GM Buick/Oldsmobile/Pontiac/Full-Size 1975-1990 Repair Guide

Heater Core

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REMOVAL & INSTALLATION



See Figures 1, 2, 3, 4, 5, 6, 7, 8, 9

Models Without A/C
1975 AND 1976
  1. Disconnect the negative battery cable. Drain the radiator and disconnect the heater inlet and outlet hoses at the dash. Be careful not to damage the heater core if the hoses are stuck onto the core.
  2.  
  3. Disconnect the control wires from the defroster door and vacuum hose diverter door actuator, and the control cable from the temperature door lever.
  4.  
  5. Remove the 4 nuts securing the heater assembly to the firewall.
  6.  
  7. Remove the screw securing the defroster outlet tab to the heater assembly.
  8.  
  9. Remove the heater from the vehicle.
  10.  

To install:
  1. Make sure the heater assembly seal is in good condition.
  2.  
  3. Position the assembly onto the dash and tighten the retaining screws.
  4.  
  5. Reconnect the heater hoses, electrical connectors and negative battery cable. Refill the engine with coolant, start the vehicle and check for coolant leaks.
  6.  

1977 TO 1981
  1. Disconnect the negative battery cable and drain the cooling system.
  2.  
  3. Remove the heater hoses from the core tubes.
  4.  
  5. Disconnect the electrical connections.
  6.  
  7. Remove the front module cover screws, and remove the module assembly.
  8.  
  9. Remove the heater core from the module.
  10.  

To install:
  1. Make sure the heater assembly seal is in good condition.
  2.  
  3. Position the assembly onto the dash and tighten the retaining screws.
  4.  
  5. Reconnect the heater hoses, electrical connectors and negative battery cable. Refill the engine with coolant, start the vehicle and check for coolant leaks.
  6.  

1982 AND 1983
  1. Disconnect the negative battery cable and the Hoses from the core tubes. Plug them to avoid coolant loss.
  2.  
  3. On the engine side of the firewall, remove the heater core cover from the case.
  4.  
  5. Remove the core bracket and ground screw.
  6.  
  7. Lift out the core.
  8.  

To install:
  1. Make sure the heater assembly seal is in good condition.
  2.  
  3. Position the assembly onto the dash and tighten the retaining screws.
  4.  
  5. Reconnect the heater hoses, electrical connectors and negative battery cable. Refill the engine with coolant, start the vehicle and check for coolant leaks.
  6.  

1984 AND LATER
  1. Disconnect the negative battery cable, heater blower resistor wires and blower wires. Disconnect the heater core ground strap at the dash panel.
  2.  
  3. Drain the cooling system and then disconnect both heater hoses at the heater.
  4.  
  5. Remove the seven screws attaching the heater/blower case to the plenum and remove the heater/blower base.
  6.  
  7. Remove the four screws from the heater core shroud, and then remove the shroud and core assembly.
  8.  
  9. Separate the core from the shroud by removing the three screws and core mounting clamps and then separating the two.
  10.  

To install:
  1. Using sealer as necessary to prevent leaks at all joints and flanges.
  2.  
  3. Position the assembly onto the dash and tighten the retaining screws.
  4.  
  5. Reconnect the heater hoses, electrical connectors and negative battery cable. Refill the engine with coolant, start the vehicle and check for coolant leaks.
  6.  

Models with A/C
BUICK-1975 AND 1976
  1. Disconnect the negative battery cable, drain the radiator and disconnect the hoses from the core.
  2.  
  3. Disconnect the wires from the defroster door, diverter door and temperature door.
  4.  
  5. Remove the four nuts securing the core assembly to the dash.
  6.  
  7. Remove the screw securing the defroster outlet tab to the heater assembly.
  8.  
  9. Remove the core assembly.
  10.  

To install:
  1. Using sealer as necessary to prevent leaks at all joints and flanges.
  2.  
  3. Position the assembly onto the dash and tighten the retaining screws.
  4.  
  5. Reconnect the heater hoses, electrical connectors and negative battery cable. Refill the engine with coolant, start the vehicle and check for coolant leaks.
  6.  

