Johnson Controls YEWS Series, Installation, Operation And Maintanance Instructions

Page: 58 / 88

If the unit is running with a load lower than 20% rated
load, it may caused the depressing of the oil level due to
the low condensing temperature. In that case, the oil does
not leak out, it is carried out to the condenser by the
refrigerant flow and finally the oil will enter the
evaporator and accumated. However, if the oil in the
evaporator accumulate to a certain amount , it may cause
operation problems.
If the discharge superheat is lower than 5
℃
, it may cause
some trouble to the oil system. Discharge superheat
temperature is equal to disharge temperature minus to the
condensing temperature.The most suitable refrigerant
charge is decided by the diacharge superheat and the
evaporator approach.
If the unit can not be loaded normally, it is possible that
the lubricant in the evaporator is excessive. Where there is
too much oil in the refrigerant, the liquid level will blister
and the mixture of oil and liquid refrigerant will be
carried to the compressor, which decreases the discharge
superheat.If the discharge superheat decreases to a value
lower than 5
℃
, the compressor will compulsily unload
and decrease the cooling capacity unless the discharge
superheat rise up to 5
℃
and keep higher than 5
℃
for
more than 60 seconds.
The excessive charge amount of refrigerant will also
decrease the discharge superheat temperature, and cause
the the unit fail to load normarly. So refrigerant should be
adjusted to a suitable amount(Ensure the discharge superheat
temperature in the range of 6-10
℃
in rating conditions)
Fault treatment
If the unit stop for fault, the operator should handle the fault
in time, if it can not be solved, please contact the YORK
service personnel immediately. No attempt should be done
to start the chiller continuously when it is stop due to fault
otherwise it would cause damage to the chiller.
Running log
The running situation should be permanently recorded
according to the regulated time interval in each 24 hour
running cycle.
The following table is the duty record table of WORK for
unit examination.
Please record every data correctly, because it is reference for
engineer to judge the running conditions.The record values
by testing a new unit can be set as the normal situation,
which can be compared with the later record value.
For example, if the difference between the leaving cooling
water temperature and condensing temperature is higher
than the normal value, it shows that the water side of
condenser may be too dirty.
Running detection
By performing the periodical detection and maintenance
according to the value displayed in the display interface of
control center, the operator can avoid the serious running
fault. The following is the guide for detection content and
method.
7.4 Other notes
At any times, the unit will stop once the OFF key in the
keyboard is pressed, then the oil heater will be Powered on
and keep a high oil temperature to prevent refrigerant
dissolving into the oil.
In order to prevent the damage to chiller, the chiller should
YEWS-E Water Cooling Screw Chiller/Heat Pump
53