The heater core in your 1997 Cadillac STS uses a winding tube with tiny appendages to heat passing air, which is then delivered to the vehicle cabin via a fan. The heater core also enables the window defroster to do its job properly. As such, it is wise to change the heater core when the first warning signs of immanent failure appear. Otherwise, you will lose your defroster. This is particularly dangerous if you live in an area with high precipitation and cool air in the mornings and evenings.
Disconnect the negative battery cable using a ratchet and socket, then drain the coolant from the radiator by putting a drain pan below the drain plug of the radiator and releasing the plug with a ratchet and socket.
Label and remove the heater core hoses using a J-37097 hose clamp tool, then unscrew the sound insulator and glove compartment container from the passenger side of the firewall using a flat-head screwdriver.
Unbolt the programmer shield using a ratchet and socket, then detach the air mix valve connector, programmer vacuum and electrical connections by hand. Unscrew the heater core cover and the heater core using a Phillips screwdriver, then pull the heater core out.
Screw the new heater core and cover in place using a Phillips screwdriver, then reconnect the electrical connections, programmer vacuum, air mix valve connector and programmer shield.
Reconnect the heater core hoses and battery cable, then refill the radiator with coolant. Adjust the temperature to 90 degree Fahrenheit on the heater control panel, then wait for the setting arm to move to the highest heating position. Pull the rod from the setting arm retainer, then push the air mix valve to the highest air conditioning position. The arm should move freely.
Pull the rod up again to the highest heating position to prime the air mix valve, then adjust the temperature to 60 degrees Fahrenheit.
Reinstall the sound insulator, glove compartment container and heater hoses, then refill the radiator with coolant and reconnect the battery cable.
