You can use either R12 or R134a in the system. Use the correct connections supplied in the kit, depending on what refrigerant youll be using. A trained technician should check and fill the system so it can be properly evacuated and checked for leaks. Also, the technician should put in the correct amount of oil and refrigerant, or the system will not operate properly. Excessive refrigerant can hinder the cooling capacity of the system.