In order for a refree circulated to function properly, the proper quantity of refrigerant must be circulated through the system at the proper pressures. Metering devices restrict the flow of refrigerant to create the proper pressure drop between the high side and low side of the system. Metering devices may be or fros of fixed size that provide a continuous restriction in the flow of refrigerant, or they may be valves, which can vary the flow to meet the demands of varying loads.

Metering Device Basics

Mechanical refrigeration and air conditioning systems depend on a change of pres- sure as liquid refrigerant flows into the evaporator. Many different types of mechan- ical and electromechanical devices can be used to create this pressure difference in a system. These devices are referred to as metering devices and are installed between the liquid line and the evaporator. A metering device provides a small opening, or orifice, through which only a certain amount of refrigerant can flow at one time. As the system operates, a limited amount of the refrigerant is allowed to pass through the metering device into the evaporator. Since only a small amount of refrigerant is entering the evaporator, the refrigerant has room to expand and is at a low pressure. However, since only a small amount of refrigerant passes through the metering device, the refrigerant in the liq- uid line remains under high pressure. The metering device must allow just the right amount of refrigerant to pass to sustain this pressure difference.

Types of Metering Devices *
There are many different types of metering devices. The simplest type of meter- ing device is the capillary tube. One of the more complex controls is the electronic expansion valve, which is controlled by a microprocessor. The most common types of metering devices are: • Capillary tube (cap tube). • Metering orifice. • Thermostatic expansion valve (TXV). • Automatic expansion valve (AXV). • Electronic expansion valve (EEV). • Low-side float (LSF). • High-side float (HSF).