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Eric, Automotive Repair Shop Manager
Category: Mercury
Satisfied Customers: 29713
Experience:  20+ yrs. experience as repair shop manager and technician.
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Need to replace heater core on 99 Grand Marquis. Need instructions

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Need to replace heater core on 99 Grand Marquis. Need instructions



Below are directions. It is a fairly big job has the entire dash has to come out:


  • If equipped, turn the air suspension service switch to the OFF position before raising the vehicle.
  • Drain the cooling system.
    • Remove or disconnect the following:

      Negative battery cable
    • Front seats
    • Carpeting
    • Rear airflow duct
    • Heater hoses
    • Remove the driver-s side air bag module by removing or disconnect the following:

      SRS module-to-steering wheel bolts, from both sides of the steering wheel.
    • SRS module and disconnect the electrical connector
    • Horn switch electrical connector
    • Remove the passenger-s side SRS module by removing or disconnecting the following:

      Open the glove box and disconnect the glove compartment isolator
    • Push inward on the 2 glove box door tabs and lower it
    • SRS module-s electrical connector
    • SRS module-to-instrument panel bolts and the module
    • Remove the instrument panel by removing or disconnecting the following:

      Speed control servo nuts and move the servo aside
    • Bolt and disconnect the left side bulkhead connector
    • Left side bulkhead connector from the dash panel
    • Windshield washer fluid reservoir screw, and position the reservoir aside
    • Blower motor electrical connector
    • Air conditioning pressure cut-off switch electrical connector
    • In-line electrical harness connector
    • Electronic Automatic Temperature Control (EATC) variable blower motor controller electrical connector
    • Right front wheel
    • Right front fender splash shield bolts and move the shield away from the cowl
    • Wiring harness from the evaporator case
    • Wiring harness from the cowl
    • Right side instrument panel lower insulator pushpins, disconnect the power point electrical connector, remove the courtesy lamp from the socket and remove the insulator
    • Unseat the wiring grommet and feed the wiring harness through the cowl
    • Cowl side trim panels and the windshield side garnish moldings from both sides
    • Locking clip and the Electronic Crash Sensor (ECS) module electrical connector
    • Antenna connector
    • Ground wire bolts from the right side
    • EATC hose at the evaporator housing
    • Bolt and disconnect the bulkhead connector from the right side
    • Pull the door weatherstrip seals away from the instrument panel on both sides
    • Tunnel brace trim cover
    • Climate control head vacuum harness connector
    • Instrument panel tunnel brace nuts and the brace
    • Ground wire bolts from the left side
    • Wiring harness connectors from the left side
    • Parking brake switch electrical connector
    1. Pry out the instrument panel defroster opening grille, disconnect the electrical connectors and the remove the grille.

    • Remove or disconnect the following:

      3 upper instrument panel screws
    • Instrument panel cowl side nut from both sides
    • Instrument panel cowl side bolt from the left side
    • Instrument panel
    • Windshield wiper mounting arm and the pivot shaft
    • Electrical connector and remove the upper cowl extension screw and the extension
    • Vacuum hoses and the wire harness connector from the evaporative emissions canister purge valve
    • Evaporative emissions purge valve nuts and the valve
    • Cowl side nut
    • Right side rear fender apron screws and reposition the apron
    • Evaporator housing nut and screw
    • Vacuum hoses and the wiring harness connectors
    • Plenum chamber-s lower flange nuts
    • Plenum chamber-s upper flange nut and the plenum chamber
    • Heater core cover-to-heater plenum chamber screws and the cover
    • Seal and the heater core


    Click image to see an enlarged view

    Fig. Exploded view of the instrument panel-Crown Victoria and Grand Marquis

    Click image to see an enlarged view

    Fig. Exploded view of the heater air plenum chamber, the evaporator housing and the air inlet duct

    Click image to see an enlarged view

    Fig. View of the heater core

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