Abstract: A semi-conductor wafer polishing head includes three air lines for controlling three respective head functions, and an air control system providing precise head control and functional checking of each head sub-system, including air line pressure checking and chamber leak rate testing. The control system includes electrically operated valves for selectively coupling air chambers in the head with either a source of pressurized air, a source of negative air pressure, or a vent to atmosphere. A pair of air gauges are employed to check chamber leak rate respectively during positive and negative air pressure tests.