Heater Core

Remove and replace the heater core in a 1970 AMC Rebel Machine, requiring dash disassembly and coolant system draining.

Warnings

Tools required

Parts

• Heater core × 1 — Use OEM specification for 1970 AMC Rebel with A/C or non-A/C as applicable
• Heater core seals and gaskets × 1 — Heater box gasket kit
• Heater hose clamps × 4 — 5/8" and 3/4" worm gear clamps
• Engine coolant × 1 — Ethylene glycol 50/50 mix

Fluids

• Engine coolant (ethylene glycol) — 4 qt

Preparation

1. Ensure engine is completely cool (wait at least 2 hours after last operation)
2. Disconnect negative battery cable
3. Place protective covering over front seats and floor carpeting
4. Position drain pan under radiator petcock
5. Open radiator cap slowly to release any residual pressure
6. Drain cooling system completely via radiator petcock and engine block drain plug if equipped

Procedure

1. 1

   Disconnect heater hoses at firewall
   Locate the two heater hoses passing through the firewall on the passenger side of the engine bay. Use pliers to slide the hose clamps back several inches on each hose. Twist and pull the hoses off the heater core tubes. Have a drain pan ready as coolant will drain from the hoses and heater core. Cap or plug the hoses to minimize spillage.
2. 2

   Remove instrument cluster bezel
   Remove the screws securing the instrument cluster bezel (typically 4-6 screws around the perimeter). Carefully pull the bezel forward and away from the dash. Disconnect the headlight switch if attached to the bezel by pulling the knob, depressing the retaining tab, and unscrewing the retaining nut.
3. 3

   Remove instrument cluster
   Remove the screws securing the instrument cluster housing (typically 4 screws). Carefully pull the cluster forward enough to access the back. Disconnect the speedometer cable by unscrewing the knurled nut. Disconnect all electrical connectors from the back of the gauges, noting their positions. Remove the cluster from the vehicle.
4. 4

   Remove glove box and center lower dash panels
   Open the glove box and remove the screws securing it to the dash structure (typically 4-6 screws). Remove the glove box assembly. Remove any lower dash panels or trim pieces below the instrument cluster and on the passenger side to access the heater box. Remove all retaining screws and carefully pry panels free.
5. 5

   Disconnect heater control cables and vacuum lines
   Locate the heater control cables running from the control panel to the heater box. Note their positions and routing. Disconnect the cables at the heater box by removing retaining clips. Disconnect all vacuum lines from the heater box and any vacuum-operated blend doors or vents, labeling each line for reinstallation.
6. 6

   Disconnect blower motor wiring
   Locate the blower motor on the heater box (typically on the right side of the heater housing). Disconnect the electrical connector from the blower motor. If the blower motor resistor is accessible, disconnect its wiring as well.
7. 7

   Remove heater box mounting fasteners
   Locate and remove all nuts and bolts securing the heater box to the firewall and dash structure. This typically includes 3-4 nuts accessible from the engine bay side of the firewall at the heater core tube locations, and 4-6 bolts or screws inside the passenger compartment securing the box to the dash support. Support the heater box as you remove the final fasteners.
8. 8

   Remove heater box assembly
   Carefully maneuver the heater box assembly out from under the dash. This may require angling and rotating the box to clear the dash structure and steering column. Work slowly to avoid damaging surrounding components. Once free, place the assembly on a clean work surface.
9. 9

   Disassemble heater box and remove core
   On the work surface, remove the screws or clips securing the heater box halves together (typically 6-10 fasteners around the perimeter). Carefully separate the box halves, noting the position of any foam seals or blend door linkages. Lift the old heater core out of the housing, noting its orientation and any mounting brackets or seals.
10. 10

    Clean heater box and install new core
    Thoroughly clean the inside of both heater box halves, removing any debris, old leaves, or deteriorated foam. Inspect all blend doors and linkages for proper operation. Install new seals on the heater core if provided. Position the new heater core into the lower heater box half in the same orientation as the original, ensuring proper alignment of the core tubes with the box openings.
11. 11

    Reassemble heater box
    Position the upper heater box half onto the lower half, ensuring all blend door linkages are properly aligned and the heater core is correctly seated. Install all perimeter screws or clips, tightening evenly to avoid warping the housing. Verify that all blend doors move freely through their full range of motion.
12. 12

    Reinstall heater box assembly
    Maneuver the assembled heater box back into position under the dash, reversing the removal process. Align the heater core tubes with their firewall openings. Install and hand-tighten all mounting fasteners from inside the passenger compartment first, then access the engine bay and install the firewall nuts. Tighten all fasteners securely.
13. 13

    Reconnect all controls and wiring
    Reconnect the blower motor electrical connector and resistor wiring. Reconnect all heater control cables to their proper positions on the blend door linkages, adjusting cable tension as needed for proper operation. Reconnect all vacuum lines according to your labels or photos, ensuring secure connections.
14. 14

    Reinstall dash components
    Reinstall the lower dash panels, glove box, instrument cluster, and cluster bezel in reverse order of removal. Reconnect the speedometer cable and all gauge electrical connectors. Ensure all trim pieces are properly seated and all mounting screws are installed. Reconnect the headlight switch if applicable.
15. 15

    Connect heater hoses and refill coolant
    In the engine bay, slide new hose clamps onto the heater hoses. Push the hoses firmly onto the heater core tubes protruding through the firewall. Position clamps over the tube connections and tighten securely. Close the radiator petcock and engine block drain. Refill the cooling system with the proper 50/50 coolant mixture. Reconnect the negative battery cable.

Reassembly

1. All components are reinstalled during the main procedure steps
2. Ensure all dash trim pieces snap or screw into place firmly without forcing
3. Verify all heater control cables operate smoothly through their full range
4. Double-check that all vacuum lines are securely connected and not kinked

Verification

• Start the engine and allow it to reach normal operating temperature while monitoring for coolant leaks at the heater core connections
• Check coolant level in the radiator and top off as needed after initial warm-up and cool-down cycle
• Test heater operation by setting the temperature control to full hot and fan on high - airflow should be strong and hot
• Test all blend door positions (defrost, floor, panel) to ensure proper operation
• Verify no coolant odor in the passenger compartment and no wetness on the passenger floor
• Check for proper instrument cluster and gauge operation
• Inspect engine bay heater hose connections for any signs of coolant seepage after several heat cycles

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