A water thermostat is used to control the temperature (ideally 65-70 degrees fahrenheit) for the developing solutions. A mercury regulator controls the electrical heating and cooling of the water in the tank in response to the room’s temperature. Typically a Carrier Centrifugal Refrigeration Unit is responsible for cooling the water supplied to the spray chambers and tanks for the developing solutions. It can cool an impressive 100 gallons of developing solution per minute.