AC/heater not blowing

I'm trying to figure out what the problem is on my AC on my 1999 7.3 powerstroke. The heater and AC worked a while back
Well we have changed
The blower motor resister
We jumped the blower motor and it wasn't locked up-came right on
And we replaced the control unit for the AC and heater
None of these things fixed the problem
Anyone know what I can do to fix this??
Thanks