A refrigeration compressor is an essential part of what makes refrigeration technology work. A compressor is like a small motor — it consists of a piston, a crankshaft, and a connecting rod that connects the piston to the crankshaft. Similar to the engine in a car, a refrigeration compressor produces compression over its stroke as it is operated.
As the piston moves up and down in the cylinder, it will compress whatever is in the bore of the compressor. This essentially forces anything in the bore of the compressor into a smaller area through the use of the compressor technology. In a refrigerator, this is used to push refrigerant through. A refrigeration compressor is run by electricity, and the compressors have an electric motor component that powers the piston and crankshaft in order to compress the refrigerant being used.
Each refrigeration compressor has a cylinder head at the top of the compressor assembly. There are also valves in the cylinder head of a compressor. One set of valves, called intake valves, allow refrigerant to enter the cylinder, and the other set of valves, known as exhaust valves, allow refrigerant under pressure to leave the cylinder.
In a refrigeration compressor, the values used are reed valves. These are very thin valves that are easily moved by the pressurized refrigerant at the proper time in the cycle. Once the refrigerant is pressurized, it passes through the system, where it expands and cools. This expanding and cooling process occurs because of the laws of thermodynamics, which dictate that as a liquid expands into a vapor, it absorbs heat.
Refrigeration compressors often require a capacitor as part of the electrical system as well. This requirement exists because the compressors need the extra boost of capacitors when they start up. A capacitor is like a small battery that stores an electrical charge and allows the compressor to use some of that charge when it starts up to help it begin to compress the refrigerant and do its work powering the system.
Some refrigerators have independent compressors for the refrigerator component and the freezer component. These are widely thought to be more efficient, but dual compressor refrigerators are generally more costly than those with a single compressor. In any case, compressors do not run constantly, but instead automatically turn on intermittently when necessary to ensure the appropriate air temperature inside the refrigerator.