why is my BMW 3 Series E90/E91’s AC compressor running constantly?

Solution

1. Preparation

• Gather necessary tools and parts.
• Disconnect the battery to ensure safety while working on electrical components.

2. Check Refrigerant Levels

• Use a refrigerant gauge to measure the low and high-pressure sides of the AC system.
• If levels are low, add the appropriate type of refrigerant (R134a for E90/E91 models).

3. Inspect and Replace AC Pressure Switch

• Locate the AC pressure switch, usually found on the receiver/drier or accumulator.
• Disconnect the electrical connector and remove the switch using a socket wrench.
• Install a new pressure switch and reconnect the electrical connector.

4. Inspect the AC Compressor Clutch

• Remove the drive belt by loosening the tensioner with a socket wrench.
• Inspect the compressor clutch for wear or damage.
• If the clutch is faulty, replace the entire compressor unit.

5. Reassemble and Recharge System

• Reinstall the drive belt, ensuring it is properly aligned.
• If refrigerant was added, ensure the system is fully charged according to manufacturer specifications.
• Reconnect the battery.