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how do i replace heater core or on 1996 gmc sonoma can i get diagram on this sight?


REMOVAL &



REMOVAL & INSTALLATION



1994-97 Vehicles

See Figure 1




Click image to see an enlarged view

Fig. Fig. 1: Exploded view of a common heater core and case assembly

  1. Disconnect the negative battery cable and properly drain the engine cooling system to a level below the heater core.
  2.  
  3. Disconnect the heater hoses from the core tubes near the cowl.
  4.  


The instrument panel carrier is designed not only to provide access to parts through removal of the carrier components, but the carrier will also tilt downward as a complete assembly to allow access from the top. If this is desired, remove the retainer screws along the top and bottom of the carrier assembly (refer to the figure). The instrument panel will then tilt as an assembly into the cab. It is necessary to unbolt and lower the steering column from the carrier to allow for maximum movement of the instrument panel.


  1. The instrument panel must be removed or repositioned for access to the heater core case. Unbolt and either tilt the instrument panel forward or disengage the instrument panel components and remove the panel from the vehicle. In most cases, tilting the panel forward should be sufficient for the necessary access, but if necessary remove the panel refer to

    in this guide.
  2.  
  3. Unfasten the heater core rear case retaining screws, then remove the rear case for access to the heater core.

  4.  
  5. Loosen the retainers and remove the heater core retaining straps.
  6.  
  7. Remove the heater core and seals.
  8.  


To install:

  1. Install the heater core and seals, taking care not to damage the core tubes when inserting them through the cowl.
  2.  
  3. Install and secure the core retaining straps.
  4.  
  5. Install the rear case and secure using the screws.
  6.  
  7. Reposition and secure the instrument panel and components. Tighten the cowl screws to 17 inch lbs. (1.9 Nm) and the lower instrument panel screws to 66 inch lbs. (7.5 Nm).

  8.  
  9. Connect the heater hoses to the core tubes.
  10.  
  11. Connect the negative battery cable, then properly refill the engine cooling system.
  12.  
  13. Run the engine at normal operating temperature, then check for leaks.

  14.  


1998-99 Vehicles
pick-up models

  1. Disconnect the negative battery cable.
  2.  




CAUTION
Never open, service or drain the radiator or cooling system when hot; serious burns can occur from the steam and hot coolant. Also, when draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantities. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.



  1. Drain the engine coolant into a suitable container.
  2.  
  3. Disconnect the heater hoses at the firewall in the engine compartment.
  4.  

  5. Remove the instrument panel assembly. Refer to

    of this repair guide for this procedure.

  6.  
  7. Remove the air inlet assembly as follows:

    1. If necessary, tag and disconnect the vacuum connectors.

    2.  
    3. Remove the air inlet studs, the inlet assembly and if necessary the gasket.
    4.  


  8.  
  9. Tag and disconnect all necessary vacuum lines.
  10.  
  11. From inside the engine compartment, remove the heater assembly studs.
  12.  
  13. Remove the blower motor resistor as follows:

    1. Unplug the resistor electrical connection.
    2.  
    3. Unfasten the screws and remove the resistor.

    4.  


  14.  
  15. Once the resistor is removed it will uncover a stud inside the heater core housing. Remove this stud.
  16.  
  17. Remove the rear case screws, the heater assembly and the seals.
  18.  


To install:

  1. Install the seals, the heater assembly and the rear case screws.
  2.  
  3. Install the stud inside the heater core housing and tighten to 17 inch lbs. (1.9 Nm).
  4.  
  5. Install the blower motor resistor as follows:

    1. Place the resistor in position and tighten the screws to 17 inch lbs. (1.9 Nm).
    2.  
    3. Attach the electrical connector to the resistor.
    4.  


  6.  
  7. Working inside the engine compartment, install the heater assembly studs. Tighten the studs to 17 inch lbs. (1.9 Nm).
  8.  
  9. Attach and disconnected vacuum lines.
  10.  
  11. Install the air inlet assembly as follows:

    1. If removed, install the inlet assembly gasket.

    2.  
    3. Install the inlet assembly and the studs. Tighten the studs to 40 inch lbs. (4.5 Nm).
    4.  
    5. Attach all unplugged vacuum connectors.
    6.  


