How to Change the Heater Core in a 1990 Chevy S-10 Without Air Conditioning

Changing the heater core in a 1990 Chevy S-10 can be a challenge if the heater core is already leaking in your car. Damage to the heater core typically occurs from a blocked or clogged coolant flow hose. Forgetting to have your coolant system flushed and refilled throughout the year can damage the heater core as well. As with every attempted auto repair, you should always use caution and never forget to wear eye protection.

Instructions

Disconnect the negative battery cable using your socket wrench set. To best identify the proper cable, look for a minus symbol on the top of the battery next to the contact post.

Wrap the metal contact at the end of the cable completely with the black electrical tape.

Lay the cable down carefully while making sure that it does not come in contact with any other metal surfaces under the hood.

Position your drain pan underneath the front of the car. It should be directly under the drain plug on the radiator.

Unscrew the drain plug and take the radiator cap off.

Drain the entire radiator of its liquid coolant. Leave your drain pan in position until you're finished with the heater core repair.

Disconnect the two hoses connected to the heater core while gently using pliers. You can easily access the hoses from under the hood of the car. They are on the passenger side and can be seen protruding out of the vehicle's firewall. This is the back wall of the engine compartment that separates the inside from the outside of the car.

Plug up the hoses and the two holes in the heater core with paper towel to prevent leftover coolant spillage.

Open the front passenger side door and look just below the dash for a rectangular-shaped case. This is the cover that protects the heater core from being kicked or damaged. Remove the five screws from the cover with your Philips screwdriver. Gently remove the case cover and place it out of your work area. Keep the screws with the cover so they don't get lost during the repair.

Remove the two screws at the bottom of the heater core, one on the left and the right bottom of the core. Slowly bend both of the metal straps that are holding the heater core in place outward, or toward you, to create extra space for removing the heater core.

Lay the towel down on the floor area underneath the heater core to catch any drips or spills. Remove the heater core carefully from its position.

Clog up the two coolant holes on the new heater core to prevent debris from getting in the heater core during installation.

Carefully place the new heater core back into the same position the old core was in under the dashboard. Bend the two metal holding straps back into place and secure them with the two screws. Reinstall the heater core case cover and its screws.

Unclog both heater core tubes from inside the engine area. One at a time, also unclog each of the two hoses and reconnect them to the heater core.

Close the drain plug at the bottom of the radiator and refill the radiator with coolant.

Remove the tape from the negative battery cable and reconnect it to the car battery. Start your car and let it run for 15 minutes while rechecking your installation for possible leaks.