Ford 2003 Mustang Workshop Manual page 3063

Does the vacuum control motor hold a vacuum?
A20 CHECK THE VACUUM CONTROL MOTOR INSTALLATION
Key in OFF position.
Check the attachment of the vacuum control motor arm to
damper door.
Is the vacuum control motor arm attached to the door or
door crank arm?
PINPOINT TEST B: INSUFFICIENT, ERRATIC, OR NO HEAT
B1 CHECK FOR CORRECT ENGINE COOLANT LEVEL
Key in OFF position.
Check the engine coolant level when hot and cold.
Is the engine coolant at the correct level (hot/cold) as
indicated on the engine coolant recovery reservoir?
B2 CHECK FOR HOT WATER TO THE HEATER CORE INLET
HOSE
WARNING: The heater core inlet hose will become
too hot to handle and may cause serious burns if the
system is working correctly.
Key in START position.
Allow the engine to reach normal operating temperature.
Feel the heater core inlet hose.
Test Step
Yes
REPAIR or INSTALL a
new damper door.
TEST the system for
normal operation.
No
CONNECT the vacuum
control motor arm to
the door and check
operation. TEST the
system for normal
operation.
Result / Action to Take
Yes
GO to B2 .
No
GO to B3 .
Yes
GO to B4 .
No
TEST the engine cooling
system for correct
operation. REFER to
Section 303-03A or Section
303-03B .