How do I replace heater core in my 99 3500 chevy exspress van

1. Drain the engine coolant. Refer to Draining and Filling Cooling System in Engine Cooling. 2. Recover the refrigerant. 3. Remove the coolant recovery reservoir or the surge tank. 4. Remove the battery from the vehicle. 5. Remove the A/C accumulator. 6. Disconnect the heater hoses from the heater core. 7. Remove the right kick panel. 8. Remove the right knee bolster. 9. Remove the outer floor air outlet duct. 10. Remove the retaining screws from the heater case. 11. CAREFULLY open the heater core access door in order to obtain the retainers. 12. Remove the retainers from the heater core. 13. Remove the heater core from the vehicle. INSTALLATION PROCEDURE 1. Install the heater core to the vehicle. 2. Install the retainers to the heater core. 3. CAREFULLY close the heater core access door. 4. Install the retaining screws into the heater case. 5. Install the outer floor air outlet duct. 6. Install the right knee bolster. 7. Install the right kick panel. 8. Connect the heater hoses to the heater core. 9. Install the A/C accumulator. 10. Install the battery into the vehicle. 11. Install the coolant recovery reservoir or the surge tank. 12. Charge the A/C system, if equipped with A/C. Refer to Refrigerant Recovery and Recharging in HVAC Systems with A/C-Manual. 13. Fill the engine coolant. Refer to Draining and Filling Cooling System in Engine Cooling.