Simple enough question, but one which I don't know the answer too. Anyone know where this is located on a 78 z28?

in the inlet side of the evaporator core I am pretty sure

Can you take a picture of the front of the evap. case? Some variation in the type of control and location of the parts on these cars. If it has the standard orifice it should be in the small line where it connects to the evaporator at the firewall. Careful pulling it out, sometimes will break off, and big trouble then.

Here we are http://thumb15.webshots.net/t/85/85/9/35/65/2900935650086971775gwVbFY_th.jpg (http://good-times.webshots.com/photo/2900935650086971775gwVbFY)