Hey new to this site just a couple of quick questions. I have a 04 silverado crew cab Z71 w/ 5.3 and i still get a fair amount of air blowing through the vents even with the blower off there is also a thump and then hissing noise comming from the dash not sure if thare are related.

 

is it a repeated thump? sounds like your fresh air door could be out of sync. if thats the problem, it could possibly be fixed with a reprogram, unless the actuator has gone bad, in which case you'll need to replace it.

 

it will thump and hiss and about 5-10 seconds later it will thump and then hiss and keep doing this till i shut it off.

 

yeah sounds like you need a trip to the dealer for a reflash.

 

thanks got a couple other issues for them to look at, thanks again.

 

You will have air coming through the vents even with the blower motor turned off as far as I know. Every GM truck I have been in is like that.