Unit installation

803 C – 01/05 A – pag. 14/17
Preventive maintenance schedule
PERIODICITY
Operation
Ref. No.
TYPE OF OPERATION
Weekly Monthly
Six-
Monthly
Yearly
1
Reading and recording of suction pressure
x
2
Reading and recording of discharge pressure
x
3
Reading and recording of supply voltage
x
4
Reading and recording of current intensity
x
5
Check refrigerant charge and possible moisture in the
circuit refrigerant through the liquid sight glass
x
6
Check the suction temperature and the superheating
x
7
Check setting and operation of safety devices
x
8
Check setting and proper operation of control devices
x
9
Inspect the condenser for possible scaling or studging
x
Refrigerant
Refrigerant charging
PFS water cooled screw chillers are shipped factory charged with a full operating charge of refrigerant but there
may be times that a unit must be recharged at the jobsite. Follow these recommendations when field charging.
PFS water cooled screw chillers are more sensitive to under-charging than to overcharging therefore it is
preferable to be slightly overcharged rather than undercharged on a circuit. The optimum charge is the charge
which allows the unit to run with a solid stream of liquid in the liquid line at all operating conditions. When the liquid
line temperature does not drop with the addition of 2,2-4,5 Kg of charge then the subcooler is nearly full and
proper charge has been reached. If the liquid line temperature does not drop and the discharge pressure goes up
20,7-34,5 kPa as 2,2-4,5 Kg of refrigerant is added the correct maximum charge has been reached. Unit charging
can be done at any steady load condition, at any outdoor ambient temperature. Unit must be allowed to run 5
minutes or longer so that the condenser fan staging is stabilized at normal operating discharge pressure.
In case moisture is noticed in the system, through the moisture indicator, the system must be evacuated to
eliminate cause of trouble. After the evacuation, the system must be dried reducing it to an almost perfect vacuum.
For this purpose, a displacement vacuum pump should be used.
Any moisture and air left in the system will be absorbed by the dry nitrogen used to break the vacuum, and they
will be almost completely removed by the three evacuations.
If burnt oil or sludge are found in the refrigerant circuit (caused by the compressor motor burn-out), before the
vacuum operation it will be necessary to carefully clean the system using the filter dryer cleaneout method; which
basically involves the use of special filter dryers incorporating a suitable desiccant in both the liquid and suction
lines.
Excessive refrigerant losses can also leak oil from the system. Check the separator oil level during operation and
ensure that oil is visible in the top sightglass.
1. If the unit is slightly undercharged the unit will show bubbles in the sightglass. Recharge the unit.
2. If the unit is moderately undercharged the unit will most likely trip on freeze protection. Recharge the unit as
described in the charging procedure below.
Procedure to charge a moderately undercharged PFS unit
1. If a unit is low on refrigerant you must first determine the cause before attempting to recharge the unit. Locate
and repair any refrigerant leak. Evidence of oil is a good indicator of leakage however, oil may not be visible at
all leaks. Liquid leak detector fluids work well to show bubbles at medium size leaks but electronic leak detector
may be needed to locate small leaks.
2. Add the charge to the system through the schrader fitting on the tube entering the evaporator between the
expansion valve and the evaporator head.
3. The charge can be added at any load condition.