How to Replace the Heater Core in a Mercury Cougarby ContributorUpdated November 07, 2017
Items you will need
Replacement heater core
Jack and jack stands
How to Replace the Heater Core in a Mercury Cougar. The good news in replacing an old Mercury Cougar's heater core is that you don't need to completely remove the instrument panel like most other cars. However, you do need to disconnect the heater ducts and the hoses for the engine compartment's vacuum source, but you can still accomplish this task with relative ease.
Removing the Old Core
Disconnect the Mercury Cougar's negative battery cable. Remove the center console from the interior. Disarm the car's air bag system and remove the bag's diagnostic monitor and bracket.
Take the heater outlet floor duct out of the car. Remove the screw holding the air transfer duct and push it into the outlet duct. Unscrew the screws retaining the outlet duct to the heater core cover and release the retaining tabs on each side to remove the duct.
Raise and support the Mercury Cougar, using multiple jackstands. Drain the engine coolant by removing the drain plug on the bottom of the radiator. Replace the drain plug after all the liquid flows into a clean container and disconnect the heater hoses from the core.
Withdraw the black vacuum supply hose from the vacuum source (you can now lower the vehicle). Disconnect the same hose from the air conditioner's vacuum reservoir tank.
Detach the heater core cover that holds the core by releasing the retaining tabs and removing the clips. Remove the dash panel seal, vacuum hose and heater core bracket from the cover.
Remove the heater core from the cover and the case seal from the core.
Installing the New Core
Install the replacement heater core into the cover with the case seal connected. Connect the heater core bracket, dash panel seal and vacuum hose onto the cover. Install the core cover into its compartment.
Put the vacuum supply hose back on to the air conditioner's vacuum reservoir tank by first raising the car once more. Connect the hose to the vacuum source in the engine compartment. Reconnect the heater hoses onto the core before lowering the vehicle.
Reinstall the heater outlet floor duct and connect it to the heater core cover. Reset and secure the transfer duct from the outlet floor duct.
Connect the air bag diagnostic monitor and bracket, along with the center console. Reconnect the negative battery cable and refill the cooling system with fresh coolant.
Start the Mercury Cougar and run it until it reaches the normal operating temperature. Check to make sure the repair was successful and there aren't any leaks in the system.