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.
Searching For Refrigerant Circuit Leaks With Compressed Air Or Nitrogen
A 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.
Use the service connection for the compressed air or nitrogen.
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.
- The maximum permitted working pressure is 15 bar.
- When testing for leaks with nitrogen, always work with a pressure reducer for nitrogen bottles.
-- Find the location of the leak by listening for the sound of venting gas. An Ultrasonic tester -V.A.G 1842- will aid in detecting the origin of noise.
-- Use clean, dry compressed air to force the nitrogen out of the refrigerant circuit. The nitrogen must not get into the Service bottle. Reason: gases that do not condense do not get into the Service bottle.
-- 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, FINDING LEAKS WITH ELECTRONIC LEAK DETECTOR VAG 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 REFRIGERANT CIRCUIT, FINDING LEAKS WITH LEAK DETECTION SYSTEM VAS 6201 OR VAS 6196 .
-- Empty the refrigerant circuit, if necessary. Refer to REFRIGERANT CIRCUIT, DISCHARGING WITH SERVICE STATION .
-- Evacuate and check the vacuum display again over several hours. Only when the vacuum is maintained can the refrigerant circuit be charged.
NO RELATED
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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.