Component Tests
Heater Core
WARNING: Carbon monoxide is colorless, odorless and dangerous. If it is necessary to operate the engine with the vehicle in a closed area such as a garage, always use
an exhaust collector to vent the exhaust gases outside the closed area.
1.
NOTE:
Testing of returned heater cores reveals that a large percentage of heater cores are good and did not require replacement. If a heater core leak is suspected, the heater core
must be tested by following the plugged heater core component test before the heater core pressure test. Perform a system inspection by checking the heater system thoroughly as
GO to
G4
.
G2
CHECK THE A/C BLOWER MOTOR SPEED
Turn the function selector switch to the FLOOR position and the blower motor switch to the HI position.
Does the A/C blower motor operate?
Yes
CYCLE the blower motor switch from HI to LO several times. If the blower operates each time, ADVISE the
customer of proper system operation. If the blower does not operate correctly, REPLACE the blower motor switch.
TEST the system for normal operation.
No
GO to
G3
.
G3
CHECK THE BLOWER MOTOR SWITCH
Blower Motor Switch
Measure the resistance between the blower motor switch terminals in each switch position.
Switch Position Continuity Between Terminals
LO
None
Low medium
2 and 3
High medium
2, 3 and 4
HI
1, 2 and 4
Is the resistance between the specified terminals less than 5 ohms?
Yes
REPAIR Circuit 57 (BK). RETEST the system for normal operation.
No
REPLACE the blower motor switch. RETEST the system for normal operation.
G4
CHECK THE OTHER A/C BLOWER MOTOR SPEEDS
Turn the function selector switch to the FLOOR position and the blower motor switch to the LO position and then
to the next position.
Does the A/C blower motor operate in both positions?
Yes
INSPECT the harness connector at the blower motor switch. REPLACE the harness connector if damaged. If OK,
REPLACE the blower motor switch.
No
If the blower doesn't work in LO, REPLACE the A/C blower motor resistor.
If the blower works in LO, GO to
G5
.
G5
CHECK THE BLOWER MOTOR SWITCH CONNECTOR
Check to ensure the connector is correctly and securely connected to the blower motor switch.
Is the connector properly attached to the blower motor switch?
Yes
REPLACE the blower motor switch. RETEST the system for normal operation.
No
RECONNECT and CHECK the A/C blower motor operation.
Page 28 of 30
1999 F-150/250 Workshop Manual
8/16/2010
http://www.fordtechservice.dealerconnection.com/pubs/con...