  12.  
  13. Install the instrument panel assembly.
  14.  
  15. Attach the heater hoses to the core tubes at the engine compartment firewall.
  16.  
  17. Refill the engine cooling system.
  18.  
  19. Connect the negative battery cable, start the vehicle and check for coolant leaks.

  20.  


utility models

Be sure to consult the laws in your area before servicing the air conditioning system. In most areas, it is illegal to perform repairs involving refrigerant unless the work is done by a certified technician. Also, it is quite likely that you will not be able to purchase refrigerant without proof of certification.

Discharging, evacuating and charging the air conditioning system must be performed by a properly trained and certified mechanic in a facility equipped with refrigerant recovery/recycling equipment that meets SAE standards for the type of system to be serviced. If you don't have access to the necessary equipment, we recommend that you take your vehicle to a reputable service station to have the work done. If you still wish to perform repairs on the vehicle, have them discharge the system, then take your vehicle home and perform the necessary work. When you are finished, return the vehicle to the station for evacuation and charging. Just be sure to cap ALL A/C system fittings immediately after opening them and keep them protected until the system is recharged.

  1. Have the A/C system evacuated by a certified technician using approved equipment.
  2.  
  3. Disconnect the negative battery cable.

  4.  

  5. Remove the instrument panel. Refer to

    of this repair guide for this procedure.
  6.  
  7. Remove the cowls, unplug the washer lines from the hood.

  8.  
  9. Unplug the underhood lamp electrical, if equipped, then remove the hood.
  10.  
  11. Remove the antenna and the PCM.
  12.  




CAUTION
Never open, service or drain the radiator or cooling system when hot; serious burns can occur from the steam and hot coolant. Also, when draining engine coolant, keep in mind that cats and dogs are attracted to ethylene glycol antifreeze and could drink any that is left in an uncovered container or in puddles on the ground. This will prove fatal in sufficient quantities. Always drain coolant into a sealable container. Coolant should be reused unless it is contaminated or is several years old.



  1. Drain the coolant into a suitable container and remove the coolant recovery reservoir.
  2.  
  3. Disconnect the coolant hoses from the heater core at the firewall in the engine compartment.
  4.  
  5. Remove the right headlamp assembly. Tag and unplug all necessary electrical connections.

  6.  
  7. Remove right side fender.
  8.  
  9. Remove the battery, battery tray, and the wheel house panel.
  10.  
  11. Disconnect the A/C lines from the evaporator.

  12.  
  13. Unfasten the heater box shield retainers and remove the shield.
  14.  
  15. Unfasten the heater core mounting bolts from the engine compartment and remove the heater core fasteners from inside the vehicle.
  16.  
  17. With the aid of an assistant inside the vehicle, gently pry back on the heater box while removing the evaporator housing assembly to ensure clearance of the stud.
  18.  
  19. Remove the heater case, core and the seals.
  20.  


To install:

  1. Install the seals, core and case.
  2.  
  3. With the aid of an assistant inside the vehicle, pull forward on the heater box to make sure the evaporator core is in the correct position.

  4.  
  5. Install the heater case fasteners. Tighten the bolt/screw to 40 inch lbs. (4.5 Nm) and the stud to 40 inch lbs. (4.5 Nm).
  6.  
  7. Install the evaporator housing mounting bolts and tighten the bolt/screw to 40 inch lbs. (4.5 Nm).
  8.  
  9. Install the heater box shield and tighten the retainers to 19 inch lbs. (2.2 Nm).
  10.  
  11. Attach the A/C lines to the evaporator.
  12.  
  13. Install the wheel house panel, the battery tray and the battery. Do not connect the battery cables just yet.
  14.  
  15. Install the outer fender and attach all electrical connections that were disconnected.
  16.  
  17. Install the right headlamp assembly.

  18.  
  19. Attach the heater hoses to the heater core and install the coolant recovery reservoir.
  20.  
  21. Fill the cooling system.
  22.  
  23. Install the PCM and the antenna.
  24.  
  25. Install the hood, attach the hood lamp electrical connection and the washer lines. Install the cowls.
  26.  
  27. Install the instrument panel.
  28.  
  29. Connect the batter cables, start the vehicle and check for leaks.
  30.  


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