How do you change a heater core on an 1989 Chevrolet G20 Van?

To change the heater core on a 1989 Chevrolet G20 Van, first, disconnect the battery and drain the cooling system. Next, remove the dashboard and the heater assembly by detaching any necessary screws and bolts. Once the heater assembly is out, you can access the heater core, which is typically secured with clips or screws; remove these to take out the old core. Install the new heater core in reverse order, reassemble the heater assembly and dashboard, refill the cooling system, and finally reconnect the battery.