If the functional test or other diagnosis indicates improper air delivery or a failure to shift modes when you move the mode knob, inspect the attachment of all the vacuum lines at the heater module and the control head.

Disconnect the vacuum line from the actuator at the crank pin. Inspect the air control valve travel and effort. If there is proper valve effort and travel, inspect the actuator at the heater module with the vacuum hose connected, and while moving the mode knob. Start the vehicle in order to assure an adequate vacuum. If the actuator does not move, inspect the vacuum line for damage, kinks, pinching, or a poor connection at the control assembly.