Door ventilator

[Ted]

Hi All,

In my car rear door, there is grilled area for ventilation purpose ( see picture 1). Originally it shall be fixed with a valve like window panel.(See picture 2). Currently I am not having that thing in both rear doors. What is the purpose of this particular thing? 

[Davy]

The interior of the car is essentially sealed. This is a pressure relief valve helps maintain proper pressure, temperature and to minimise fogging up on the windows. It also helps bleed out excess pressure when closing doors of the car, because a sudden spike in pressure occurs when doors are closed.

In most cars, the pressure relief valve is located behind the rear bumper, towards the side.