The Mercury Villager's heater core is within the rear heater/air conditioning assembly. You must remove this assembly to replace the core. The larger task is getting to the assembly, which is located under the left rear quarter trim panel. The entire process can be challenging.
Unplug the negative cable on the Mercury Villager's battery. Drain the cooling and air conditioning systems, using clean containers, if you plan to reuse the coolant. To do this, take off the radiator cap, jack up the van and place your container underneath the radiator below the drain plug, which is usually on the rear bottom. Open the plug, drain all the fluid, replace the plug and lower the van.
Disconnect the heater hoses at the bulkhead and the plug. Remove the center seats and seat belt lower anchor bolts on the left side.
Detach the left rear quarter trim panel from the vehicle. Lift the gate scuff plate from the panel and pry the rear seat remote control from it. Remove the rear radio control panel and climate control panel wiring and pass the lap belt through the panel.
Take off the upper duct from the assembly. Remove the blower motor and resistor wiring, and then the temperature blend and vent door actuator connectors.
Raise the vehicle on jack stands again. Disconnect and plug from the refrigerant line from underneath with the spring lock coupling tool, then lower the vehicle. Remember, if your Mercury Villager uses R-12 air conditioning refrigerant, then only an EPA-certified technician can work on the system.
Remove the heater/air conditioning assembly from the vehicle and the heater core from the assembly.
Install the new heater core into the H/AC assembly and put the assembly into the Mercury Villager.
Connect the refrigerant lines back on the evaporator. You must raise the vehicle again to do this. Use new o-rings with the lines.
Lower the van and reinstall and connect all the wiring connectors, the upper air duct, trim panel, climate control panel, radio control panel and all other components.
Fill the cooling and air conditioning systems. Using new coolant may work best, if you have any doubt that the old coolant is still usable. Refill the air conditioning refrigerant, if you're allowed to do so. Reconnect the negative battery cable.
Run the Mercury Villager's engine until it reaches its normal operating temperature. Observe the climate control operation and check for leaks in the system.
