of the A/C compressor regulator valve (N280) using Vehicle Diagnosis, Testing and Information System VAS 5051 in "Guided Fault Finding".

- Repeat cooling performance test, refer to=> [ Test Requirements ] Test Requirements.






Continuation of test "Pressure in refrigerant circuit increases"

- Open hood.

- Repeat cooling performance test, refer to => [ Test Requirements ] Test Requirements.






• Pressure in refrigerant circuit is governed by various factors of influence. However, at an ambient temperature between 20 to 25 °C (68 to 77 °F) the pressure should not exceed more than 20 bar (290 psi). Due to high coolant performance, pressures up to 31 bar may occur under extreme operating conditions (for example, in southern countries with high ambient temperatures, stop and go traffic and high humidity).

• The pressure in the refrigerant system does not increase above 16 bar at ambient temperatures lower than 25 °C (77 °F) (the Coolant Fan runs and cools the condenser).

• The Climatronic control module (J255) 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 approximately 1.8 bar absolute pressure (26 psi)) and greater than 87.5% (corresponds approximately 32 bar (464) absolute pressure), Climatronic Control Module does not switch on the 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 (26 psi)) or less than 48% (corresponds to 16 bar absolute pressure (232 psi)). Check using Vehicle Diagnosis, Testing and Information System VAS5051 in the "Guided Fault Finding" function.

• If the pressure in the refrigerant circuit or the engine coolant temperature is too high, Climatronic control module regulates the compressor performance (to avoid sudden compressor cut-off). As soon as pressure in refrigerant circuit exceeds 30 bar (absolute pressure)(435 psi), full compressor performance is only enabled again after pressure has become less than 27 bar (391), or coolant temperature exceeds 115° C (239 °F) (it is switched off completely at 118° C (244 °F)).

• If the pressure in the refrigerant circuit was greater than 32 bar (464 psi) (duty cycle greater than 87.5%) the compressor is switched on again by Climatronic control module, if pressure drops below 29 bar (420 psi) (duty cycle is less than 84%).

• Additional information regarding pressure in the coolant circuit, refer to Vehicle Diagnosis, Testing and Information System VAS5051 in the "Guided Fault Finding" function.