The air conditioning system should be emptied at an automotive air conditioning facility or a dealership service department. The second step is to take out the heater and the air conditioner housing and put it down on a clean working surface. Go ahead to lift off the evaporator core fasteners, divide the housing and remove the evaporator core out of the housing carefully. The reinstatement is in the opposite sequence of the removal process, with due careful attention being paid to reactive insulating or sealing materials being placed in place around the evaporator core pipes, and around the core itself. Each time the air conditioning system is reinstalled, new O-rings must be employed on the fittings. Should you replace the evaporator core with a new one, then add new refrigerant oil to the new part, however, always remember that it has to match up with the type of refrigerant, R-134a or R1234yf, which might be used in the vehicle. Lastly, the shop where the initial discharge was done must evacuate the system, recharge, and leak test the system.