Is it normal to have to add refrigerant to a system?

No, refrigerant is not consumed like gas in a car. It also does not lose its ability to be effective. As long as the system does not have a leak, you should not have to add any refrigerant. If a refrigerant leak does exist, we can usually electronically locate it with special sensing equipment. The EPA requires systems that have refrigerant leaks to be repaired or replaced due to the negative effects the refrigerant has on the Earth's atmosphere. Furthermore, if your system gets too low on refrigerant it may freeze up and create water damage. Additionally, you may damage your compressor.