Refrigerant Circuit, Evacuating: Notes

For vehicles with a high-voltage system and additional A/C system functions (heat pump operation" or "cooling the high-voltage battery") valves may be installed in the refrigerant circuit that cannot be opened without current. These valves are opened and closed for example via a step motor and after switching off the ignition are no longer activated. To completely discharge, correctly evacuate and charge the refrigerant circuit, no sections may be closed. Therefore these valves must be opened before performing this work. Refer to Refrigerant Circuit (vehicle-specific service information) and Use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

The check valves in the refrigerant circuit in the flow direction have a specified residual pressure (approximately 0.1 bar (1.45 psi) or 100 mbar (1.45 psi)). So that the refrigerant circuit can be completely evacuated (residual pressure less than 5 mbar (0.07 psi)) all electrically activated valves must be opened.

Dirt or a rough surface on the service connections due to corrosion can cause seal damage, which can then cause premature failure of the quick-release couplings.

The vacuum at the end of the evacuation process must be less than 5 mbar (0.07 psi) absolute pressure (running vacuum pump of the A/C Service Station). If during the evacuation process the refrigerant circuit pressure is not smaller than 5 mbar (0.07 psi), this may have various causes: For example, a leak in the refrigerant circuit or in the connection to the A/C Service Station, the time set for the evacuation process is too short, the vacuum pump for the A/C Service Station does not generate the required amount of vacuum, or the vacuum sensor on the A/C service station is not calibrated correctly. Refer to the A/C Service Station Owner's Manual.

With an ambient pressure of 980 mbar (14.21 psi), for example, an absolute pressure of 5 mbar (0.07 psi) equates to a vacuum of 975 mbar (14.14 psi).

At the end of the vacuum/pressure increase test the refrigerant circuit pressure must not be higher than 20 mbar (0.29 psi) absolute pressure. If the refrigerant circuit pressure during the vacuum/pressure increase test is greater than 20 mbar (0.29 psi), the vacuum pump is switched on and the procedure begins again. Refer to the A/C Service Station Operating Instructions. If the procedure is repeated for a second time and the refrigerant circuit pressure still does not stay under 20 mbar (0.29 psi), this may have various causes. For example, a leak in the refrigerant circuit, a leak in the connection from the refrigerant circuit to the A/C Service Station or in the A/C Service Station itself can make the time for the evacuation process too short and the time for the vacuum/pressure increase test too long.

If it is suspected that a leak in the refrigerant circuit is present if necessary switch off the A/C Service Station and let it sit as long as possible (for example one hour to check for leaks in the refrigerant circuit). Refer to the A/C Service Station Owner's Manual.

Depending on the version of the A/C Service Station, the refrigerant circuit pressure is immediately displayed; however, it is also possible that only when the vacuum pump is running is the current pressure shown. Refer to the A/C Service Station Owner's Manual. If the A/C Service Station only displays the ambient pressure, then the refrigerant circuit pressure display depends on the ambient pressure when activated (if the ambient pressure is 980 mbar (14.21 psi), a vacuum of 975 mbar (14.14 psi) equates to a residual pressure of 5 mbar (0.07 psi) absolute pressure).

If the refrigerant circuit was opened, a small amount of moisture may have entered the refrigerant circuit. If this is the case, evacuate the refrigerant circuit for at least 30 minutes (refrigerant circuit pressure less than 20 mbar (0.29 psi) before filling).

If refrigerant was extracted (to check the capacity) and the refrigerant circuit is only evacuated to fill it again (the refrigerant circuit was not opened and has no leaks) it is enough to evacuate the refrigerant circuit for five minutes and no time or only a short amount of time (for example one minute) is needed adjust the vacuum/pressure increase test (no air and no moisture has entered the refrigerant circuit).

Depending on the quantity of refrigerant oil in the refrigerant circuit, the age and the mileage of the vehicle, the design of the refrigerant circuit etc., it is also possible that, on a leak-free refrigerant circuit, the specified absolute pressure in the refrigerant circuit rises over the specified 20 mbar (0.29 psi) during the vacuum test because of the refrigerant (and possibly even moisture) that has evaporated from the refrigerant oil. If this is the case, repeat the procedure again if necessary and/or adjust the pre-set times accordingly.

Depending on the version of the A/C Service Station the current refrigerant circuit pressure is constant or is displayed after switching off for example the "Evacuate" function. Refer to the A/C Service Station Owner's Manual.

Due to the high evacuation temperature, it may be that the refrigerant evaporating from the refrigerant oil is increasing the refrigerant circuit pressure to 20 to 40 mbar (0.29 to 0.58 psi) (absolute pressure) during the vacuum test. This does not indicate a leak in the refrigerant circuit but depending on the version of the A/C Service Station can lead to a displayed malfunction. If necessary evacuate the refrigerant circuit again and monitor the vacuum indicator over a longer time, once the vacuum is maintained and it is ensured that there are no leaks in the refrigerant circuit, the system may be filled.