Regardless of the type, all air conditioning systems function according to a basic law of physics that states ‘a fluid absorbs heat as it changes from a liquid to a gas, and a vapor releases heat as it changes from a gas to a liquid.’ In an A/C system, refrigerant is the transfer medium used to absorb the heat inside the passenger compartment and release it to the outside air. Refrigerant is a tasteless, odorless gas with an ability to change state rapidly within a specific temperature range. It is also oil soluble and non-corrosive. While there are scores of refrigerants on the market, there are only two types approved by vehicle manufacturers: R-12 and R-134a.

R-12, commonly referred to as Freon, has long been used as the refrigerant in all automotive A/C systems. However, R-12 contains chlorine, which is the primary cause of ozone layer damage. Consequently, legislation was passed calling for a halt in R-12 production by 1996. Long before the phase-out of R-12 began however, the automotive industry conducted extensive research and development to find an environmentally friendly alternative. They ultimately selected R-134a as the new refrigerant, and began using it in vehicles as early as 1992.

R-134a is similar to R-12, in that it absorbs, transfers, and releases heat efficiently. It is also non-flammable, and mixes well with oil, just like R-12. However, R-134a does have some unique characteristics.

  • R-134a requires a special synthetic lubricant since it does not mix with mineral oil (standard R-12 lubricant).
  • R-134a operates at higher discharge pressures than R-12. Therefore, systems using R-134a may not cool as well as R-12 when the vehicle is idling for extended periods (e.g. heavy traffic).
  • R-134a and R-12 cannot be mixed, which is why separate equipment is needed to service vehicles using either refrigerant.

Depending on the vehicle, refrigerant capacity can range anywhere from about 28 ounces (1.75 lbs.) to as much as 64 ounces (4.00 lbs.) or more. To avoid an improper charge, always consult the manufacturer's specifications for refrigerant capacity. An improper charge will cause reduced system performance, and may even result in system damage.

Refrigerant Oil

In order to function properly, an A/C system requires the appropriate type and amount of oil. In addition to lubricating the compressor, refrigerant oil also maintains the operation of the expansion valve on systems so equipped. Since the oil is transported through the system by the refrigerant, it has to be compatible with the type of refrigerant being used. Mineral oil is the lubricant used for all R-12 systems, while R-134a systems use synthetic oils such as PAG (polyalkylene glycol) and POE (polyolester).