When so set, each switch supplies current from the PC wire to energize an unloader magnet valve which allows control air to pass to the unloaders in the air compressor cylinders. Due to passage of air through the feed valves, the main reservoir pressures drop gradually. Movement of the switch breaks the circuit to the unloader magnet valve and causes the compressor to load. When the compressor relay is energized, it picks up and opens contacts which are in the circuit energizing the unloader magnet valve. This interruption de-energizes the unloader magnet valves and causes the other compressors to load.
All compressors then proceed to pump up the main reservoirs in their respective unit.
This will continue until the pressure reaches 140 pounds in the unit whose switch initiated the loading. The movement will de-energize the CC wire and also the compressor relays in all units. All compressors will unload and remain so until the main reservoir pressure again drops to 130 pounds in one unit. Note that, under this system, it is possible, for the main reservoir pressure to rise above 140 pounds in the units other than the one responsible for the loading. From the compressor, the air passes through an oil separator to the aftercooler assembly.