021le

when coming to a stop, or at idle the a/c starts blowing from the defrost instead of the vents.

anyone have this issue?

when crusing on the highway its fine.

car has a 233/236 cam, and bolt ons.

any ideas?

021le

anyone?

RockinWs6

Low vacuum.........defrost is the default if there is no vacuum.

LilJayV10

iTrader: (39)

More than likely this is broken.

http://www.ebay.com/itm/Dorman-47150-Two-Port-Check-Valve-For-GM-Vacuum-Systems-Heater-Control-/200966353454?pt=Motors_Car_Truck_Parts_Accessories&hash=item2eca87322e&vxp=mtr
It's near of the HVAC box, rear passenger side valve cover.

Wild Willy

+1 on the low vacuum. Check your hoses for leaks, might be hard to hear.

spy2520

iTrader: (3)

Or a crack in that hard plastic hose that runs to the back of the intake, or a tear in the little boot at the end.