what causes musty smells in my BMW 3 Series E90/E91 (2005-2012) AC system

Solution

1. Preparation

• Tools Required: Screwdriver set, vacuum cleaner, cleaning cloths, AC disinfectant spray, OBD-II scanner.
• Disconnect the negative battery terminal to avoid electrical issues.

2. Cabin Air Filter Replacement

• Remove the cabin air filter cover using a screwdriver.
• Take out the old cabin air filter; inspect it for mold or dirt.
• Install a new cabin air filter, ensuring it is oriented correctly.

3. Clean the Evaporator Core

• Locate the evaporator core access point in the HVAC unit.
• Use a vacuum cleaner to remove any debris from the area.
• Spray an AC disinfectant cleaner onto the evaporator core and allow it to sit for the recommended time.

4. Clear the AC Drainage System

• Locate the AC drain tube under the vehicle.
• Use a flexible wire or compressed air to clear any blockages in the drain tube.
• Pour a small amount of water through the drain to ensure it flows freely.

5. Final Assembly

• Reattach the cabin air filter cover securely.
• Reconnect the negative battery terminal.
• Start the vehicle and allow the AC system to run for several minutes to circulate the disinfectant.