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The development of acids in the refrigerant of vapor compression refrigerators, heat pumps, and air conditioners can severely shorten the life of the compressor and the refrigerant. Contractors can take steps to prevent this.
The acids sometimes found in refrigerants can be formed by chemical reactions with components and/or materials of construction, lubricating oils, and/or impurities.
The instability of the refrigerant, and thus the formation of acids, is accelerated by elevated temperatures which could be the result of improper operation, such as a failed condenser fan or clogged airflow path.
Checking the system for acid should be a routine maintenance practice, because acid can be easily treated before the compre or fails.
You can check the refrigerant oil for acid, or you can check the refrigerant for the acid. Since a typical hermetic compressor does not have an oil drain, testing the refrigerant vapor is the only practical method on many residential or light commercial a/c units. The advantage to testing the refrigerant for acid is that it is accurate, fast, and inexpensive.
If you decide to use an oil acid test kit, be aware that using the wrong type of test kit with an ester-based (POE) oil can result in a false acid reading, because the oil behaves like an acid to the test kit (that is, the ester oil displays amphoteric properties). That's why many oil acid test kits have one kit (or one scale) for mineral oils and a different test kit (or scale) for POE oils.
A discussion of the different types of acids present in the system is necessary to fully understand the acid-removal process.
UNDERSTANDING ACID
Depending on the refrigerant and lubricant being used, a refrigeration system can contain two types of acids: organic acids (such as oleic acid) and inorganic (mineral) acids (such as hydrochloric acid).
Organic acids are soluble in the oil, do not vaporize, and therefore stay predominately in the liquid oil in the compressor oil sump.
Inorganic acids are only slightly soluble in the oil and are volatile; thus, they can exist both in the oil and can circulate with refrigerant throughout the system. Inorganic acids are much more damaging to the system (they are much stronger and reactive acids) and are the...