Air conditioning system and heat pump unit

The invention discloses an air conditioning system and a heat pump unit. The air conditioning system comprises a compressor, a first heat exchanger, a throttling device and a second heat exchanger, wherein the compressor, the first heat exchanger, the throttling device and the second heat exchanger are sequentially connected through a coolant pipeline. The first heat exchanger comprises multiple heat exchange flow paths. The air conditioning system has the heating circulation mode. In the heating circulation mode, and at least part of a coolant sequentially flows through at least part heat exchange flow paths of the compressor, the second heat exchanger, the throttling device and the first heat exchanger and then flows back into the compressor. According to the setting of the air conditioning system, and asynchronous heat exchanger is conducted between the bottom heat exchange flow path located at the bottommost portion of the multiple heat exchange flow paths and the other heat exchange flow paths in the multiple heat exchange flow paths at least in the heating circulation mode, so that the bottom of the first heat exchanger is prevented from being frozen. According to the air conditioning system and the heat pump unit, the risk that the bottom of the first heat exchanger is frozen can be lowered, and the performance and the reliability of the air conditioning system are improved.