If you notice the floor of your 1992 Toyota pickup is wet but cannot determine the source of the water, you likely have a leak in the heater core and must replace it. You may also have a heater core problem no heat is entering the cab of the truck when you know the thermostat is good and you have plenty of coolant in the engine. This project can become a bit involved; set aside a full day to complete it to avoid the need to rush.
Pop the hood on the Toyota pickup, and disconnect the negative battery cable by loosening the terminal nut with a wrench. If your truck has an air conditioner (AC) installed, discharge the AC system properly using an approved fluorocarbon recovery kit. Do not discharge the gas into the air.
Drain the coolant into a drain pan by opening the valve on the bottom of the radiator using a wrench. Put the drain pan up and out of reach of children and animals. Label the hoses to the heater noting their correct locations with a marker and masking tape. Disconnect the hoses using a screwdriver to loosen the hose clamps.
Remove the instrument panel inside the cab of the truck, using a wrench to loosen the bolts. Look for most of the bolts around the bottom perimeter of the dash panel. You may find several in the glove box as well.
Disconnect the ductwork from the heater unit. (You may need a screwdriver to assist in disassembling the ductwork.) Unhook the springs connecting the control cables to the heater unit. Take care not to kink or otherwise damage the control cables. Unplug the wiring harness from the heater blower.
Remove the four bolts mounting the heating and cooling unit to the firewall using a wrench. Pull the unit away from the firewall into the passenger compartment of the truck. Despite the fact that you have drained the cooling system, a significant amount of fluid will remain inside it. Clean the area with old towels.
Remove the bolts holding the heater core to the unit using a wrench. Slide the heater core up and away from the heater unit.
Slide the new heater core into place on the unit, and tighten the fasteners with a wrench. Push the heater unit into place on the firewall, and install the mounting bolts. Tighten the bolts with a wrench.
Connect the control cables to the heater unit, hooking the springs into place. Take care not to kink or damage the control cables. Connect the ductwork to the heater, snapping it into place.
Install the instrument panel, and tighten the retaining bolts with a wrench. Connect the heater hoses to the heater core in the engine compartment, and tighten the hose clamps with a screwdriver. Refill the radiator and reservoir with engine coolant.
Recharge the air conditioner with approved fluorocarbons if you have an AC unit. Connect the negative battery cable, and tighten the terminal nut with a wrench.
Start the Toyota, and allow it to reach operating temperature. Check the system thoroughly for leaks in the engine compartment as well as inside the truck cab.
