Thanks Jim, but I have that same info in various FSM's. They all say the same thing, that it should draw hot air when cold, and modulate once the proper incoming air temp is reached. It even shows the 'vent' function venting into the air cleaner. Makes sense, as that lets the flap open. But it should also shut off the manifold vacuum. Mine vents at all times. It never shuts the hot air flap. Both sides just act like a huge vacuum leak. No response from Firebird Central, I think a phone call is in order.