First, be sure you don't have one of the vacum actuated diaphrams in-line with the heater core lines. If you do, be sure it has vacuum, or not, accordingly.
There is a MAIN deflector piece just inside the fire wall entrance hole. The flap has two controller type diaphrams. With no vacuum you get little velocity and mostly cowl air, with some heater core blow by. With one or the other diaphram "activated" the flap either
lets air come straight from the fire wall hole into the next deflector (face/foot/deftrost), or it'll divert it to flow to/through the heator core and coninue on to just the floor or the defrost. i.e. no heat to the dash ducts.
You could just have a vacuum leak and crap wont happen at all.
If you have A/C with dash ducts (like me), pop off the box that deflects air to the different dash ducts. Just 4 screws and behind it is the MAIN deflector I spoke of.
There is all the issue of cowl versus reserculated air.
-I've reverse engineered the whole freakin' thing!
71' 3880# with me. Big Block 402, Merlin oval heads, 10.2:1CR, TH400, 3.73 posi,
1/8th: 8.2 @ 86.8mph
1/4: 12.7 @ 107.8mph (1.93 sixty foot)
--have pulled a 1.85 sixty foot (before street tires or course).
Picture of me roasting the tires and other guy stuff
Video of me staging (smoke of course)
[This message has been edited by BB_Mike (edited 09-17-2001).]