Mazda Training manual - part 271

Air Conditioning Fundamentals

TC070-05-01S

8  – AIR CONDITIONING 
LUBRICANTS 

 

58

OBJECTIVES 
 
 
After completing this section, you will be able to: 
 
• 

Explain the purpose of refrigeration lubrication. 

 
• 

Identify the differences between mineral oil and PAG oil. 

 
• 

Describe the characteristics of refrigeration oil. 

 
• 

Explain why you must add oil to an A/C system when you replace components. 

 
 
 
REFRIGERATION LUBRICATION 
 
Refrigeration oil lubricates the moving parts and seals of an A/C system. The oil flows with 
the refrigerant throughout the system. Refrigeration oil and motor oil are different. Never use 
motor oil in an A/C system. 
 
 
 
Mineral Oil and PAG Oil 
 
The type of refrigeration oil used in an A/C system depends on the type of refrigerant. In fact, 
when engineers develop a refrigerant, they simultaneously develop the lubrication oil used 
with it. 
 
• 

R-12 A/C systems use mineral oil as a lubricant. Different types of compressors in R-12 
systems require different types of mineral oil. 

 
• 

R-134a systems use oil made of polyalkylene glycols, commonly called PAG oil. 

 
• 

PAG oil and mineral oil are completely incompatible. Never mix them. 

 
 
 
Characteristics of Refrigeration Oil 
 
Refrigeration oil — either mineral or PAG — 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. 

Air Conditioning Fundamentals

TC070-05-01S

8  – AIR CONDITIONING 
LUBRICANTS 

 

59

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 

Answers to 
Review 
Exercise 7 

 

1. DOT4BA 

or 

DOT4BW 

2.  R-12 
3.  R-134a 
4.  no 
5.  reclaimed 

6.  frostbite and 

excessive drying 

7.  R-134a 
8.  R-12 

 

Refrigeration oil readily absorbs moisture. If stored improperly, the oil 
becomes unusable. For example, an unsealed container of PAG oil 
becomes saturated with two percent water if left in a humid climate for 
five days. If you use saturated oil in an A/C system, acids will form, 
damaging seals and other components. Always seal refrigerant oil 
properly after use, and never reuse oil removed from an operating A/C 
system. 
 
Some A/C systems use a compressor with carbon seals. In these cases, 
the refrigeration oil may have a dark color. This color is normal. 
 
 
OIL QUANTITY AND COMPONENT REPLACEMENT   
 
 
In a new A/C system, the compressor holds all the refrigerant oil. The 
compressor mixes the oil with the refrigerant and circulates it 
throughout the system. After the system has been used, some 
refrigerant oil may be stored in the evaporator or condenser. 
 
When you replace an A/C component, you must also replace the 
refrigeration oil trapped in the component. Service manuals contain 
charts describing how much oil to add for various component 
replacements. For example, the chart may tell you to add 30 ml of 
refrigerant oil after replacing a condenser. 
 
If an A/C system develops a leak, refrigeration oil will appear at the site 
of the leak. Any leaking refrigerant evaporates immediately. The 
amount of oil lost depends on the size of the leak and the length of time 
it was leaking. After you repair a leak, replace the amount of lost oil. 
Carefully measure the oil removed during evacuation and replace it with 
a slightly greater amount. 
 

Air Conditioning Fundamentals

TC070-05-01S

8  – AIR CONDITIONING 
LUBRICANTS 

 

60

REVIEW EXERCISE 8 
 
 
Mark each statement as true or false. Check your answers with the answer key on page 62. 
 
1.      True or false? When you replace an A/C component, you will usually need to add 

refrigeration oil as well. 

 
2.      True or false? Refrigerant is usually visible around the area where an A/C system is 

leaking. 

 
3.      True or false? You can reuse refrigeration oil removed from an operating A/C system. 
 
4.      True or false? PAG oil is suitable for R-134a A/C systems. 
 
5.      True or false? Refrigeration oil flows through a special set of grooves and channels 

drilled into A/C system components. 

 
6.   True or false? If refrigeration oil is not sealed properly, it will absorb moisture from the 

air. 

 
7.      True or false? You may use either mineral oil or PAG oil in R-12 systems. 
 

Air Conditioning Fundamentals

TC070-05-01S

8  – AIR CONDITIONING 
LUBRICANTS 

 

61

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 

Answers to 

Review 
Exercise 8 

 

1.  True 

2.  False; oil is 

visible; 
refrigerant 
evaporates 

3.  False

 

4.  True

 

5.  False, oil flows 

with the refrig- 
erant

 

6.  True

 

7.   False, use 

only mineral 
oil in R-12 
systems