Refrigerator User Manual

5
5. Recover the CFC charge into a proper
recovery cylinder. Use normal service prac-
tices. If the correct charge size is not known,
weigh the amount of refrigerant recovered.
6. Replace the filter/drier. It is routine practice to
replace the filter/drier following system mainte-
nance. Replacement driers are available that are
compatible with Suva
®
refrigerants. See page 2
of this manual for additional information on
driers.
7. Evacuate system and check for leaks. To
remove air or other noncondensables in the
system, evacuate the system to near full vacuum
(29.9 inHg vacuum [500 microns] or less than
10 kPa).
8. Charge with Suva
®
refrigerant. In general, the
refrigeration system will require less weight of
the Suva
®
134a than of R-12. The optimum
charge will vary depending on the system design
and operating conditions. For most systems the
best charge size will be 75–90% by weight of
the original R-12 charge.
For best results:
• It is recommended that the system be initially
charged with about 75% by weight of the
original charge.
• Add the initial charge of Suva
®
refrigerant
to the high-pressure side of the system
(compressor not running) until the system
and cylinder pressures equalize. Then connect
to the low-pressure side of the system, start
the compressor, and load the remainder of the
refrigerant slowly to the suction side of the
system.
9. Start up system, adjust charge size. Label
system for the refrigerant and lubricant used.
Start the system and let conditions stabilize. If
the system is undercharged, add Suva
®
134a in
small amounts until the system conditions reach
the desired level. See the Pressure/Temperature
Charts in this bulletin to compare pressures and
temperatures.
Suva
®
refrigerants are more sensitive to charge
size than CFCs. System performance will
change quickly if the system is overcharged
or undercharged. Sight glasses in the liquid
line can be used in most cases as a guide, but
system charge should also be determined
by measuring system operating conditions
(discharge and suction pressures, suction line
temperature, compressor motor amps, super-
heat, etc.). Attempting to charge until
the sight glass is clear may result in over-
charging the refrigerant. Please read “How
to Determine Suction Pressure, Superheat and
Subcool” on page 8.
Retrofit of R-502 Systems to
Suva
®
HP62 or Suva
®
507
The following detailed discussion is the recom-
mended procedure for retrofitting R-502 systems
to Suva
®
HP62 or Suva
®
507.
1. Establish baseline performance with CFC.
Collect system performance data while the
R-502 is in the system. Check for correct
refrigerant charge and operating conditions. The
baseline data of temperatures and pressures
at various points in the system (evaporator,
condenser, compressor suction and discharge,
superheat and subcool, etc.) at normal operating
conditions will be useful when optimizing
operation of the system with the Suva
®
refriger-
ant. A System Data Sheet is included at the
back of this document to record baseline data.
2. Drain mineral oil or alkylbenzene from the
system and measure the volume removed.
Leave the CFC refrigerant in the system. If
mineral oil or alkylbenzene is the existing
lubricant, it will have to be drained. This may
require removing the compressor from the
system, particularly with small hermetic com-
pressors that have no oil drain port. In this case,
the lubricant should be drained from the suction
port on the compressor after the R-502 has been
properly recovered. For an effective flush, it is
important to remove at least 50% of the lubri-
cant in all cases. Larger systems may require
drainage from additional points in the system,
particularly low spots around the evaporator. In
systems with an oil separator, any lubricant
present in the separator should also be drained.
In all cases, measure the volume of lubricant
removed from the system. Record this informa-
tion on the Retrofit Checklist (see Appendix).
Compare this volume with the compressor/
system specifications to ensure that the majority
of lubricant has been removed. Consult the
compressor manufacturer for recommendations
on allowable residual MO/AB in POE lubricant.
If poor system performance is noted on start-up,
an additional lubricant change may be required.