Where is the heater core on a 91 skylark how hard is it to change Car has ac?

Disconnect the negative battery cable. Drain the engine coolant into a clean container for reuse. Raise and safely support the vehicle. Remove the rear lateral transaxle strut mount, if necessary. Remove the drain tube and disconnect the heater hoses from the core tubes, lower the vehicle. Remove the sound insulators, console extensions and/or steering column filler, as required. remove the floor console outlet ductwork and hoses. remove the heater core cover. Remove the heater core mounting clamps and remove the heater core. This information was taken from chiltons auto repair manual. So good luck and hope it works out