System Oil

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Lubricant

Refrigeration oil lubricates the moving parts and seals of an A/C system.The oil flows with the refrigerant throughout the system.

Mineral and PAG oil

The type of refrigeration oil used in an A/C system depends on the type of refrigerant. When engineers develop a refrigerant, they simultaneously develop the lubrication oil to use with it. R12 A/C systems use mineral oil as a lubricant. R134a systems use oil made of polyalkylene glycols, commonly called PAG oil. PAG oil and mineral oil are completely incompatible and should never be mixed. Refrigeration oil, is highly refined and free of the additives and detergents found in conventional motor oil. Refrigeration oil flows freely at temperatures well below freezing, and it includes an additive to prevent foaming in the A/C system. Refrigeration oil readily absorbs moisture. If stored improperly, the oil becomes unusable. If you use saturated oil in an A/C system, acids form, damaging seals and other components. Always seal refrigerant oil properly after use, and never reuse oil removed from an operating A/C system.

In an A/C system, the components hold the refrigerant oil.The compressor helps to mix the oil with the refrigerant and circulates it throughout the system. Both oils are available in different viscosities. Always ensure the correct oil type and viscosity is placed into an A/C system. 

Polyol ester oil

Polyol Ester (POE) has good miscibility with HFCs. It is an alcohol-based oil. Its ability to change viscosity with a change in temperature makes it an attractive alternative to PAG oil although some controversy exists which states the POE breaks down into alcohol and acid if in contact with moisture. It is compatible with R12, R134a and CO2-based A/C systems. POE is not an OEM oil and should only be used if specified by the A/C manufacturer. Aftermarket retrofitting is generally associated with the use of POE.

Oil viscosity

The higher the viscosity number the greater the viscosity and the higher its resistance to flow. This means the liquid is thicker.

The following is a list of recommended lubricants for R134a compressor applications:

Behr/Bosch rotary compressors – Ester 10  0   Matsushita (all) – Ester 100
Behr/Bosch piston compressors – PAG 46       Mitsubishi FX80 – PAG 100
Calsonic V5 – PAG 150                                    Mitsubishi FX105 –   PAG 46
Calsonic V6 – PAG 46                                      Nihon (all) – Ester 100
Chrysler RV2 – Ester 100                                 Nippondenso 6P, 10P, 10PA, 10P08E –
                                                                           PAG 46
Chrysler C171, A590 & 6C17 – PAG 46          Nippondenso SP127, SP134 & 6E171 –
                                                                           PAG 46
Diesel/Kiki (Zexel) DKS, DKV &                    Nippondenso TV series – PAG 125
DCW – PAG 46
Ford FS6, FX15, FS10, 10P &                          Panasonic (all) – PAG 46
10PA – PAG 46

When replacing an A/C component, the oil trapped in the component that is being replaced ust also be replaced. Service manuals contain charts describing how much oil to add for various component replacements. Charts that refer to replacing the quantity drain should be gnored.The correct amount of oil must be replaced if the system is to function correctly. If the ystem has a severe oil shortage then replacing the quantity drained will not help the system peration and will not stop the system from eventual failure.This can cause a great deal of customer dissatisfaction and responsibility may be aimed at the last technician who worked onthe system.This is another reason why it is important as a technician to record all work carried ut on a vehicle’s system especially A/C related. Oil removed and oil added must be carefullyrecorded including refrigerant and components.

Oil stains

An oil stain on a connection or joint indicates that refrigerant is leaking from that place. This s because the compressor oil mixed in with the refrigerant escapes with the refrigerant when efrigerant gas leaks out from the refrigeration circuit, causing an oil stain to form at the place here the refrigerant gas is leaking out.

If such an oil stain is found, parts should be retightened or replaced as necessary to stop the as leakage. Gasketed compressor joints and pipe connections are the places where oil stains re most likely to be found, and the condenser, due to its position, is prone to leaks so it is mportant to check all these places. R12 mineral oil leaves a clear oil stain but R134a PAG oil vaporates so this test will not be visual without the aid of a UV lamp.The UV lamp will highlight tracer fluid inside the system. Most manufacturers now place tracer dye inside the system rom manufacture.The amount of oil lost depends on the size of the leak and the length of time t was leaking.After you repair a leak, replace the amount of lost oil. Carefully measure the oil emoved during evacuation and replace it.

Note – overfilling the system with refrigerant oil reduces the cooling effect. Follow the nstructions provided by the manufacturer of the servicing unit when topping up the efrigerant oil. When topping up the refrigerant oil, make sure that the filling equipment hose, container) is clean and dry.The oil container must be sealed immediately after use. 

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