GM Full-Size Trucks 1970-1979 Repair Guide

Heater Core

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REMOVAL & INSTALLATION




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.

1970-72 Vehicles

See Figure 1

WITHOUT AIR CONDITIONING
  1. Drain the cooling system and disconnect the negative battery terminal.
  2.  
  3. Remove the electrical connection at the blower.
  4.  
  5. Remove the heater hoses at the core tubes.
  6.  
  7. Remove the right front fender skirt. Remove enough screws so that the fender can be moved outward.
  8.  
  9. Working from under the instrument panel, remove the seal on the temperature door cable and disconnect the cable from the temperature door.
  10.  
  11. Pull the case away from the mounting studs after removing the retaining bolts.
  12.  
  13. Remove the core retainers and remove the core.
  14.  
  15. The installation procedure is the reverse of removal.
  16.  

WITH AIR CONDITIONING

Models with dealer installed air conditioning use the same procedure as those without air conditioning.

  1. Drain the coolant. Disconnect the negative battery cable.
  2.  
  3. Detach the heater hoses from the core tubes at the firewall.
  4.  
  5. Remove the stud nuts on the engine side of the firewall.
  6.  
  7. Remove the glove box.
  8.  
  9. Unplug the relay connector and remove the right ball outlet hose.
  10.  
  11. Remove the screw holding the panel outlet air distributor to the heater case. Remove the heater case retaining screws.
  12.  
  13. Pull the heater case away from the firewall; reach in and disconnect the resistor connector. Remove the resistor harness grommet and remove the harness.
  14.  
  15. Remove the heater case. Remove the core mounting straps. Reverse the procedure for installation.
  16.  

1973-79 Vehicles

See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: When installation is finished, fill the radiator to the proper level with coolant

  1. Disconnect the negative battery cable.
  2.  
  3. Detach the heater hoses at the core tubes and drain the engine coolant. Plug the core tubes to prevent spillage.
  4.  
  5. Remove the nuts from the distributor air ducts in the engine compartment.
  6.  
  7. Remove the glove compartment and door.
  8.  
  9. Disconnect the Air-Defrost and Temperature door cables.
  10.  
  11. Remove the floor outlet and remove the defroster duct-to-heater distributor screw.
  12.  
  13. Remove the heater distributor-to-instrument panel screws. Pull the assembly rearward to gain access to the wiring harness and disconnect the wires attached to the unit.
  14.  
  15. Remove the heater distributor from the truck.
  16.  
  17. Remove the heater core retaining straps and remove the core from the truck.
  18.  
  19. Installation is the reverse of removal. Be sure that the core-to-core and case-to-dash panel sealer is intact. Fill the cooling system and check for leaks.
  20.  

 
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