Daikin FDYM20JEVLK [22/30] Special precautions when charging unit with scroll compressors

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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 R410A refrigerants but are not applied to

others competitive Scroll compressors.

Scroll compressors have a very high volumetric efÀ ciency and quickly pump a deep vacuum if there is insufÀ cient 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 Á anks 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 À rst few hours or the damage done during À eld charging may show up some time later. Other typical À eld 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 À eld charging. The minimum equipment required to do a satisfactory job is:-

1. Set of service gauges 4. Vacuum gauge

2. Hoses 5. Scales

3. Vacuum pump 6. 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 -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 Á ows 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.

Dip-pipe

Liquid withdrawal

Invert cylinder

without dip-pipe

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