Also, I did forget to mention that there is a delay built into the system where you may not get cold or hot air right away..it'* about 45 seconds if I remeber, even if you leave the selector on hot or cold. Maybe you don't really have a problem, an dit is just the delay in the system.Has your car just recently started doing this or had it been like this all the time.
I found some info on the air mix actuator replacement procedure.
I found all of these by tying in "mix+actuator" (includingthe "+" symbol) in the "Search" function at the top of the Bonneville Club, (underneath the red Bonneville car) screen.
sign"Here is a write up donme by SSE Motorhead forseveral air problems. You (or your mechaninc) would want to follow the "Air Mix Actuator" instructions
Other random posts about the actuator:
There are many more if you do the "Search"