Why does my Audi A5 heater only work on one side?

I've noticed that the heater in my Audi A5 only blows hot air on the driver's side, but the passenger side is always cold. What could be causing this imbalance and how can I fix it?

This is a common issue in Audi cars and is usually caused by a faulty temperature blend door actuator. It's responsible for controlling the air flow between hot and cold on each side of the car. You can try resetting it by disconnecting the car battery for a few minutes and then reconnecting. If that doesn't work, you may need to replace the actuator.