Chevrolet Full-size Cars 1968-1978 Repair Guide

Heater Core

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REMOVAL & INSTALLATION





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Fig. Fig. 1 Exploded view of the heater housing and core mounting



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Fig. Fig. 2 Heater hose routing found on L6 and V8 engines

1968-71 Models

It is not necessary to discharge the air conditioning system to replace the heater core.

  1. Disconnect the negative battery cable.
  2.  
  3. Drain the cooling system.
  4.  


CAUTION
When draining the coolant, keep in mind that cats and dogs are attracted by the ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

  1. Disconnect the heater hoses from the heater core at the firewall.
  2.  
  3. Remove the nuts from the heater distributor studs protruding through the firewall on the engine side.
  4.  
  5. Remove the glove compartment door and inner tray.
  6.  
  7. Under the dashboard, remove the five center duct hoses, duct cables, center duct-to-selector duct screw and the center duct.
  8.  
  9. From inside the vehicle, drill out the lower case stud using a 1 / 4 " drill.
  10.  
  11. Remove the center floor air duct.
  12.  
  13. Remove the firewall screws and pull the selector from the firewall.
  14.  
  15. Disconnect and tag all wires, vacuum lines and cables attached to the assembly. Remove the heater assembly from the vehicle.
  16.  

It is very important to tag all cables and vacuum lines during removal. Failure to do so, may cause improper operation of the heater and/or air conditioning systems.

  1. Scribe the temperature door camming plate-to-selector duct relationship and remove the plate.
  2.  
  3. Remove the heater core and core housing from the selector duct.
  4.  

To install:

  1. Before installation, clean out all debris and coolant from the heater casing.
  2.  
  3. Match the new heater core to the old one to insure a proper fit.
  4.  
  5. Attach the heater core and housing to the selector duct.
  6.  
  7. Align the marks on the temperature door plate and selector duct and install the plate.
  8.  
  9. Install the heater assembly in the vehicle and connect all of the hoses, cables and vacuum lines according the way they are tagged.
  10.  
  11. Install the inside firewall mounting screws and center floor air duct.
  12.  
  13. Install the remaining hoses and air ducts.
  14.  
  15. Install the glove compartment tray and door.
  16.  
  17. On the engine side of the firewall, install the two outer heater assembly mounting screws.
  18.  
  19. Check the condition of the heater hoses and replace them if necessary. Connect the hoses to the heater core at the firewall.
  20.  
  21. Fill the cooling system, run the engine and check the heater operation.
  22.  

1972-76 Models
  1. Disconnect the negative battery cable. Drain the cooling system. It is not necessary to evacuate the air conditioning refrigerant.
  2.  
  3. Disconnect the air conditioning compressor clutch electrical connector.
  4.  
  5. Disconnect and tag the vacuum line from the vacuum check valve and push the grommet through the firewall into the passenger compartment.
  6.  
  7. Disconnect the heater hoses at the firewall.
  8.  


CAUTION
When draining the coolant, keep in mind that cats and dogs are attracted by the ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

It is a good idea to seal off the hose connections at the heater core. Although the cooling system is drained, there will still be some coolant left in the core. The twisting and turning sometimes required to remove the core may cause the remaining coolant to leak out on the floor and seats.

  1. Remove the three screws and nuts retaining the heater and selector duct. The inner fender must be loosened and pulled out from the firewall to gain access to one screw.
  2.  
  3. Remove the lap cooler assembly.
  4.  
  5. Remove the glove compartment.
  6.  
  7. Remove the floor outlet duct and dash panel pad.
  8.  
  9. Disconnect the distributor duct hoses and connector.
  10.  
  11. Remove the duct from the selector.
  12.  
  13. Loosen the defroster duct and move it to provide access to the selector and core assembly.
  14.  
  15. Disconnect the temperature door cable.
  16.  
  17. Separate the inline vacuum connector and the outside air diaphragm line.
  18.  
  19. Lift the heater and air selector duct out as an assembly.
  20.  
  21. Remove the retaining screws and remove the heater core from the selector.
  22.  

To install:

  1. Before installation, clean out all coolant and debris that may be inside of the casing.
  2.  
  3. Match up the new and old heater cores to insure a proper fit.
  4.  
  5. Install the heater core in the selector and install the retaining screws.
  6.  
  7. Install the heater and the air selector duct as an assembly in the vehicle.
  8.  
  9. Connect the inline vacuum connector and outside air diaphragm line.
  10.  
  11. Connect the temperature door cable. Install the distributor and defroster ducts, and hoses.
  12.  
  13. Install the floor outlet duct and dashboard pad.
  14.  
  15. Install, the glove compartment and lap cooler assemblies.
  16.  
  17. Install the outside mounting screws and reattach the fenderwell to the firewall.
  18.  
  19. Connect the heater hoses, vacuum lines and compressor clutch wire.
  20.  
  21. Fill the cooling system, connect the negative battery cable, run the engine and check the heater operation, when the engine reaches normal operating temperature.
  22.  

1977-78 Models
  1. Disconnect the negative battery cable. Drain the cooling system then, disconnect the hoses from the heater core. Plug the hoses and the core.
  2.  


CAUTION
When draining the coolant, keep in mind that cats and dogs are attracted by the ethylene glycol antifreeze, and are quite likely to drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantity. Always drain the coolant into a sealable container. Coolant should be reused unless it is contaminated or several years old.

  1. Remove the diagnostic connector plug to heater case screws.
  2.  
  3. Disconnect and tag the connectors from the blower motor, resistor, blower relay and the thermostatic switch.
  4.  
  5. Remove the air conditioning wiring harness retainer from the blower case shroud.
  6.  
  7. Remove the module screen (leaf screen) assembly screws and remove the screen.
  8.  
  9. Remove the upper case half to lower case half cowl attaching screws. Two of these screws are inside the air intake at the case separation point.
  10.  
  11. Remove the thermostatic switch by removing the electrical connector, the switch attaching screws and the small tube running from the switch to the evaporator inlet pipe. To remove the small pipe, remove the insulation at the evaporator inlet pipe and loosen the two clamps. When you reinstall this line make sure the line is replaced in its original position.
  12.  
  13. Remove the evaporator inlet pipe support bracket.
  14.  
  15. Remove the heater-evaporator core case cover, making sure you do not damage the sealer.
  16.  
  17. Remove the heater core to case attaching screw and pull up firmly to release the core from the spring loaded clip. Remove the heater core from the vehicle.
  18.  

To install:

  1. Line up the core base with the clip at the bottom of the case before you insert the core. The top retaining bracket will line up with the hole at the top of the core when properly seated.
  2.  
  3. Install the new core in the spring loaded clip and install the core to case mounting screws.
  4.  
  5. Install the case cover making sure that cover is completely seated in the sealer.
  6.  
  7. Install the evaporator inlet pipe support bracket.
  8.  
  9. Install the small pipe from the thermostatic switch to the evaporator pipe in the exact position as before removal. Wrap the sealer around the pipe.
  10.  
  11. Install the thermostatic switch and mounting screws. Connect the switch wiring.
  12.  
  13. Install the upper case half to the lower half and tighten the mounting screws.
  14.  
  15. Install the leaf screen. Install the wiring harness in the retainer on the casing.
  16.  
  17. Connect the wiring and diagnostic connector at the casing.
  18.  
  19. Connect the heater hoses to the core and fill the cooling system.
  20.  
  21. Connect the negative battery cable, run the engine and check the heater operation.
  22.  

 
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