Originally Posted by lornaschinske
I have a similar one. It's to vent the bus on hot days so the windows don't blow out. Kinda like why I open a window on the Jeep just a crack. Started doing that after I had a window shatter in a very dark green car with black interior. Nights get very cool in the NC mountains but can/warm up nicely on a sunny day. Since then I leave a window open just a tiny crack. Enough to let expanding hot air out yet not let rain in.
I have sealed of our vent on the Blue Bird from the inside with spray foam and a piece of sheet metal. It was sucking our air conditioned air out of the bus since the vent was right at the front of the air conditioner.
This is how internet rumors get started.
I know that vehicle windows will sometimes shatter on very hot days, but it's NOT due to the interior air pressure "blowing out" the glass. The high temperatures can sometimes cause auto glass to shatter because tempered glass is made with high internal stresses that give it strength, but also ensure that when it does break, it breaks into a million little pieces instead of long, dangerous shards. A single, invisible flaw in the glass can cause it to become very brittle on a very hot day and anything could set off the chain reaction that causes the window to break.
No car is sealed so well that the difference in air pressure could cause the glass to break. Air leaks out through a thousand small cracks around the car, and a bus is no exception.
If a car were sealed well enough to trap the air inside with enough pressure differential to break the glass (have you ever tried to break a car window?), it would follow that using the heater on a cold day to warm the air temp in the car to forty degrees above the outside temperature would cause the windows to suck into the car, or at least create such a pressure differential that you'd never be able to open the door.
Science is your friend.