Heater core is leaking has a R-12 A/C system

Must replace the heater core. Its usually a very hard job that requires disassembly of the dash. If you insist on doing the job yourself, I suggest getting a repair manual from your local auto parts store so you can use it as a reference as you work. Here is a link to a video on a 98, yours will be very similar: http://www.youtube.com/results?search_query=1991+Pontiac+Bonneville+heater+core+replacement&sm=12

You can order the heater core at any Auto Supplier
that specializes in A/C, heater,radiator,etc parts,also
maybe an auto parts store

I will be sarcastic here. Anyone owning a corvette, should
be doing their own work

If I could buy a stingray brand new, at age 19 & do a frame up
restoration,bore the old 327 & sleeve it at 22, & rebuilt the trans,
without any help or knowledge,you should be able to install
a heater core.

2000-2005 Heater Core Replacement Instructions REMOVAL PROCEDURE

TOOLS REQUIRED
J 38185 Spring Hose Clamp Pliers

1. Drain the cooling system. Refer to Draining and Filling Cooling System in Cooling System.
2. Remove the fuel injector sight shield.
3. Position the J 38185 in order to remove the heater hose clamps.
4. Remove the heater hoses from the heater core.
5. Remove the left side sound insulator.
6. Remove the right side sound insulator.
7. Remove the air distributor duct screws (1,2). Due to the difficulty in the removal of the right side screw (2), it will not be necessary to install upon reassembly.
8. Remove the air distributor duct.
9. Remove the heater core heat shield screws.
10. Remove the heater core heat shield.
11. Remove the heater core cover screws (1).
12. Remove the heater core cover.
13. Remove the retaining screw and strap from the heater core.
14. Remove the heater core.


INSTALLATION PROCEDURE
NOTE: Refer to Fastener Notice in Service Precautions.

1. Install the heater core into the HVAC module using the attaching straps and screws. Tighten Tighten the screw to 1.4 N.m (12 lb in) .
2. Install the heater core cover.
3. Ensuring the seals at the front of dash are in the proper positions, install the heater core cover screws. Tighten Tighten the screws to 1.4 N.m (12 lb in) .
4. Install the heater core heat shield and screws (1). Tighten Tighten the screws to 1.4 N.m (12 lb in) .
5. Install the air distributor duct and the left screw (1). Ensure the right tab is seated properly. Tighten Tighten the screw to 1.4 N.m (12 lb in) .
6. Install the left side sound insulator.
7. Install the right side sound insulator.
8. Install the heater hoses and clamps using the J 38185.
9. Install the fuel injector sight shield.
10. Fill the cooling system. Refer to Draining and Filling Cooling System in Cooling System.

Hope this helps and just keep in mind that your feedback is important and I'll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa.

I have the shop manual & wiring book from Ford for your car. If interested, let me know. $25 plus postage.

this is a big job, time consuming. Is it leaking coolant?

Removal and Installation
NOTE: If a heater core leak is suspected, the heater core must be leak tested before it is removed from the vehicle.

1. Drain the cooling system. For additional information, refer to Section 303-03.

1. Position the front seats fully rearward.

1. Depower the supplemental restraint system. For additional information, refer to Section 501-20B.

1. Remove the wiper motor and pivot assembly. For additional information, refer to Section 501-16.

1. Remove the LH and RH windshield side garnish mouldings. For additional information, refer to Section 501-05.

1. Remove the LH and RH A-pillar lower trim panels. For additional information, refer to Section 501-05.

1. Disconnect the heater hoses from the heater core.

1. Lower the glove compartment.

1. Remove the 3 steering column opening panel lower bolts.
   • To install, tighten to 8 Nm (71 lb-in).

1. Remove the steering column opening panel cover.

1. Remove the steering column opening panel upper bolts.
   • To install, tighten to 8 Nm (71 lb-in).

1. Remove the steering column opening panel reinforcement.

1. Remove the 4 storage console pin-type retainers.

1. Remove the storage console.

1. Remove the rear seat floor duct adapter.

1. Remove the upper instrument panel finish panel.

1. Remove the LH lower instrument panel bolt.
   • To install, tighten to 12 Nm (9 lb-ft).

1. Remove the LH upper instrument panel bolt.
   • To install, tighten to 12 Nm (9 lb-ft).

1. Remove the 4 upper instrument panel bolts.

1. Remove the upper instrument panel cowl bolt.
   • To install, tighten to 5 Nm (44 lb-in).

1. Remove the 4 instrument panel center support brace bolts.
   • To install, tighten to 12 Nm (9 lb-ft).

1. Remove the LH instrument panel support bracket bolt.
   • To install, tighten to 12 Nm (9 lb-ft).

1. Loosen the RH instrument panel bolts one half of the bolt length, but do not completely remove the bolts.
   • To install, tighten to 12 Nm (9 lb-ft).

1. Working through the glove compartment opening, remove the RH instrument panel support bracket bolt.

1. Position the LH side of the instrument panel slightly away from the dash panel.

1. Remove the heater core and evaporator core housing support brace nut.

1. Remove the heater core and evaporator core housing support brace bolt.

1. Remove the heater core and evaporator core housing support brace.

1. Remove the 4 floor duct screws.

1. Remove the floor duct.

1. Remove the 7 heater core cover screws.

1. Detach the wire harness from the heater core cover.

1. Remove the heater core cover.

1. Remove the heater core.

1. To install, reverse the removal procedure.

1. Fill the engine cooling system. For additional information, refer to Section 303-03.

The only component inside the car that carries antifreeze is the heater core. I have not heard of any such problems with the year car you have. Take it to any radiator shop (or trusted repair shop) and ask them to pressurize the cooling system. If it doesn't hold pressure, you have a leak somewhere that should be apparent with pressure on the cooling system. It could be as simple as a loose clamp. If it were the heater core, you could feel the carpet where it touches the firewall. If it's wet and sweet smelling, you need a new heater core installed. Replacing the heater core requires quite a bit of disassembly and not something I would recommend for a typical backyard mechanic. Good luck.

