my BMW 3 Series E90/E91 AC suddenly stopped working, why?

Solution

1. Preparation

• Gather tools: OBD-II scanner, multimeter, manifold gauge set, basic hand tools, and safety gloves.
• Ensure the vehicle is parked on a level surface and the engine is off.

2. Inspect and Replace Fuse

• Locate the fuse box (usually under the dashboard or in the engine compartment).
• Remove the cover and locate the AC fuse.
• Use a multimeter to check for continuity; if faulty, replace with a new fuse of the same amperage.

3. Testing the AC Compressor

• Start the engine and turn on the AC to the maximum setting.
• Use the multimeter to check for voltage at the AC compressor connector.
• If no voltage is detected, trace the wiring back to the relay and check for faults.

4. Refrigerant Pressure Check

• Connect the manifold gauge set to the low-pressure and high-pressure service ports.
• Start the engine and turn on the AC; note the pressure readings.
• If pressure is low, it may indicate a refrigerant leak; proceed to recharge the system after fixing any leaks.

5. Inspect for Leaks

• Visually inspect AC components (compressor, condenser, evaporator) and hoses for signs of oil or refrigerant leaks.
• If leaks are found, replace the affected components and ensure all connections are tight.