How do you replace heater core in 1985 Chevy van?

To replace the heater core in a 1985 Chevy van, start by disconnecting the battery and draining the coolant from the radiator. Remove the dashboard and the heater assembly cover to access the heater core. Disconnect the hoses and any attached components, then remove the old heater core and install the new one. Reassemble everything, refill the coolant, and check for leaks before reconnecting the battery.