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Heater core replacement

Good Morning

I have a 91 Mark VII and the heater core can’t be saved any more. I have used cooling system sealant once all ready. I need stsp by step instructions for getting the dirty buggar out. My dash is almost completely stripped out, I can’t get it loose enough to expose the cover on the plenum box. I thought I was smart to use my Dremmel tool to modify the plenum box so I could gain access that way. I was completely successful in exposing the AC Condensor. Please help,

Witts End

I would have purchased a service manual before starting this project. It would have the step-by-step instructions necessary to remove and replace the heater core.

The AC condensor is in front of the radiator. The AC evaporator is what you found.

Here is the procedure from ALLDATA, sorry but it isn’t very specific. You do have to remove the entire heater assembly to gain access to the core.

Disable airbag system as described under MAINTENANCE PROCEDURES/AIRBAG SYSTEM DISARMING.
Remove instrument panel.
Discharge refrigerant from A/C system, then disconnect high and low pressure hoses. Cap hose ends to prevent entry of dirt and moisture.
Drain coolant and disconnect hoses from heater core. Plug hoses and core to prevent spillage.
Remove air inlet duct/blower housing assembly support brace to cowl top panel retaining screw.
Disconnect A/C wiring, if necessary, then working from engine compartment, remove the two evaporator case to dash panel retaining nuts.
Working from passenger compartment, remove evaporator case support bracket to cowl panel attaching screw.
Carefully pull evaporator case away from dash panel and remove from vehicle.
Remove heater core access cover to evaporator case attaching screws.
Remove heater core and seals from case, then remove seals from heater core tubes.
Reverse procedure to install. Rearm airbag as described under MAINTENANCE PROCEDURES/AIRBAG SYSTEM DISARMING.

Do yourself a favor and go to Lincolnsonline.com or a Mark board. It is very likely that someone has generously documented, with pictures, what you need to do.