An improved multi-functional air-conditioning water heater is devised to solve the problem of frequent starts and stops of fan

which always occurs while a traditional one produces hot water in summer. The improved multi-functional air-conditioning water heater can be highly efficient and stable operation in the various modes of different seasons owing to the change of input voltage and speed of fan

and improvement of the outdoor air-cooled heat exchanger. The critical output voltage for the stable operation of compressor and fan is found out

and the relationship between COP and the opening degrees of throttling valve is investigated. Compared with the system improved before

the system's stability has a great enhancement after adding a transformer in the multi-functional air-conditioning water heater. When the outdoor environment temperature is 32 ℃

the opening degree of of throttling valve is 0.4

and the output voltage of transformer is 160 V. The improved system can reach an optimum COP of 4.68 under the hot water only mode in summer.