HP EliteBook 850 G1 Notebook PC - Manual (Page 24)

Component Description
(3) Service door release lock Locks the service door.
(4) Vents (3) Enable airflow to cool internal components.
NOTE: The computer fan starts up automatically to
cool internal components and prevent overheating. It
is normal for the internal fan to cycle on and off during
routine operation.
14 Chapter 2 Getting to know your computer