How to Remove the Heater Plenum on a 1984 Ford Mustang

The 1984 Ford Mustang´s heater plenum is located underneath the hood of the car, secured to the firewall. The heater plenum works in tandem with the heater core to supply hot air to the car´s interior (note that only vehicles without a factory-installed air-conditioning system have a heater plenum). The heater plenum can wear from continued use, cutting off the flow of warm air to the cabin of the car. The plenum is normally removed together with the heater core when warm air no longer blows through the vehicle´s heating vents.

Tools Used: Socket wrench, Screwdriver, Drip pan

Remove Heater Plenum

Disconnect the negative battery terminal with a socket wrench and disconnect the two heater cables from the passenger side firewall. Loosen the clamps that secure the cables through the firewall to disconnect them from the heater core in the cabin of the vehicle. Make sure to place a drip pan beneath the heater cables to catch any coolant that spills from the detached heater cables.

Lower the steering column and remove the instrument panel and instrument panel bezel. Use a screwdriver to remove the instrument panel´s mounting screws and then pull out the instrument panel, followed by the bezel. Remove the center dashboard panel and lower dashboard panel. Remove the two center console trim panels to expose the heater core housing. Use a screwdriver to remove the screws that secure the heater core cover. Pull the cover off and set it aside.

Pull the heater core out of the heater core housing and set it aside. Working under the hood of the vehicle again, locate the four bolts that secure the heater plenum to the firewall --- the bolts are next to the two heater hoses that were removed in Step 1. Use a socket wrench to detach the defroster plenum cable from the body of the heater plenum and then remove the four bolts that secure the plenum to the firewall. With the defroster cable and bolts removed, pull the heater plenum chamber away from the firewall.

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