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13.1 REFRIGERANT CHARGE
13.1.1 Refrigerant replacement procedure with unit stopped and in vacuum (refrigerant charge in
the liquid phase)
Open the shut off valve as far as possible so that it closes the service coupling. Connect the refrigerant cylinder to the
service coupling without tightening the coupling. Half close the liquid shut off valve. If the circuit has been dehydrated and
is in vacuum, charge the liquid by turning the cylinder upside down. Weigh and charge the appropriate quantity. Open the
valve completely. Start up the unit and leave it running at full charge for some minutes. Check that the indicator is clear
with no bubbles. Make sure that the transparency condition without bubbles is due to the liquid and not to the vapour.
Correct functioning of the unit allows for overheating of 4 - 7° C and subcooling of 4 - 8°C. Values of overheating which are
too high may be caused by a lack of refrigerant, whereas high subcooling values may mean an excess of charge. After
intervention on the charge, it is appropriate to check that the unit runs within the declared values: with unit steadily running
on a full charge, measure the temperature of the suction line downstream of the thermostatic valve bulb; read the balance
pressure to the evaporator on the low pressure manometer and the corresponding saturation temperature.
Overheating is equal to the difference between the temperatures measured in this way. Then measure the temperature of
the liquid line coming out of the condenser and read the balance pressure to the condenser on the high -pressure
manometer and the corresponding saturation temperature. The subcooling is the difference between these temperatures.
Danger While refrigerant is being added do not exclude any control system and let the water circulate in the evaporator to
avoid the formation of ice.
High pressure
port
Low pressure
port
Vacuum meter
High pressure
gauge
Low
pressure
gauge
Refrigerant circuit diagram connection to vacuum pump
Page 27
Vacuum pump
Oil trap
Liquid sight glass
HP port
LP port
Scale
HP gauge
LP gauge
Refrigerant charge in the liquid phase
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