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.
Pressure Relief Valve
The pressure relief valve is installed on the A/C compressor or receiver/dryer.
At a pressure of approximately 38 bar (551.14 psi) positive pressure, the valve opens and closes again once pressure has dissipated (at approximately 35 bar (507.63 psi)).
Refrigerant does not escape completely.
Depending on the version, a transparent plastic washer -B- may be installed on the pressure relief valve -A-, which breaks off as soon as the valve is activated.
Depending on the pressure relief valve version -A-, an additional cover -C- can be slid onto the pressure relief valve -A-. If the pressure in the refrigerant circuit does rise above the pressure relief valve -A- opening pressure and the pressure relief valve opens, the refrigerant does not escape in one direction, but rather it is distributed through the openings -D- under the cover -C-.
If it is necessary to replace a pressure relief valve -A- pay attention to the tightening specification when installing (depending on the manufacturer of the A/C compressor and the version). On "Denso", "Sanden" and "Valeo" A/C compressors an O-ring is installed (tightening specification currently 10 Nm on "Denso" and "Zexel- / Valeo" as well as 15 Nm on "Sanden" A/C compressor). On a "Delphi" A/C compressor, for example, a seal is installed (tightening specification is currently 15 Nm).
Replace the seals (seal or O-ring). Refer to the Parts Information.
If the seals (seal or O-ring) that are installed on the pressure relief valve are not available as a replacement part, the removed seals may be used as an exception (check for damage before installing). If the removed seal is damaged or deformed if necessary replace with a commercially available component. Refer to the Parts Information.
After charging the refrigerant circuit, check the installed pressure relief valve for leaks using an electronic leak detector, for example.
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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.