The invention relates to a control method used when an air conditioner heating mode is started. The control method not only enables an air conditioner to be shut down in time to protect a compressor from being damaged when refrigerant is not sufficient, but also can effectively avoid the situation that when outdoor temperature is low and the refrigerant is sufficient, due to a low voltage switch in a disconnected state, the air conditioner is shut down, and therefore normal operation of the air conditioner is effectively ensured.