Ok well when I am driving down the highway and have the A/C running or just air blowing out and I give it quite a bit of gas for example going up a hill it starts to suck air in and quits blowing it out. At this point it sometimes makes a light knocking noise, but if I let off the gas the sucking goes away and the noise does to. Does anyone have any ideas on what is causing this? Thanks for all your help.

 

sounds like a vacuum problem.

 

X2 check that the vacumm hoses and vacuum can are not disconnected or damaged