Abstract: A method for maintaining a preselected concentration of non-condensible gases in a condenser is disclosed. A compressor supplies the condenser with compressed ammonia. The compressed ammonia includes non-condensible gases. At least a portion of the compressed ammonia condenses, forms condensed ammonia and exits the condenser. A pressure controller operates an automatic valve to vent at least a portion of the non-condensible gases from the condenser. A temperature element senses the condensed ammonia temperature and sends a signal, based upon the condensed ammonia temperature, to the pressure controller. The pressure controller uses the signal to reduce the pressure of the condenser from a predetermined value to a computed value estimated to be necessary to maintain the preselected concentration of non-condensible gases in the condenser.