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9. SPECIAL PRECAUTIONS WHEN CHARGING UNIT WITH SCROLL COMPRESSORS
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These precautions are intended for use with scroll compressors only with R22, R407C, R 134A, R404A, R507 and
R41 0A refrigerants but are not applied to reciprocating compressors or competitive scroll compressors.
Scroll compressors have a very high volumetric efficiency and quickly pump a deep vacuum if there is insufficient
refrigerant in the system or if refrigerant is added too slowly. Operation with low suction pressure will quickly lead
to very high discharge temperatures. While this process is happening, the scrolls are not being well lubricated -
scrolls depend on the oil mist in the refrigerant for lubrication. A lack of lubrication leads to high friction between
the scroll flanks and tips and generates additional heat. The combination of heat of compression and heat from
increased friction is concentrated in a small localized discharge area where temperatures can quickly rise to more
than 300'C. These extreme temperatures damage the Scroll spirals and the orbiting Scroll bearing. This damage
can occur in less than one minute especially on larger compressors. Failure may occur in the first few hours or the
damage done during field charging may show up some time later.
Other typical field charging problems include undercharging, overcharging, moisture or air in the system etc. In
time each one of these problems can cause compressor failure.
Minimal equipment is required for field charging. The minimum equipment required to do a satisfactory job is:-
Set of service gauges
Vacuum gauge
Hoses
Scales
Vacuum pump
Thermometer
The proper refrigerant charge should follow the volume as recommended by manufacturer and recommendation
should be followed by the installer.
1. Charging procedures - Single phase compressors
Evacuate the system to 500 microns Hg (67Pa). To reduce evacuation time, use short, large diameter hoses
and connect to unrestricted service ports on the system. Quality of vacuum cannot be determined by time - a
reliable vacuum gauge must be used. (eg. electronic vacuum gauge)
Turn the refrigerant cylinder upside down, purge the charging hose and charge liquid through the liquid line
charging port until refrigerant no longer flows or until the correct charge has been weighed in. If additional
charge is required, start the system and slowly bleed liquid into the suction side until the system is full.
It is recommended to charge liquid refrigerant
in
a CONTROLLED manner into the suction side until the
s
ystem is full.
This recommendation does not hold true for reciprocating compressors where liquid charging
into the suction side could cause severe damage.
Carefully monitor the suction and discharge pressures - ensure that the suction pressure does not fall below
25 psig (1.7 bar) at any time during the charging process.
There are many ways of charging liquid in a "controlled manner'' into the
suction side:-
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1. Use valve A on the manifold gauge set
2. Use the valve on the refrigerant cylinder
3. Charge through a Shredder valve
4. Use a hose with a Shredder valve depressor
5. Charge into the suction side at some distance from the compressor
2. Charging procedures - Three phase compressors
The fundamental procedure is the same as for single phase models but the compressor can run in the wrong
direction on starting. If this happens reverse any two phases and start again. Short term reverse rotation will
not damage the compressor.
All Scroll Compressors have internal discharge temperature protectors which are very effective in
preventing dangerously high discharge temperatures during charging. The protection module will trip and lock
the compressor out for 30 minutes. It is not normally necessary to wait 30 minutes for the module to
reset. When the compressor has cooled down, the module can be reset by breaking the power supply to
the control circuit. Very often the serviceman does not understand why the module tripped and uses a
jumper wire to bypass it. He continues to charge the system and removes the jumper when charging is
complete. The compressor may or may not run with the protector back in the circuit but it is certain that the
compressor has been damaged and premature failure is inevitable.
Caution for refrigerant leaks
This system uses R41 0A as refrigerant . R41 0A itself is an entirely safe, non toxic, non- combustible refrigerant .
Nevertheless care must be taken to ensure that air conditioning facilities are installed in a room which is sufficiently
large. This assures that the maximum concentration level of refrigerant gas is not exceeded, in the unlikely event of
major leak in the system and this in accordance to the local applicable regulations and standards.
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