Bad heater core you will need to replace it. About a 2 hour job, very easy to do:


Remove the HVAC module assembly. Refer to HVAC Module Assembly Replacement.
Remove the HVAC filter cover.
Remove the heater core/evaporator tube seals from the module.
Remove the heater core cover screws (1).
Remove the heater core retaining screws (1).
Remove the heater core retaining straps.
Remove the heater core.
Remove the rubber seals from the inlet/outlet pipes of the heater core.

Installation Procedure

Install rubber seals to the outlet/inlet pipes of the heater core.
Install the heater core to the module.
Install the heater core retaining straps.



Install the heater core retaining screws (1).
Install the heater core cover.



Install the heater core cover screws (1).



Install the heater core/evaporator tube seal from the module.
Install the HVAC filter cover.
Install the HVAC module assembly. Refer to HVAC Module Assembly Replacement.

SECTION 412-02: Heating/Defrosting 1998 Explorer/Mountaineer Workshop Manual REMOVAL AND INSTALLATION Heater Core Removal

1. NOTE: If a heater core leak is suspected, the heater core must be leak tested before it is removed from the vehicle. For additional information, refer to Section 412-00 .
   Drain the radiator. For additional information, refer to Section 303-03 .

1. Remove the heater water hoses.
   1. Squeeze the clamps and pull the hoses off.
   1. Disconnect the vacuum hose from the water control valve.

1. Remove the instrument panel. For additional information, refer to Section 501-12 .

1. Remove the A/C evaporator core housing. For additional information, refer to Section 412-03 .

1. Remove the A/C evaporator core housing. For additional information, refer to Section 412-03 .

1. Remove the powertrain control module (PCM). For additional information, refer to Section 303-14 .

1. Remove the PCM heat sink.
   1. Remove the ground strap screw.
   1. Remove the heat sink.

1. Remove the heater air plenum nuts from the engine side of the dash panel.

1. Remove the heater core.
   1. Remove the heater core cover to air plenum screws.
   1. Lift off the cover.

1. Remove the heater core (18476).

Inspect/Replace If it is necessary to remove the heater assembly, the cooling system must be drained before removing the heater core.
When a heater core leaks, a new heater core is installed or the old one repaired.
Heater Housing

• The heater housing is usually under the dash and must be removed to gain access to the heater core.
• Procedures for replacing the heater core vary with the year, make, and model of car. It threfore necessary to consult the manufacturer's repair manuals for the proper procedure for replacement.

The heater housing is disassembled to get to the heater core. Heater Core

• Remove the access panels(s) or the split heater/air conditioning case to gain acess to the heater core.
• Remove the heater coolant hoses.
• Remove the cable and/or vacuum control lines (if equipped).
• Remove the heater core securing brackets and/or clamps.
• Lift the core from the case. Do not use force. Take care not to damage the fins of the heater core when removing.
• To reinstall the heater core, reverse the removal steps.

When the heater core leaks and must be repaired or replaced, it is a very difficult and time-consuming job primarily because of the core's location deep within the firewall of the car. For this reason always leak test a replacement heater core before installation.

i don't know realy if there is a fuse (though i doubt it) but issues with heatting may be this will help.

If the carpet under the heater core is damp, or if antifreeze vapor or steam is coming through the vents, the heater core is leaking.
Remove it and install a new unit (most radiator shops will not repair a leaking heater core.
If the air coming out of the heater vents isn't hot, the problem could stem from any of the following causes:

• The thermostat is stuck open, previnting the engine coolant from warming enough to carry heat to the heater core. Replace the thermostat.
• There is a blockage in the system, Preventing the flow of coolant through heater core. Feel both heater hoses the firewall. They should be hot.if one of them is cold, there is an obstruction in one of the hoses or in the heater core,or the heater control valve is shut. Detach the hoses and back flush the heater core with a water hose. If the heater core is clear but circulation is impeded, remove the two hoses and flush them out with a water hose.
• If flushing fails to remove the blockage from the heater core, the coremust replaced.
  

If u have issues with heatting may be this will help.

1- If the carpet under the heater core is damp, or if antifreeze vapor or steam is coming through the vents, the heater core is leaking.Remove it and install a new unit (most radiator shops will not repair a leaking heater core.

1 - If the air coming out of the heater vents isn't hot, the problem could stem from any of the following causes:

• The thermostat is stuck open, previnting the engine coolant from warming enough to carry heat to the heater core. Replace the thermostat.
• There is a blockage in the system, Preventing the flow of coolant through heater core. Feel both heater hoses the firewall. They should be hot.if one of them is cold, there is an obstruction in one of the hoses or in the heater core,or the heater control valve is shut. Detach the hoses and back flush the heater core with a water hose. If the heater core is clear but circulation is impeded, remove the two hoses and flush them out with a water hose.
• If flushing fails to remove the blockage from the heater core, the coremust replaced.