大客车空调设计（部件）英文.ppt

* RECEIVER-DEHYDRATOR The receiver-dehydrator, often called accumulator-drier, filter-drier, etc., is a metal tank that collects liquefied refrigerant as it leaves the condenser. It strains the refrigerant and removes moisture by means of a special desiccant (drying agent). The receiver may also contain a safety valve. In the event of fire or other overheating, the valve will release the refrigerant charge when pressure in the system exceeds around 500 psi (3 448 kPa), depending on the system. Fig. 22- 7. From the receiver-dehydrator, the high pressure liquid refrigerant is piped to the expansion valve. A SIGHT GLASS is located in the line or in the top of receiver-dehydrator. SIGHT GLASS A sight glass serves two functions. It provides a visual means of making an inspection of the refrigerant as it moves to the expansion valve. The presence of bubbles or foam (at temperature above 70°F or 21°C), may indicate the system is low on refrigerant and must be charged (filled). Fig. 22-5. Some sight glasses also indicate the presence of moisture in the refrigerant. If excess moisture is present, a moisture sensitive element turns pink. If moisture content is within limits, the element remains blue. EXPANSION VALVE The Refrigerant-12 arriving at the expansion valve is in a liquid state and is under heavy pressure (100 to 250 psi or 689 to 1 724 kPa). The expansion valve serves two functions. It meters refrigerant into the evaporator coils, and also reduces the pressure. It must administer the correct amount of refrigerant for all conditions, neither too much nor too little. A typical expansion valve is shown in Fig. 22-8. Study its parts. Notice that refrigerant from the receiver enters through a fine screen in the high pressure liquid inlet. Further movement of the refrigerant is controlled by the spring-loaded valve. The action of this valve is controlled by three forces: 1. Valve spring tends to close valve opening. 2. Suction manifold