A collector for the liquid phase of the working medium of an air conditioning system has first and second connecting pipes provided for connection into the circuit of an air conditioning system. One of the connecting pipes continues in a guide tube which is guided through the interior of the container of the collector. Part of the guide tube runs through the bottom region of the container, which is provided for vertical arrangement, and has at least one opening for recycling collected oil and the liquid phase of the working medium into the working medium circulating through the air conditioning system. In order to separate the liquid phase of the working medium of the air conditioning system, a cyclone-like separating device is provided. The separating device has a cyclone chamber and a central outflow connecting pipe forming an overflow. One of the connecting pipes leads tangentially into the cyclone chamber and the open end of the guide tube ends at a short distance before the outflow connecting pipe. The collector is thereby effective as a separating device for separating off liquid phases owing to the cyclone effect in the cyclone chamber when flow passes from the first connecting pipe to the second connecting pipe while, when the direction of flow is reversed, the collector returns the liquid phase, including oil, present in the collector through the opening into the flow in the circuit.