An exchanger for a phase changing refrigerant including a horizontal distributor tube, a horizontal collector tube, and at least one refrigerant carrying heat exchanger tube connected therebetween. A refrigerant gas inlet into the at least one heat exchanger tube is arranged in an upper portion of a cross section of the horizontal distributor tube. A refrigerant outlet from the at least one heat exchanger tube is arranged in an upper portion of a cross section of the horizontal collector tube for condenser operation of the multi channel heat exchanger so that oil separation is provided in a lower portion of the cross section of the horizontal distributor tube and liquid refrigerant separation is provided in a lower portion of the cross section of the horizontal collector tube.