Heat pump reversing valve: refrigerant flow in cooling and heating

The reversing valve's single port always takes hot discharge gas from the compressor, and the center port on the other side always returns cool suction gas to the compressor. In cooling the slide sends discharge gas to the outdoor coil and connects the indoor coil to suction. In heating it sends discharge gas to the indoor coil and connects the outdoor coil to suction, so the two coil lines swap temperature when the mode changes.

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