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the heater core in a 1998 Cadillac is very tricky to replace. start with getting a pressure test to determine where the exact location of the leak is, it may not be the heater core. if you do decide to pull the dash apart to change the core make sure the battery is disconnected for at least an hour to allow the airbag system to discharge.
Thanks for choosing FixYa and welcome to the site. This model does not have the air bag option. If you choose to disengage, both airbags will be off. You may want to have it removed. I wouldn't choose to cut wires because it could be deployed. I do have some information on disengaging it if you are interested, but like I said, both airbags will be off.
The heater core does not look too hard to change. Here are the directions. It should take a skilled technician with all the correct tools about 1.4 hours to change....you might expect to spend 2 hours or a little more doing the job yourself.
The heater core is located on the driver's side of the HVAC housing, near the driver's right foot.
Removal - FRONT HEATER CORE
WARNING: On vehicles equipped with airbags, disable the airbag system before attempting any steering wheel, steering column, or instrument panel component diagnosis or service. Disconnect and isolate the battery negative (ground) cable, then wait two minutes for the airbag system capacitor to discharge before performing further diagnosis or service. This is the only sure way to disable the airbag system. Failure to take the proper precautions could result in accidental airbag deployment and possible personal injury or death.
WARNING: Refer to the applicable warnings and cautions for this system before performing the following operation. Failure to follow the warnings and cautions could result in possible personal injury or death.
Remove the silencer boot fasteners located around the base of the lower steering shaft from the dash panel so that it may be pushed aside.
Remove the brake lamp switch from its mounting bracket.
Disconnect the power brake booster input rod (push rod) from the pin on the brake pedal arm.
If equipped with power adjustable pedals, remove the adjustable pedal assembly.
NOTE: Take the proper precautions to protect the carpeting below the heater core from spilled engine coolant and have absorbent toweling readily available to clean up any spills.
Remove the heater core tubes.
Remove the two screws that secure the heater core mounting plate to the HVAC air distribution housing.
If NOT equipped with power adjustable pedals, pull the accelerator pedal upward (Accelerator Pedal) and push the brake pedal downward (Brake Pedal) for clearance to remove the heater core from the air distribution housing.
Remove the heater core by carefully pulling it straight out of the side of the air distribution housing.
Installation - FRONT HEATER CORE
If NOT equipped with power adjustable pedals, pull the accelerator pedal upward and push the brake pedal downward for clearance to install the heater core into the HVAC air distribution housing.
Install the heater core by carefully pushing it straight into the side of the air distribution housing.
Install the two screws that secure the heater core to the air distribution housing. Tighten the screws to 2 Nm (17 in. lbs.).
Install the heater core tubes.
If equipped with power adjustable pedals, install the adjustable pedal assembly
Connect the power brake booster input rod (push rod) to the pin on the brake pedal arm.
Install the brake lamp switch into its mounting bracket.
Install the silencer boot around the base of the lower steering shaft on the dash panel.
INSTRUCTIONS TO REPLACE HEATER CORE:
(1)Disarm the airbag system; (2)allow the cooling system to completely cool down; (3)using a thick cloth for protection, turn the radiator filler cap to the first stop; (4)step back and let the pressure release; (5)once the pressure has been released, completely drain the cooling system; (6) working within the engine compartment, loosen the ****,ps on the heater hoses at the engine compartment side of the firewall, twist the hoses and carefully sepseparate them from the heater core tubes; (7)plug or cap the heater core tubes to prevent coolant from spilling into the passenger compartment when the heater core is removed; (8)place a plastic sheet on the floor of the vehicle to prevent stains if the coolant spills; (9)remove the instrument panel; (10)remove the PCM heat sink and ground strap; (11)remove the heater plenum chamber; (12)separate the heater core from the heater plenum chamber; (13)installation is the reverse of the removal with the following additions; (a)fill the cooling system; (b)run the engine, check for leaks and test the heater.
ON VEHICLES EQUIPPED WITH AIRBAGS, DISABLE THE AIRBAG SYSTEM BEFORE ATTEMPTING ANY STEERING WHEEL, STEERING COLUMN, OR INSTRUMENT PANEL COMPONENT DIAGNOSIS OR SERVICE. DISCONNECT AND ISOLATE THE BATTERY NEGATIVE (GROUND) CABLE, THEN WAIT TWO MINUTES FOR THE AIRBAG SYSTEM CAPACITOR TO DISCHARGE BEFORE PERFORMING FURTHER DIAGNOSIS OR SERVICE. THIS IS THE ONLY SURE WAY TO DISABLE THE AIRBAG SYSTEM. FAILURE TO TAKE THE PROPER PRECAUTIONS COULD RESULT IN AN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSIBLE PERSONAL INJURY.
REVIEW THE WARNINGS AND CAUTIONS IN THE FRONT OF THIS SECTION BEFORE PERFORMING THE FOLLOWING OPERATION.
Remove the foam gasket surrounding the core tubes. NOTE: Notice the orientation of the irregularly shaped gasket on the tubes. The gasket must be placed correctly to ensure proper sealing against the body during reinstallation
Remove the screws and retainers that secure the heater core and tubes to the HVAC housing.
Remove the mode door actuator if necessary for clearance to remove the core.
Lift the heater core straight up and out of the HVAC housing.
When replacing individual tubes, loosen and remove the round tube-to-core clamp, and pull tube from core.
Any kinks or sharp bends in the refrigerant plumbing will reduce the capacity of the entire air conditioning system. Kinks and sharp bends reduce the flow of refrigerant in the system. A good rule for the flexible hose refrigerant lines is to keep the radius of all bends at least ten times the diameter of the hose. In addition, the flexible hose refrigerant lines should be routed so they are at least 80 millimeters (3 inches) from the exhaust manifold.
High pressures are produced in the refrigerant system when the air conditioning compressor is operating. Extreme care must be exercised to make sure that each of the refrigerant system connections is pressure-tight and leak free. It is a good practice to inspect all flexible hose refrigerant lines at least once a year to make sure they are in good condition and properly routed.
When installing individual tubes, insert tube into core ensuring that tube O-ring is seated in core and not pinched. Hold tube in seated position while installing the round tube-to-core clamp. NOTE: The round tube-to-heater-core clamp should be left loose enough to turn the tube in the core. Position the core in the housing, and then tighten the tube-to-heater-core clamp after orienting the tubes to the molded HVAC housing.
Lower the heater core into the HVAC housing.
Install the mode door actuator, if removed from housing for core removal.
Position the retainers over the heater core tubes. Install and tighten the screws that secure the heater core and retainers to the HVAC housing. Tighten the screws to 2.2 Nm (20 in. lbs.) . NOTE: The grounding strap is to be attached to the lower heater core tube retainer.