Ford 2003 Mustang Workshop Manual page 3057

Is there voltage present?
PINPOINT TEST A: INCORRECT/ERRATIC DIRECTION OF AIRFLOW
FROM OUTLET
A1 CHECK AIRFLOW FROM DEFROSTER OUTLETS
Key in START position.
Place the heater blower motor switch in the HI position and
rotate the function selector switch to each position.
Check for correct airflow from each function selector switch
position at engine idle and during engine speed acceleration.
Is there airflow from defroster outlets under all conditions?
A2 CHECK THE VACUUM SUPPLY HOSE
Key in OFF position.
Verify the vacuum supply hose is connected between the engine
manifold and the A/C vacuum check valve.
Is the hose connected?
A3 LEAK CHECK THE VACUUM SUPPLY HOSE
Test Step
Result / Action to
Take
Yes
GO to A2 .
No
If the airflow is from
defroster outlets in all
switch positions only
under engine speed
acceleration, GO to
A19 .
If the airflow is
incorrect under one or
more conditions, GO to
A13 .
If the airflow is correct
under all conditions,
RETURN to the
Symptom Chart.
Yes
GO to A3 .
No
RECONNECT the
hose. TEST the system
for normal operation.