Manual for Refrigeration Servicing Technicians - UNEP - Division of ...

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Retrofitting
7 - If the refrigerant to be added to the system is incompatible with
the existing oil (typically a mineral oil) then it must be removed
(otherwise, this stage can be ignored). Drain and recover the
existing mineral oil charge, measure the quantity and compare
with the recommended oil charge to determine the quantity of oil
left in the system. A major problem with retrofits is removing the
residual mineral oil. This is important because enough mineral oil
is not removed, it can deposit on the evaporator heat exchanger
surfaces, severely degrading performance. Since many small
hermetic compressors do not have oil drains, removal of the
compressor from the system may be necessary for draining the
lubricant. The best point in the system to drain the lubricant is
the suction line of the compressor. Small hand-operated pumps
are available which permit insertion of a tube into the compressor
access port for removal of the mineral oil without removing
the compressor from the system. Remember that most of the
mineral oil must be removed from the system before adding the
replacement lubricant.
8 - Replace all equipment components and accessories that will be
affected by the new alternative refrigerant and the refrigerant oil
suitable for the new alternative refrigerant e.g. expansion valve,
gaskets, filter drier, etc., as recommended by the manufacturer.
Most CFC or HCFC systems with expansion valves will operate
satisfactorily, however, it may be necessary to adjust the superheat.
If the system uses a capillary tube, it will need to be replaced with
one of greater or lesser restriction in order to achieve satisfactory
performance over the complete range of design conditions. It is
recommended that the technician consults with the equipment
manufacturer before replacing the capillary tube.
9 - Charge the system with new and correct amount of alternative
refrigerant oil as recommended by compressor/system manufacturer.
10 - Reinstall the compressor following the standard service practices
recommended by the manufacturer. If an oil pump was used to
remove the oil, reseal the access port.
11 - Run the system while performing the oil change procedure as many
times as necessary until the mineral oil in the system does not
exceed the recommended 5% acceptable level. Test kits are
available from several lubricant suppliers that check for residual
mineral oil content. Generally, it will require about three charges to
get the mineral oil content down to the acceptable level.
12 - Leak test the system with oxygen-free dry nitrogen and observe a
24-hour standing pressure. Make corrections if deemed necessary.
13 - Evacuate system to at least 1000 microns (1 mbar, 29.87 in Hg)
using an appropriate vacuum pump and an electronic vacuum
gauge. Use normal service practices to reconnect and evacuate the
system, to remove air and other non-condensable contaminants.
14 - Charge the system with the appropriate amount of alternative
refrigerant. This can normally be approximated by using the ratio
of liquid densities at the condensing temperature. When charging
the system with alternative refrigerant, use the same charging
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