Technical Car Experts Answers everything you need: How to replace Heater core on 2000 mercury marquis?

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This heater core replacing guide is similar also for other car models
Ford Crown Victoria, Mercury Grand Marquis, Marauder, Lincoln Town Car.

The procedure is as follows :----

Removal & Installation

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

Fig. View of the instrument panel finish panels

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

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

Fig. View of the heater core

Fig. Exploded view of the instrument panel-Town Car

To install:

Install or connect the following:

Seal and the heater core
Heater core cover and the cover-to-heater plenum chamber screws
Plenum chamber and the plenum chamber-s upper flange nut
Plenum chamber-s lower flange nuts
Vacuum hoses and the wiring harness connectors
Evaporator housing nut and screw
Right side rear fender apron and the apron screws
Cowl side nut
Evaporative emissions purge valve and the valve nuts
Vacuum hoses and the wire harness connector to the evaporative emissions canister purge valve
Electrical connector; then, install the upper cowl extension screw and the extension
Windshield wiper mounting arm and the pivot shaft

Install the instrument panel by installing or connecting the following:

Instrument panel
At the left side, install the instrument panel cowl side bolt
Instrument panel cowl side nut on both sides
3 upper instrument panel screws
Electrical connectors and the install the instrument panel defroster opening grille
Parking brake switch electrical connector
Wiring harness connectors on the left side
Ground wire bolts on the left side
Instrument panel tunnel brace and the brace nuts
Climate control head vacuum harness connector
Install the tunnel brace trim cover.
Door weatherstrip seals to the instrument panel on both sides
Bulkhead connector and tighten the bolt on both sides
EATC hose at the evaporator housing
Ground wire bolts on the right side
Antenna connector
ECS module electrical connector and the locking clip
Cowl side trim panels and the windshield side garnish moldings on both sides
Feed the wiring harness through the cowl and seat the wiring grommet
Right side instrument panel lower insulator, connect the power point electrical connector, install the courtesy lamp to the socket and secure the insulator with pushpins
Wiring harness from the cowl
Wiring harness to the evaporator case
Right front fender splash shield and the shield bolts
Right front wheel
EATC variable blower motor controller electrical connector
In-line electrical harness connector
Air conditioning pressure cut-off switch electrical connector
Blower motor electrical connector
Windshield washer fluid reservoir and the reservoir screw
Left side bulkhead connector to the dash panel
Left side bulkhead connector and tighten the bolt
Speed control servo and the servo nuts
Right SRS module and torque the module-to-instrument panel bolts to 62-97 inch lbs. (7-11 Nm)
Right SRS module electrical connector
Glove compartment isolator
Glove box door
Horn switch electrical connector
Electrical connector and install the left SRS module
Left SRS module-to-steering wheel bolts on both sides of the wheel, and torque the bolts to 90-122 inch lbs. (10-14 Nm)
Rear airflow duct
Carpeting
Front seats
Heater hoses

Refill the cooling system.

Connect the negative battery cable.

Operate the engine to normal operating temperature. Check the climate control operation and check for leaks.

Town Car

Disconnect the negative battery cable.

Drain the cooling system and disconnect the heater hoses from the heater core tubes. Plug the hoses and the heater core tubes to prevent coolant leakage.

Remove the 3 nuts located below the windshield wiper motor attaching the left end of the plenum to the dash panel. Remove the 1 nut retaining the upper left corner of the evaporator case to the dash panel.

Disconnect the vacuum supply hose(s) from the vacuum source. Push the grommet and vacuum supply hose(s) into the passenger compartment.

Remove the right and left lower instrument panel insulators.

On 1988-93 vehicles:
1. Remove the 3 glove compartment hinge screws, disconnect the check arms and remove the glove compartment. Loosen the right door sill plate and remove the right side cowl trim panel. Remove the bolt attaching the lower right end of the instrument panel to the side cowl. Remove the instrument panel pad as follows:
2. Remove the 2 screws attaching the pad to the instrument panel at each defroster opening. Be careful not to drop the screws into the defroster openings.
3. Remove the one (shouldered) screw attaching each outboard end of the pad to the instrument panel.
4. Remove the line of screws attaching the lower edge of the pad to the instrument panel. Pull the instrument panel pad rearward and remove it from the vehicle.

