a method for controlling operation of a system for controlling the atmosphere within a confined space . the system has an electrical control having a display and electrically controlled components . the components include an air compressor , a filter , an air heater , a separator for dividing air into streams of oxygen and nitrogen , and flow control valves for varying the purity of the nitrogen stream . the system also includes sensors for indicating the temperature leaving the heater and the temperature within the confined space . a sensor indicates the pressure upstream of the control valves . an oxygen sensor and a carbon dioxide sensor are included . the method includes the steps of energizing the system and simultaneously operating the electrical control to perform the steps of : operating the compressor to an on or off position responsive to inputs from the oxygen sensor and the carbon dioxide sensor ; operating the flow control to achieve setpoint oxygen and carbon dioxide levels in the atmosphere , in response to inputs from the oxygen sensor and the carbon dioxide sensor ; operating the air heater to maintain a preset value ; monitoring the oxygen sensor , and , compensating the output when a predetermined temperature of the atmosphere is indicated ; monitoring the carbon dioxide sensor , and compensating the output when a predetermined change in the temperature of the carbon dioxide sensor occurs ; and monitoring system components , and , indicating on the display when unsafe or out of range conditions occur .