dust/cake in between the fan and heatsink blowing compressed air into it will push it back into the fan and blow around inside the laptop. Usually there are screws holding on your keyboard remove those and take it off this should allow some access to the fan and heatsink you may have to take it apart to access the chuck blocking your airflow. The thickest chuck I have ever found was about 5mm thick blocking the whole heatsink fromt eh air the fan was blowing.