Blower Motor Resistor

Replace the blower motor resistor assembly that controls HVAC fan speeds on the 1970 AMC Rebel Machine.

Warnings

Tools required

Parts

• Blower motor resistor assembly × 1 — Use OEM specification or Standard Motor Products RU-8

Preparation

1. Ensure the engine is completely cool to the touch
2. Disconnect the negative battery cable to prevent electrical shorts
3. Turn the ignition key to OFF position and remove the key
4. Open the hood and secure it in the open position

Procedure

1. 1

   Locate the blower motor resistor
   From the engine compartment, locate the blower motor resistor on the firewall passenger side, near the blower motor housing. It will have a wire harness connector attached and is mounted to the heater plenum or evaporator case. The resistor block typically has cooling fins and is positioned where it receives airflow from the blower motor.
2. 2

   Disconnect the electrical connector
   Locate the wire harness connector attached to the resistor assembly. Press or pull the locking tab and carefully disconnect the connector from the resistor terminals. If the connector is corroded or stuck, gently wiggle it while pulling straight out. Do not pull on the wires themselves.
3. 3

   Remove the resistor mounting screws
   Remove the two mounting screws securing the resistor to the heater plenum using a 7/16 inch socket or Phillips screwdriver, depending on the fastener type. These screws may be difficult to access and may require working from an angle. Keep track of the screws as they are small and easily lost.
4. 4

   Extract the resistor assembly
   Carefully pull the resistor assembly straight out from the heater plenum. The resistor may be stuck due to corrosion or a sealing gasket. If resistance is felt, gently twist while pulling to break the seal. Avoid forcing it to prevent damaging the mounting flange on the plenum.
5. 5

   Inspect the mounting area and connector
   Examine the mounting surface on the plenum for corrosion, melted plastic, or damage. Check the wire harness connector terminals for signs of burning, melting, or corrosion. If the connector shows heat damage, it should be replaced along with the resistor. Clean the mounting surface with a wire brush or contact cleaner if corrosion is present.
6. 6

   Install the new resistor assembly
   Position the new blower motor resistor into the mounting hole in the heater plenum, ensuring the resistor coils are oriented into the airflow path inside the plenum. The resistor should fit snugly with the mounting flange flush against the plenum surface. Align the mounting screw holes carefully.
7. 7

   Secure the resistor mounting screws
   Install the two mounting screws and tighten them evenly in a cross pattern to secure the resistor. Tighten firmly but do not overtighten as this can crack the mounting flange or strip the threads in the plastic or sheet metal housing. The resistor should be firmly seated with no air gaps.
8. 8

   Reconnect the electrical connector
   Push the wire harness connector onto the resistor terminals until you hear or feel a positive click indicating the locking tab has engaged. Verify the connection is secure by gently tugging on the connector body, not the wires. Ensure all terminals are fully seated.
9. 9

   Reconnect the battery
   Reconnect the negative battery cable to the battery terminal and tighten securely. Ensure the cable connection is clean and tight.

Reassembly

1. Double-check that the resistor mounting screws are secure and the electrical connector is fully engaged
2. Verify no tools or parts have been left in the engine compartment

Verification

• Turn the ignition key to the RUN position without starting the engine
• Test the blower motor at all speed settings (LOW, MEDIUM-LOW, MEDIUM-HIGH, and HIGH) to verify all speeds function correctly
• Listen for smooth operation without unusual noises or hesitation between speeds
• Verify airflow strength increases appropriately with each speed setting
• Check that the blower motor does not run excessively hot during operation, which would indicate a problem with the new resistor or wiring

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