Blower Motor Control Module

This procedure covers removal and replacement of the blower motor control module (resistor assembly) on a 1972 Ford F-100 with 302ci V8, which controls heater/AC fan speeds.

Warnings

Tools required

Parts

• Blower motor resistor assembly × 1 — Use OEM specification
• Wire connector (if corroded) × 1 — Use OEM specification

Preparation

1. Park vehicle on level surface and engage parking brake
2. Allow heater/AC system to cool completely if recently operated
3. Disconnect negative battery terminal and secure cable away from battery post
4. Position work light to illuminate passenger side footwell area under dashboard

Procedure

1. 1

   Access the blower motor resistor location
   The blower motor resistor is located on the heater housing under the passenger side dashboard. From inside the cab, position yourself in the passenger footwell and look upward toward the firewall. The resistor assembly is mounted to the heater case with the wire harness connector facing downward.
2. 2

   Disconnect the resistor wire harness
   Locate the wire harness connector attached to the resistor assembly. Press the locking tab or squeeze the connector sides (depending on style) and pull the connector straight off the resistor terminals. If connector is corroded or stuck, carefully wiggle while pulling. Do not force or bend terminals.
3. 3

   Remove resistor mounting screws
   Remove the 2 mounting screws securing the resistor assembly to the heater case using a Phillips screwdriver or 1/4" socket. These screws are typically sheet metal screws approximately 1/2 inch long. Support the resistor with your other hand as you remove the final screw to prevent it from falling.
4. 4

   Extract the resistor assembly
   Carefully pull the resistor assembly straight out from the heater case opening. The resistor has metal cooling fins that protrude into the air duct. Guide these fins out carefully to avoid bending. If resistance is felt, check that both mounting screws have been fully removed.
5. 5

   Inspect heater case opening and wire connector
   Examine the opening in the heater case for debris, leaves, or obstructions that could block airflow over the new resistor. Clean if necessary. Inspect the wire harness connector terminals for corrosion, burning, or damage. Clean terminals with electrical contact cleaner or wire brush if corroded. Replace connector if terminals are melted or damaged.
6. 6

   Install new resistor assembly
   Position the new resistor assembly with the cooling fins aligned with the heater case opening. Guide the fins into the air duct carefully, ensuring proper seating. The mounting screw holes should align with the threaded holes in the heater case. Push the resistor firmly into place until the mounting flange is flush against the heater case.
7. 7

   Install mounting screws
   Install the 2 mounting screws through the resistor flange into the heater case. Start both screws by hand to ensure proper threading. Tighten screws snugly but do not overtighten as the resistor flange and heater case are both relatively thin materials. Alternate between screws for even seating.
8. 8

   Reconnect wire harness
   Push the wire harness connector firmly onto the resistor terminals until the locking tab clicks into place. Ensure the connector is fully seated and cannot be pulled off without depressing the locking tab. Verify that all terminal pins are properly engaged.
9. 9

   Reconnect battery and test operation
   Reconnect the negative battery terminal. Turn the ignition key to the RUN position (engine does not need to be started). Test all blower motor speed settings (typically LOW, MEDIUM, and HIGH) to verify proper operation at each speed. Each setting should produce a noticeably different fan speed. Listen for unusual noises or verify no speeds are inoperative. Verified detail (1972 F-100 blower motors typically had 3 speeds (LOW, MEDIUM, HIGH), not 4 speed settings as described.): Test all blower motor speed settings (typically LOW, MEDIUM, and HIGH) to verify proper operation at each speed.

Reassembly

1. No disassembly of other components should be necessary for this procedure
2. Ensure all wire connections are secure and battery terminal is tight

Verification

• Test all blower motor speed settings with ignition on to confirm proper operation
• Verify each speed setting produces appropriate fan speed with no unusual noises
• Check that blower motor shuts off completely when switch is in OFF position
• Confirm no burning smell or excessive heat from resistor area during 5-minute test run

More procedures for this vehicle