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SPECIAL PRECAUTIONS WHEN CHARGING UNIT WITH SCROLL COMPRESSORS
These precautions are intended for use with Scroll compressors only with R22 and R407C refrigerants but are not applied to
others 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:-
ADDITIONAL CHARGE
The refrigerant is pre-charge in the outdoor unit. If the piping length is less than 7.5m, then additional charge after vacuuming
is not necessary. When the piping length is more than 7.5m, use the table below.
R22
R407C
Liquid pipe OD
Additional charge kg/m
Additional charge kg/m
3/8"
0.06
0.05
1/2"
0.10
0.10
5/8"
0.16
0.15
3/4"
0.25
0.23
Set of service gauges
Hoses
Vacuum pump
1.
2.
3.
Vacuum gauge
Scales
Thermometer
4.
5.
6.
The proper refrigerant charge should follow the volume as recommended by manufacturer and recommendation should be
followed by the installer.
Charging procedures – Single phase compressors
Evacuate the system to -760mmHg. 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.
(etc. 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 recommends charging liquid in a CONTROLLED manner into the suction side until the system 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.
1.
NOTE
The additional refrigerant charge amount recommended is a guideline for long piping application.
The actual charge required may be different from the guideline due to different application and variation in site conditions.
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