what exactly is the silver pipe that runs over the engine? The one that comes up on the driver's side and through the firewall on the passenger side. It's got a pump opening like that on a tire at the passenger side end. What does letting the air out do and what is it's function?

 

I believe you mean the A/C piping?

 

yeah, sounds like a/c to me. the "pump opening" as you refer to it sounds like a valve to service/recharge the a/c system

 

yeah, what they said