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Modern Refrigeration and Air Conditioning
and polyalkylene glycol (PAG) lubricants are designed
specifically for the new, alternative refrigerants. There
are numerous grades of polyol ester lubricants. They
are miscible with the most commonly used CFCs,
HCFCs, and HFCs; however, polyol ester lubricants
may not be approved for use in certain compressors.
Figure 6-18 lists the appropriate lubricant for various
refrigerants.
6.7.3 Handling Refrigeration Lubricants
Refrigeration lubricant must be kept in sealed con-
tainers, transferred in chemically cleaned containers
and lines, and not exposed to air where it will absorb
moisture. Refrigeration lubricant comes in one- or five-
gallon cans and in barrels. It is advisable to purchase
lubricant in small sealed containers, holding only
enough for each separate service operation. Unused
lubricant that is allowed to remain in the container or
lubricant transferred from one container to another
may pick up some moisture and dirt. Always seal a
lubricant container after drawing lubricant from it.
6.7.4 Adding Lubricant to a System
Having the correct amount of lubricant in a sys-
tem is very important. Lack of lubricant will shorten
the life of compressors, increase friction, and cause
noise. However, an overcharge of lubricant will cause
the compressor to pump excessive amounts of lubri-
cant, reducing its refrigerant-pumping capacity. It will
also subject the compressor valves to severe strain.
When considering which lubricant to add to a sys-
tem, follow the equipment manufacturer’s recommen-
dations. Make sure the lubricant is compatible with
the refrigerant being used. Also, be sure to follow the
manufacturer’s viscosity, pour point, and floc point
recommendations. On a service call, add lubricant only
if there is a sign of lubricant leakage.
Most hermetic compressors do not have a method
of measuring the amount of oil in a system, but it is
rarely necessary to add lubricant to a hermetic sys-
tem. However, leaking refrigerant always carries some
lubricant with it. This lost lubricant should be replaced.
If the hermetic unit is equipped with service valves,
lubricant can be siphoned or poured in.
If a system has a low-side leak, moisture and air
may have entered. In this case, it is best to replace the
refrigeration lubricant. Measure the amount of lubri-
cant removed and replace it with the same amount
of clean, dry lubricant. Some compressors have an oil
reservoir and sight glass that allows a technician to
add new refrigerant oil by sight. The unit should be
charged in much the same way as when adding refrig-
erant to the system.
A pump may also be used to put lubricant into a
system. The charging lines must be purged to remove
air, moisture, and dirt. A hand pump can build up
pressures as high as 300 psig (2200 kPa), which allows
lubricant to be forced into the system even when the
system is under pressure. Adding lubricant using
a hand pump is covered in Chapter 53, Servicing
Commercial Systems.
6.7.5 Contaminated Lubricant
Lubricant that is removed from a system should
be translucent. Discoloration means that it is impure.
Compatible Refrigerants and Lubricants
Refrigerant Appropriate Lubricant*
R-11 AB MO
R-12 AB MO
R-13 AB MO
R-22 AB MO
R-23 POE
R-123 AB MO
R-124 AB MO
R-125 POE
R-134a POE PAG**
R-401A POE AB
R-401B POE AB
R-401C POE AB
R-402A POE AB MO
R-402B POE AB MO
R-403B POE AB MO
R-404A POE
R-407A POE
R-407B POE
R-407C POE
R-410A POE
R-500 AB MO
R-502 AB MO
R-503 AB MO
R-507A POE
R-717 MO
* POE = Polyol ester / AB = Alkylbenzene / MO = Mineral oil / PAG =
Polyalkylene glycol
**PAG is used primarily for automotive applications as a lubricant with R-134a
Goodheart-Willcox Publisher
Figure 6-18. This table shows which lubricants are appropriate
for specific types of refrigerants.