If you need to change your heat pump, you would be best served by contacting local qualified and licensed contractors to come out and give you and evaluation and an estimate. Once it is evaluated they can let you know whether or not it needs changed and why.
No we need not change the heat pump. Most of the pump has 4 valves (solenoid) and it change between modes. First valve controls the delivery of refrigerant from a refrigerant heat exchanger. It avoid overpressure at the suction side of the compressor and provides a pressure limiting function.