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The Magma Copper Mine AC system designed by the Carrier Corporation was the first underground mechanical air conditioning system in North America. The initial installation of refrigerated cooling equipment in the Magma Mine at Superior, Arizona was necessary due to the increase in temperature lower into the mine. Below the 2000-foot level, the increase in rock temperature is approximately 1½ degrees F. per 100 feet of depth. The rock temperature on the 2000-foot level is 109°. 

The mechanical refrigerating units, which were installed in the mine during the first half of 1937, were located on the 3600-foot level -- the lowest working level at that time. All equipment had to be lowered through shaft compartments 40 inches by 60 inches in size. For this reason, two units of 140-ton capacity, rather than one larger unit, were selected. This also gave the plant an added flexibility, as one unit could be operated while the other was shut down to have the condenser tubes cleaned. By changing valves, either set of cooling coils could be connected to either refrigeration unit.

The newly installed Cooling unit would cool in mine by an average of 10° on the day of activation and 20° in about a month all of this happening 3600 feet below the surface of the earth. 

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