98 S-10 no heat, defrost OK, A/c ok, manual HVAC

1998 S-10 with manual HVAC, 2WD, 4-cyl 5-speed.

A/C works fine.

Defrost works fine

Vent works fine.

Select heat (floor) and air will only blow out the defroster!

Actuators seem to be moving OK under the dash, no vac leaks found.

Have 2 trucks with same issue :banghead:

First check is for good full engine vacuum to heater controls.