Total Acid Number is an analytical test to determine the deterioration of hydraulic oils and
lubricants. The more acidic the oil there is, the further its degradation has proceeded. As oils or
hydraulic fluids breakdown, they generally form acidic byproducts that can be corrosive to metal
components, accelerate wear, form deposits and increase viscosity. As a fluid degrades, the levels of
corrosive acids increase, along with the danger of component failure. An increased TAN is a result of
oxidation of the oil, perhaps caused by overheating, overextended oil service, or water and/or air
contamination. Components within refrigeration systems are particularly susceptible to acid attack.
This can occur when air containing water vapor enters the system, or alternatively when the system is
subjected to excessive heat and the refrigerant drier releases retained water. When this happens, acids
created by the reaction of the air, water, refrigerant and oil cause iron components in the system to
become plated with copper, which can cause bearing failure due to copper plating. In refrigerant
systems, the acid content of the oil, the moisture content and the copper concentration level need to be
regularly monitored in order to indicate incipient problems.