A method and apparatus for controlling a multiple compressor heat pump system such that when the system is in the heating mode of operation the compressors are cycled individually depending upon the ambient temperature level and are individually co-ordinately operated in a defrost mode. The electrical control means disclosed provides for a second compressor being energized when the outdoor heat exchanger of a first compressor is being defrosted and the first and second contact means located within the individual defrost circuits for the first and second outdoor heat exchangers such that when the first outdoor heat exchanger is being defrosted the second outdoor heat exchanger may not commence a defrost cycle and when the second compressor is being operated in a defrost cycle a first compressor may not commence a defrost cycle.