The iGS-061 will perform CO2 enrichment during the day only (when light is sensed by the photocell). The enrichment starts when the CO2 concentration falls below the set point minus the differential. (i.e. Set point = 1200 ppm Differential = 150, CO2 enrichment starts below 1050 ppm and stops beyond 1350 ppm). The differential modifies itself until the controller senses no more overshooting or undershooting of user set point. Fixed differential values can also be set for more specific needs. As a safety feature, the high temperature shut off function will inhibit operation while temperature is over the user setting. This interruption is maintained until temperature falls below the user high temp setting. To inhibit this feature, simply set the limit to its highest value. The controller can also be set to vent (extract) CO2. In this case, the high temp shut off feature becomes a low temp shut off limit to prevent excessive cooling conditions.