With HVAC System - Manual

1. Air flow out of the defroster duct only is an indication of no vacuum present at the Heater and A/C Solenoid Assembly.
2. Check manifold vacuum at the Black hose from the Engine on the Vacuum Tank.
^ If vacuum is not present, check the hose back from the Engine Vacuum Source.
^ If vacuum is present, check for vacuum at the Black hose at the Heater and A/C Control Head. If there is no vacuum at the Heater and A/C Control Head, replace the Vacuum Tank.
3. Check the operation of the Temperature Valve by moving the temperature lever rapidly back and forth several times. Listen for the valve to strike the stop at each end of its travel. If the sound indicates that the valve is not fully closing or opening, check the mechanical linkage between the valve and the Temperature Lever.

^ Refer to the A/C System Check for a guide to normal operation and diagnostic references.
^ Check for a broken (or partially broken) wire inside of the insulation which could cause system failure but prove "GOOD" in a continuity/voltage check.
^ Check for proper installation of aftermarket electronic equipment which may affect the integrity of other systems.