Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Evacuating Refrigerant Circuit
- The work procedure is always to be performed as described in the operating instructions for the A/C service station.
- Quantity of refrigerant oil in circuit checked and if necessary corrected. Refer to REFRIGERANT OIL CAPACITIES .
- Check quantity of refrigerant in the service station.
The refrigerant circuit must be evacuated before it is filled with refrigerant (vacuum). Moisture is also extracted from the circuit.
Leaks may be found when evacuating the refrigerant circuit.
Evacuating
- Do not start the engine during the evacuation process or when there is a vacuum in the refrigerant circuit.
- The A/C compressor could be damaged if the engine is started when there is a vacuum in the refrigerant circuit.
- Only start the engine when the refrigerant circuit is filled.
-- Switch off the ignition.
-- Connect service station to power supply.
-- Connect charging hose of service station to vehicles refrigerant circuit with quick-release coupling adapter (refer to vehicle-specific refrigerant circuit). Refer to General Information (vehicle-specific repair information).
-- Only tighten the handwheel on the quick-release coupling adapter just enough so the valves in the service connections are securely open. Do not put too much pressure on the valve.
If pressure is to be measured after charging system on vehicles with a service connection on one side of the refrigerant circuit only, use valve adapter and charging hose with valve opener. Refer to CONNECTING FOR MEASURING AND TESTING, ONE SERVICE CONNECTION .
-- Switch on service station and evacuate refrigerant circuit for at least 30 minutes. The pressure reading must indicate an absolute pressure of less than 10 mbar (corresponding to 990 mbar vacuum).
At this pressure, both green LEDs light for example on service station V.A.G 1885 .
-- Switch off service station and allow to stand for at least 1 hour.
- If the vacuum display (LED chain) does not change, the system is free of leaks and can be charged.
- A current vacuum reading (LED) is only obtained using V.A.G 1885, for example after pressing the "Evacuate" button again.
- If with this service station the upper (green) LEDs do not light immediately after switching on, either the refrigerant circuit is leaking or there is still residual moisture/refrigerant in the circuit.
If the vacuum is not maintained or cannot generate a sufficient vacuum, perform the following:
- Did the pressure in refrigerant circuit increase slowly after evacuating, for example, through evaporation.
-- If it is possible that the refrigerant circuit may have leaks, evacuate and check the vacuum display again over several hours Only when the vacuum is maintained can the refrigerant circuit be charged.
-- If the refrigerant circuit is sealed, it can be filled.
- If there is a leak that allowed enough air to enter during evacuation that the A/C service station cannot generate a sufficient vacuum or that the vacuum is lost immediately after switching the A/C service station off:
-- Determine the location of the leak in the refrigerant circuit as follows:
- A large leak can be identified if a maximum of pressure of 15 bar can be generated in the refrigerant circuit using clean, dry compressed air or nitrogen. Refer to REFRIGERANT CIRCUIT FLUSHING WITH COMPRESSED AIR AND NITROGEN . If the leak is large enough, the sound of escaping air or gas can be heard at the location of the leak.
- Add the compressed air or nitrogen to the closed refrigerant circuit through the service connection after fitting it with a quick-release connector adapter.
- The quick-release coupling adapter for service connections can be connected to the air compressor using a modified filler hose -A- (for example, with 5/8" 18 UNF threads, different from the threads on the quick-release coupling adapter) and a suitable adapter -B-. Refer to IMPROVISED TOOLS . This keeps humidity, oil and dirt coming out of the workshop compressed air system from getting into the A/C refrigerant circuit. Also use a combination fine-gauge filter for compressed air systems such as those that are standard in paint shops. Install it between the compressed air system and the filler hose -A-.
- A compressed gas cylinder filled with nitrogen -3- can be connected to the closed refrigerant circuit using a pressure gauge battery with a pressure reducer for nitrogen (maximum reduction pressure: 15 bar) -1- and a filler hose -2- (for example, with 5/8" 18 UNF threads) connected to the service connection. A quick-release coupling adapter must also be connected to the service connection. Refer to IMPROVISED TOOLS .
-- Slowly increase the pressure in the refrigerant circuit to a maximum of 15 bar.
- Nitrogen can leak uncontrolled from the cylinder.
- Make exclusive use of pressure reducers for nitrogen cylinders (maximum work pressure 15 bar).
- When testing for leaks with nitrogen (maximum permissible pressure 15 bar), always work with a pressure reducer for nitrogen bottles.
- Use appropriate extraction units to draw off gas mixture escaping from components.
-- Find the location of the leak by listening for the sound of venting gas.
-- Repair the leak.
-- Evacuate and again observe the vacuum display over a period of hours. Only when the vacuum is maintained can the refrigerant circuit be charged.
- If there is a leak that is small enough that no air or very little air vents through it and the A/C service station can generate a sufficient vacuum: The vacuum indicator does not increase after switching the A/C system service station or only increases slowly, indicating that air is only entering through a small leak.
-- Add 100 grams of refrigerant to the circuit, find the location of the leak using an electronic leak detector and repair it. Refer to REFRIGERANT CIRCUIT, TRACING LEAKS USING ELECTRONIC LEAK DETECTOR V.A.G 1796 . Or add UV contrast dye to the refrigerant and find the location of the leak with the leak detection system VAS 6201 and repair it. Refer to LEAK DETECTION ON REFRIGERANT CIRCUIT USING LEAK DETECTION SYSTEM VAS 6201 .
-- Empty the refrigerant circuit, if necessary. Refer to DRAINING REFRIGERANT CIRCUIT .
-- Evacuate and check the vacuum display again over several hours. Only when the vacuum is maintained can the refrigerant circuit be charged.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.