Refrigerant Circuit, Evacuating: Notes

On vehicles with high-voltage system and additional functions of the A/C system ("heat pump operation" or "cooling the high-voltage battery") valves may be installed in the refrigerant circuit which cannot be opened without power. 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 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 or 100 mbar (1.45 psi)). So that the refrigerant circuit can be completely evacuates (residual pressure less than 5 mbar (72.5 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 pressure at the end of the evacuation process must be smaller than 5 bar (72.5 psi) absolute pressure (the vacuum pump of the A/C service station runs). If during the evacuation process the refrigerant circuit pressure is not smaller than 5 mbar (.07 psi), this may have various causes: For example leaks in the refrigerant circuit or in the connection to the A/C service station causes the evacuation time to be too short the vacuum pump from the A/C service station does not generate the required vacuum or the vacuum sensor from the A/C service station is not correctly calibrated. Refer to the A/C service station Owner's Manual.

An absolute pressure of 5 mbar (0.07 psi) corresponds to for example a absolute pressure of 980 mbar (14.21 psi) 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 Owner's Manual. If after repeating the procedure twice the refrigerant circuit pressure does not stay smaller than 20 mbar (0.29 psi), this may have various causes. If there are leaks in the refrigerant circuit, leaks in the connection from the refrigerant circuit to the A/C service station or in the A/C service station itself, the time for the evacuation time is too short or the time for the vacuum/pressure increase is 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 displayed directly, it can also be the case that only when the vacuum pump is running the current pressure is shown. Refer to the A/C service station Owner's Manual. If the A/C service station only displays the ambient pressure then the display of the refrigerant circuit pressure is dependent on the ambient pressure when turning on (the ambient pressure at 980 mbar (14.21 psi) corresponds to a vacuum of 975 mbar (14.14 psi) 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 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 can also be the case, that the specified absolute pressure in the refrigerant oil raises above the specified 20 mbar (0.29 psi) during the vacuum test. Due to refrigerant (and also due to moisture) which has evaporated from the refrigerant oil on a refrigerant circuit without leaks. If this is the case repeat again and/or adaptation 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 of for evacuate the "Evacuate" function. Refer to the A/C service station Owner's Manual.

Because of the high temperature of the evacuation it can be the case that the refrigerant evaporating from the refrigerant oil can cause the refrigerant circuit pressure to increase during the vacuum test to 20 to 40 mbar (0.29 to 0.58 psi) (absolute pressure). This does not indicate a leak in the refrigerant circuit be 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.