Title Page Prey Page Next Page TOC Submit PCR GULFSTREAM IV MAINTENANCE MANUAL AIR CONDITIONING AND PRESSURIZATION SYSTEM - SYSTEM DESCRIPTION 1. General A. Description The environmental control system provides for pressurization, heating, cooling, ventilation and the means for reduction of humidity in flight or on the ground. True air conditioning is classified as heating or cooling as necessary to maintain a specific level of temperature within the occupied areas of the aircraft, regardless of the ambient temperatures or the operating conditions. Pressurization is the control over the pressure within the occupied areas. Supplemental cooling air to the left radio rack, right radio rack, nose compartment, cockpit pedestal, Cathode Ray Tube (CRT) display No. 1 and CRT display No. 2 is provided by mounted fans. The cooling fans help to prevent avionics and electronics equipment from overheating and malfunctioning by circulating air over and around equipment. The air conditioning system is a 3-wheel, air bearing, Air Cycle Machine (ACM), packaged refrigeration unit, which controls the cabin and cockpit temperature by means of mixing hot compressed air and refrigerated compressed air. The dual pack concept provides redundancy in case one unit fails. By air cycle, it is meant that cooling is provided by means of a thermodynamic cycle using only air as the medium (as opposed to vapor cycle systems which employ Freon or other similar gases). The system also employs water separation for humidity reduction. The pressurization system consists of electronic sensing and regulating devices which control the amount of air leaving the aircraft. A pneumatic safety valve is also incorporated, which will automatically regulate the maximum pressure in the aircraft should the automatic electronic control system fail to function properly. If required, the safety valve will limit the maximum pressure buildup within the pressurized areas (safety pressure reli