How to Change the Heater Core on a 1999 Chevrolet Blazer

The heater core in a 1999 Chevrolet Blazer is located in the dashboard and is designed to provide the cab of the vehicle with warm air. The heater core takes air that was warmed by the Blazer's coolant system and directs it through the dash vents. Over time, the heater core will get filled with debris. This can cause leaks or outright failure, so replacing the heater core as soon as it begins to show signs of malfunctioning is a good idea.

Things You'll Need

• Socket wrench
• Screwdrivers
• Drain pan
• Coolant
• Water

Instructions

1. Park the Blazer on a level surface and set the parking brake. Open the hood and disconnect the negative battery cable.

2. Turn the two screws on the bottom of the dash panel counterclockwise. Remove the bolt on the dash hear the instrument cluster with a socket wrench. Pull out on the dash panel to remove it. Unplug the electrical connections on the back of the panel and set the panel to the side.

3. Detach the radio from its mounting harness by removing the four bolts holding it in place with a socket wrench. Unplug the electrical connectors in the back, then slide the radio forward to remove it.

4. Remove the six bolts holding the dashboard in place. The bolts can be found between the windshield and the firewall of the Blazer. Pull forward on the dash to make the hiring harness accessible. Unplug the wiring harness, then remove the dash.

5. Remove the radiator cap to release pressure on the coolant system. Place the drip pan underneath the bottom radiator plug. Remove the bottom radiator plug and allow the coolant to drain into the pan.

6. Loosen the hose clamps on the heater core in the upper left of the engine bay. Unscrew the hose clamps with a screwdriver until they slip off the hoses, then disconnect the hoses.

7. Remove the two bolts holding the heater core to the mount with a socket wrench. Pull the heater core towards the windshield to remove it completely.

8. Place the new heater core in the mount and tighten the bolts with a socket wrench. Reassemble everything in reverse order.

9. Replace the radiator plug and tighten it down by hand. Fill the radiator with a mixture of half coolant and half water. Reattach the negative battery cable. Start the Blazer and let it run for a few minutes with the heater on high. Check for leaks. Fill the radiator again, put the radiator cap back on and close the hood.

References

• "Chilton's Chevrolet Blazer/Jimmy/Bravada, 1982-91 Repair Manual (Chilton's Total Car Care Repair Manual)"; Richard T. Smith; 1991