OLDSMOBILE-1975 AND 1976
  1. Disconnect the negative battery cable and drain the radiator.
  2.  
  3. Remove the heater case securing nuts. Disconnect the heater hoses.
  4.  
  5. Remove the instrument panel trim pad.
  6.  
  7. Remove the heater case-to-firewall bolts from inside the vehicle.
  8.  
  9. Remove the bottom air duct.
  10.  
  11. Remove the instrument panel crash pad. Unfasten the leads from the clock and glovebox light.
  12.  
  13. Remove the upper right hand trim panel.
  14.  
  15. Separate the air distribution manifold and defroster duct from the heater case.
  16.  
  17. Remove the lower dash trim panel.
  18.  
  19. Lift out the heater case and disconnect the hoses and cables from it.
  20.  
  21. Remove the core from the case.
  22.  

To install:
  1. Install the core into the case.
  2.  
  3. Connect the hoses and cables to the case.
  4.  
  5. Install the lower dash trim panel.
  6.  
  7. Connect the air distribution manifold and defroster duct to the heater case.
  8.  
  9. Install the upper right hand trim panel.
  10.  
  11. Install the instrument panel crash pad. Connect the leads from the clock and glovebox light.
  12.  
  13. Install the bottom air duct.
  14.  
  15. Install the heater case-to-firewall bolts from inside the vehicle.
  16.  
  17. Install the instrument panel trim pad.
  18.  
  19. Install the heater case securing nuts. Connect the heater hoses.
  20.  
  21. Refill the radiator, connect the negative battery cable and check for leaks.
  22.  

PONTIAC-1975 AND 1976
  1. Disconnect the negative battery cable and drain the coolant.
  2.  
  3. Disconnect the hoses from the heater core. Plug the tubes to prevent damage to the carpeting on removal.
  4.  
  5. Remove the three nuts and one screw holding the core and case assembly in place.
  6.  
  7. Remove the glove box and upper and lower instrument panel trim plates.
  8.  
  9. Remove the radio.
  10.  
  11. Remove the cold air duct.
  12.  
  13. Remove the heater outlet duct.
  14.  
  15. Remove the screw holding the defroster duct to the heater case.
  16.  
  17. Disconnect the vacuum hoses from the diaphragm, and the air conditioner temperature cable at the heater case.
  18.  
  19. Remove the core from the case, after removing the 3 retaining screws.
  20.  

To install:
  1. Install the core into the case and tighten the 3 retaining screws.
  2.  
  3. Connect the vacuum hoses to the diaphragm, and the air conditioner temperature cable to the heater case.
  4.  
  5. Install the screw holding the defroster duct to the heater case.
  6.  
  7. Install the heater outlet duct.
  8.  
  9. Install the cold air duct.
  10.  
  11. Install the radio.
  12.  
  13. Install the glove box and upper and lower instrument panel trim plates.
  14.  
  15. Install the three nuts and one screw holding the core and case assembly in place.
  16.  
  17. Connect the hoses to the heater core.
  18.  
  19. Connect the negative battery cable and refill the coolant.
  20.  
  21. Start the engine and check for leaks.
  22.  

ALL MODELS-1977 AND LATER
  1. Disconnect the negative battery cable and drain the cooling system.
  2.  
  3. Disconnect the heater hoses.
  4.  
  5. Remove the retaining bracket and the ground strap. Disconnect the module rubber seal and module screen.
  6.  
  7. Remove the right windshield wiper arm.
  8.  
  9. Remove the diaphragm connections, the hi/blower relay, the thermal switch mounting screws, and all the electrical connections from the module top.
  10.  
  11. Remove the module top cover and remove the core.
  12.  

To install:
  1. Apply a strip of caulk-type sealer when installing the module top.
  2.  
  3. Install the core and module top cover.
  4.  
  5. Install the diaphragm connections, the hi/blower relay, the thermal switch mounting screws, and all the electrical connections to the module top.
  6.  
  7. Install the right windshield wiper arm.
  8.  
  9. Install the retaining bracket and the ground strap. Connect the module rubber seal and module screen.
  10.  
  11. Connect the heater hoses.
  12.  
  13. Connect the negative battery cable and refill the cooling system.
  14.  
  15. Start the engine and check for coolant and vacuum leaks.
  16.  



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Fig. Fig. 1: To remove the heater core, first remove the rubber seal



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Fig. Fig. 2: Remove the windshield washer nozzle attaching screw



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Fig. Fig. 3: Remove the washer nozzle from the heater module



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Fig. Fig. 4: Remove the module top attaching screws



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Fig. Fig. 5: Be sure to remove the module screws in the well



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Fig. Fig. 6: Remove the module cover



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Fig. Fig. 7: Remove the heater core hoses; be sure the cooling system is drained first



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Fig. Fig. 8: Remove the heater core retainer



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Fig. Fig. 9 Remove the heater core

 
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