Determining Malfunction if Specified Values Are Not Obtained

Determining Malfunction if Specified Values Are Not Obtained






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. Pressures up to 31 bar may occur due to extremely high performance under severe conditions (such as in southern countries with a hot climate, "stop and go" traffic and high humidity).

• At temperatures below 25° C, the pressure in the refrigerant circuit generally does not rise above 16 bar (the coolant fans run and cool the condensers down).

• Depending on the measured pressure, the A/C control module (J301) A/C Compressor Regulator Valve (N280) and requests the Engine Control Module (ECM) via the CAN-Bus system to actuate the Coolant fan (V7).

• At an absolute pressure of less than approximately 1.2 bar or greater than approximately 32 bar, A/C Control Module (J301) does not switch on the compressor ( A/C Compressor Regulator Valve (N280) is not actuated). The A/C compressor is switched on again only after the measured absolute pressure has become greater than 1.8 bar or less than 16 bar.

• To prevent the A/C compressor from suddenly switching off because there is too much pressure in the in the refrigerant circuit or because the coolant temperature is too high, the A/C control module (J301) controls its power as soon as the refrigerant circuit pressure goes above 30 bar (absolute pressure) or the coolant temperature reaches 115 °C. Full A/C compressor output is released again after the pressure goes below 27 bar. If the coolant temperature goes above 115 °C, the A/C compressor output will continue to be controlled by the A/C control module. At 118 °C it is completely switched off.

• If the refrigerant circuit pressure was greater than 32 bar, the A/C control module switches on the A/C compressor again only when the pressure has decreased below 29 bar.

• Additional information regarding the pressure in the refrigerant circuit can be found in "Guided Fault Finding" using Vehicle diagnosis, testing and information system (VAS5051B) in "Guided Fault Finding" function.