Overcharging your car's AC system can lead to a number of different symptoms. The most common symptom is the AC not blowing cold air. This is because the AC compressor is not cycling on and off correctly, which prevents the AC system from cooling the air. Other symptoms can include the AC system making strange noises, the AC system not turning on at all, or the AC system blowing hot air. If you notice any of these symptoms, it's important to take your car to a mechanic to have the AC system checked.