Your customers may use one of the following terms to describe the HVAC system they are working on. These terms may refer to either the systems components, or compressor controls, or even the type of refrigerant used in the system. The following is a brief explanation of these terms.
Expansion Valve or Orifice Tube Systems
There are two types of refrigerant flow control valves that are used to describe AC systems. (1) A Thermostatic Expansion Valve (TXV) system uses a valve that modulates the flow of refrigerant into the evaporator based upon the temperature of the refrigerant exiting the evaporator. (2) A fixed orifice tube system uses a predetermined restriction to control the flow of refrigerant into the evaporator. We will describe the variations and operation of these control valves in the Component Topic of this module.
Cycling Clutch or Variable Displacement Systems
These terms actually describe the method the AC system is using to maintain optimum evaporator temperatures. Cycling clutch systems use a thermal or pressure switch to cycle the compressor clutch on and off base upon the temperature of the evaporator. Variable displacement designs use a unique compressor that can vary the stroke of the compressor pistons in response to changes in the evaporator outlet pressure. By varying the displacement of the compressor you vary the flow of refrigerant in the system thereby maintaining optimum evaporator temperatures.
Receiver Filter Drier or Accumulator Systems
These terms describe how the refrigerant is filtered and stored in the system. The receiver filter drier is placed at the outlet of the condenser. These driers are generally used with thermal expansion valves. Accumulators are placed on the outlet side of the evaporator and are generally used in fixed orifice tube systems.