Refrigerant Circuit, Discharging
- Work procedure may vary depending on the type of tools selected (the tool-specific operating instructions should therefore be followed). Refer to the A/C Service Station Owner's Manual.
- The refrigerant circuit is to be discharged if parts of the refrigerant circuit are to be removed, if there is any doubt about the quantity of refrigerant in the circuit, when contaminated refrigerant is determined by the gas analysis or if safety precautions so require.
- All of the necessary operating instructions for working with the A/C Service Station for refrigerant can be found in the A/C Service Station Owner's Manual. Refer to the A/C Service Station Owner's Manual.
Discharging:
-- On vehicles with a high-voltage system, switch off (deactivate) the "auxiliary climate control" function. Refer to the Owner's Manual and Infotainment/MMI Operating Manual.
-- Switch off the ignition.
-- Connect the A/C Service Station to the power supply.
Additionally on vehicles with electric operated valves in the refrigerant circuit, which cannot be opened without power:
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.
-- Open the electrically activated valves (not open without current) using the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
All Vehicles
-- Start the A/C Service Station according to the corresponding operating instructions.
-- Remove the closure caps from the refrigerant circuit service connections (refer to the vehicle-specific refrigerant circuit. Refer to Refrigerant Circuit (vehicle-specific Service Information).
-- Connect the A/C Service Station to the refrigerant circuit. Refer to A/C SERVICE STATION ON REFRIGERANT CIRCUIT, CONNECTING .
-- Perform a gas analysis with the A/C Service Station. Refer to REFRIGERANT GAS ANALYSIS, PERFORMING .
If the gas analysis determines that the refrigerant R1234yf is contaminated, extract the refrigerant from the refrigerant circuit (fill in a recycling cylinder) and return it to the gas supplier to be analyzed, processed, or disposed of. Refer to RETURNING CONTAMINATED REFRIGERANT R1234YF FOR ANALYSIS, PROCESSING, OR DISPOSAL .
-- Discharge the refrigerant circuit using the A/C Service Station according to the operating instructions.
Risk of damaging the A/C compressor by the refrigerant circuit vacuum.
- Never start the engine with vacuum in the refrigerant circuit.
There is a possibility of refrigerant oil being extracted from the refrigerant circuit together with the refrigerant. To ensure compressor lubrication, the refrigerant oil in the circuit must be topped up with fresh refrigerant oil. Refer to REFRIGERANT CIRCUIT, CHARGING .
Depending on the version of the A/C Service Station, it can generate a vacuum in the refrigerant circuit when extracting the refrigerant (residual pressure less than approximately 300 mbar (4.35 psi)).
For vehicles with an A/C compressor with no A/C clutch (with an A/C Compressor Regulator Valve -N280-), the engine should not be run for longer than absolutely necessary with the refrigerant circuit empty. Avoid higher engine speeds (A/C compressor always in operation as well).
For vehicles with an A/C compressor with no A/C clutch, the engine may only be started following complete assembly of the refrigerant circuit (avoid high engine speeds).
Depending on the A/C compressor version, there may be a valve installed on the high pressure side of the A/C compressor, which prevents the liquid refrigerant from flowing back into the A/C compressor once the A/C system is turned off. If an A/C compressor with this valve is installed in a vehicle with a refrigerant circuit having an expansion valve, then it may take some time until the pressure in the high pressure side decreases (the expansion valve is cold and the pressure in the low pressure side quickly increases after it is turned off, the expansion valve closes and the refrigerant can flow slowly to the low pressure side). If the A/C compressor is switched on (or the refrigerant circuit is evacuated on the low pressure side), the pressure on the low pressure side goes down, the expansion valve opens and the refrigerant can flow to the low pressure side.
Should work be performed on the vehicle after discharging which does not require using the A/C Service Station.
-- Disconnect the A/C Service Station from the refrigerant circuit and turn it off. Refer to A/C SERVICE STATION, SWITCHING OFF AND DISCONNECTING FROM REFRIGERANT CIRCUIT .
-- Open the refrigerant circuit at a connection location.
Danger of frostbite due to refrigerant coming out under pressure.
Frostbite on the skin and other parts of the body is possible.
- Wear safety gloves.
- Wear protective eyewear.
- Extract refrigerant and open the refrigerant circuit immediately.
- If more than 10 minutes have elapsed since evacuating the refrigerant and the refrigerant circuit was not opened, evacuate the refrigerant again. Evaporation can cause pressure to develop in the refrigerant circuit.
-- Perform the specified procedures on the refrigerant circuit.
Should the refrigerant circuit be evacuated and recharged after the discharging. Refer to REFRIGERANT CIRCUIT, EVACUATING .
After opening the connection locations in the refrigerant circuit seal the open lines and component connections (so that no moisture and dirt can enter these components).
There is a possibility of refrigerant oil being extracted from the refrigerant circuit together with the refrigerant. To ensure compressor lubrication, the refrigerant oil in the circuit must be topped up with fresh oil.
On vehicles fitted with a compressor with A/C Compressor Regulator Valve -N280- the engine should not be run for longer than absolutely necessary with the refrigerant circuit empty (A/C compressor always in operation as well).
On vehicles with an A/C compressor with A/C Compressor Regulator Valve -N280- the engine may only be started when the refrigerant circuit is completely assembled, at the same time avoid high engine speeds.