Receiver fill valve and control method

A method for controlling a heat pump selectively operable in a heating mode, a defrost mode, and a transition mode, the heat pump includes an indoor heat exchanger, an outdoor heat exchanger, a compressor compressing a refrigerant, a receiver, a heating expansion valve, a cooling expansion valve, a directional valve, a check valve, and a receiver valve, the directional valve determines a direction of flow through the indoor heat exchanger and the outdoor heat exchanger, the heating expansion valve connects the outdoor heat exchanger in fluid communication with the receiver, the cooling expansion valve connects the indoor heat exchanger in fluid communication with the outdoor heat exchanger, and the check valve and the receiver valve are connected in parallel flow relationship with each other to convey the refrigerant between the indoor heat exchanger and the receiver, the method comprising:

• operating the heat pump in the heating mode by releasing heat from the indoor heat exchanger and absorbing heat into the outdoor heat exchanger;
• after the heating mode, operating the heat pump in the defrost mode by opening the cooling expansion valve and releasing heat from the outdoor heat exchanger;
• and
• transitioning out of the defrost mode and back to the heating mode via a transition mode, wherein said transition mode comprises the steps of
• (a) releasing heat form the outdoor heat exchanger,
• (b) opening the heating expansion valve and closing the receiver valve while the compressor continues running;
• wherein the step of closing the receiver valve prohibits the refrigerant from flowing from the receiver to the indoor heat exchanger and wherein the step of opening the heating expansion valve is performed while the cooling expansion valve is still open;
• and
• wherein said steps of the transitioning mode occur after the defrost mode and prior initiating the heating mode.