If you are having trouble getting the heater to work in your 1999 Grand Am and you know that the thermostat is good, then you may have a clogged heater core. Another problem that may be the cause is a leaking heater core. This is usually evident when the floor of the vehicle is wet. In any case, when the heater core develops problems, you need to replace it as soon as possible before the problem causes more damage, such as a blown head gasket.
Drain the antifreeze from the coolant system into the drain pan by opening the valve on the bottom of the radiator with a wrench. If you keep the coolant clean, you can reuse it after completing the repair. Place wheel chocks behind the rear wheels. Lift the Grand Am with an automobile jack. Place a jack stand under the car and raise it to the frame.
Crawl under the Pontiac and locate the heater hoses on the back firewall. Remove the drain tube from the heater housing by loosening the clamp with a screwdriver. Disconnect the heater hoses by loosening the hose clamps with the screwdriver. Remove the jack stand from under the Grand Am and lower the vehicle to the ground with the jack.
Loosen the screws on the steering column cover with a screwdriver then remove it. Remove the sound insulators from each side of the car in the dashboard area. Disconnect the air duct from the unit with a screwdriver. Remove the screws from the rear floor outlet with the screwdriver.
Remove the heater core cover by loosening its screws with the screwdriver. Disconnect the heater core clamps from the housing with a wrench. Remove the heater core mounting bolts with the wrench. Pull the heater core into the passenger compartment.
Insert the new heater core in place under the dash console. Tighten the mounting bolts with the wrench. Connect the clamps that attach the heater core to the housing and tighten them with the wrench. Replace the heater core cover on the Grand Am and tighten the screws with the screwdriver.
Connect the rear floor outlet to the heater unit and tighten the screws with the screwdriver. Connect the air duct to the heater unit with the screwdriver. Install the sound insulators on each side. Attach the steering column cover and tighten the screws with the screwdriver.
Raise the Grand Am with the automobile jack. Place the jack stand under the vehicle and raise it to the frame. Crawl under the Pontiac and connect the heater hoses. Tighten the clamps with the screwdriver. Connect the drain tube to the heater housing and tighten the clamp with the screwdriver. Remove the jack stand from under the vehicle and lower the Grand Am to the ground with the jack.
Refill the radiator and reservoir with coolant. Start the vehicle and check for leaks around the hoses and inside the car.
