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

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Retrofitting
5 - Evaluate thermostatic expansion valves (TXVs) and new refrigerant
for proper capacity and superheat. Replace the whole valve or
power head if necessary. Existing R22 valves may be under-sized
for higher mass flow refrigerants R507A, R404A and R422A.
6 - Replace O-rings on the receiver float, and receiver optic switch.
7 - Replace nylon gasket on Roto Lock fittings. Complete steps 6 and 7
prior to pulling a vacuum.
System “Rack”
Replace Schraeder caps and Schraeder cores on the high side. All
Schraeder caps should be brass.
1 - Replace liquid line filters on the conversion date.
2 - Replace suction felts or cores on the conversion date.
3 - Use brass sealing caps on ball valves and compressor service valves.
4 - Set holdback valves on the condenser drain leg.
5 - Set evaporator pressure regulating valves to the manufacturer’s
parameters before setting any superheats.
6 - Set mechanical sub-coolers to the rack manufacturers’ parameters.
Verify the stable operation of the system before setting any
superheats.
7 - Set thermostatic expansion valve superheats to 8–10 K for medium
temperature applications and 5-7 K for low temperature
applications. With blended refrigerants use dew-point temperatures
for superheat measurements.
Retrofitting of R22 chillers
In recent years, R22 water chillers have been converted for use
with a hydrocarbon refrigerant (R290) in some installations in Asian
countries. Procedures used for conversion are similar to the general
procedures.
It must be stressed that it is of utmost importance to ensure that
the correct procedures are followed, that the technicians are trained
correctly and the right safety devices are in place.
Provided these requirements are carried out, a HC charged chiller
will offer a lifetime of service with reduced power consumption and
more efficient cooling.
Certain situations are such that HCs cannot be used for retrofitting chillers,
such as:
• Basement units with no option to ventilate
• Poorly maintained units with existing major problems
• Units adjacent to ignition sources that cannot be isolated
• Large units where the public have access.
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