Air entering a system contains moisture. Moisture in the refrigerant can create oil sludge, which reduces the lubrication properties of the oil and plugs oil passages and screens in the compressor. Moisture can also freeze at the expansion device.
Acid is not introduced into a system; it is formed inside an operating system by the reaction of moisture with the refrigerant. Under the heat of compression, moisture will react with the refrigerant to form hydrochloric and hydrofluoric acid. These acids erode machined surfaces and can cause copper from the system to be deposited on the heated bearing surfaces in the compressor, resulting in compressor failure. Acid also creates sludge and varnish, which act to plug compressor oil passages and restrict the strainers in the lubrication system. These contaminants can cause the insulation on the motor windings to break down. Acid is produced in greater quantities in a system that runs hotter than normal.