On 1988-89 vehicles:
1. Remove all instrument panel mounting screws and pull the instrument panel back as far as it will go without disconnecting any wiring harnesses.
2. Make sure the nuts attaching the instrument panel braces to the dash panel are removed.
3. Loosen the right door sill plate and remove the right side cowl trim panel.
4. Disconnect the temperature control cable from the ATC sensor. Disconnect the vacuum harness line connector from the ATC sensor harness and disconnect the electrical connector from the ATC servo connector.

On 1990-00 vehicles:
1. Remove the cross body brace and disconnect the wiring harness from the temperature blend door actuator.
2. Disconnect the ATC sensor tube from the evaporator case connector.

Disconnect the vacuum jumper harness at the multiple vacuum connector near the floor air distribution duct. Disconnect the white vacuum hose from the outside-recirculating door vacuum motor.

Remove the 2 hush panels.

Remove 1 plastic push fastener retaining the floor air distribution duct to the left end of the plenum. Remove the left screw and loosen the right screw on the rear face of the plenum and remove the floor air distribution duct.

Remove the 2 nuts from the 2 studs along the lower flange of the plenum.

Carefully move the plenum rearward to allow the heater core tubes and the stud at the top of the plenum to clear the holes in the dash panel. Remove the plenum from the vehicle by rotating the top of the plenum forward, down and out from under the instrument panel. Carefully pull the lower edge of the instrument panel rearward, as necessary, while rolling the plenum from behind the instrument panel.

On 1988-1989 vehicles, remove the ATC servo from the plenum.

Remove the 4 retaining screws from the heater core cover and remove the cover from the plenum assembly. Pull the heater core and seal assembly from the plenum assembly.

To install:

Carefully install the heater core and seal assembly into the plenum assembly. Visually check to ensure that the core seal is properly positioned. Position the heater core cover and install the 4 retaining screws.

On 1988-1989 vehicles, install the ATC servo on the plenum.

Route the vacuum supply hose through the dash panel and seat the grommet in the opening.

Position the plenum under the instrument panel with the register duct opening up and the heater core tubes down. Rotate the plenum up behind the instrument panel and position the plenum to the dash panel. Insert the heater core tubes and mounting studs through their respective holes in the dash panel and the evaporator case.

Install the 3 nuts on the studs along the lower flange and one on the upper flange of the plenum. Install the 3 nuts below the windshield wiper motor to attach the left end of the plenum to the dash panel and the one nut to retain the upper left corner of the evaporator case to the dash panel.

Position the floor air distribution duct on the plenum. Install the 2 screws and plastic push fastener. If removed, position the panel door vacuum motor to the mounting bracket and install the 2 attaching screws.

Connect the white vacuum hose to the outside-recirculating door vacuum motor. Connect the vacuum jumper harness to the plenum harness at the multiple vacuum connector near the floor air distribution duct. Install the floor duct.

If equipped with manual air conditioning, connect the temperature control cable housing to the bracket on top of the plenum and connect the temperature control cable to the temperature blend door crank arm. Adjust the temperature cable.

If equipped with ATC, proceed as follows:

Connect the temperature control cable to the ATC sensor and adjust the cable. Route and connect the vacuum harness connector to the ATC sensor and connect the electrical connector to the ATC servo connector. Do not block the sensor aspirator exhaust port with the excess vacuum harness. Install the ATC sensor tube between the sensor and the evaporator connector.

On 1990-00vehicles:
1. Connect the ATC sensor tube to the evaporator case connector.
2. Install the cross body brace and connect the wiring harness to the blend door actuator.
3. Install the bolt to attach the lower right end of the instrument panel to the side cowl. Install the right side cowl trim panel and tighten the right door sill plate attaching screws.

On 1988-1989 vehicles install the instrument panel pad and the glove compartment door.

On 1990-99 vehicles, push the instrument panel back into position and install all instrument panel mounting screws. Install the right and left lower instrument panel insulators.