Specifications

56 YORK INTERNATIONAL
OIL RECOVERY
YS Chiller Best Practice Oil Recovery Method
A skilled service technician can recover oil from the
refrigerant charge in the evaporator in less than 60 min-
utes.
Before starting the chiller, print a History print. This
will help you determine the reason for the oil loss. The
operating conditions are stored in memory in a history
buffer file. Connect a printer and press the History
print key.
1. If the chiller was shut off on LOW OIL LEVEL
safety: Place a jumper wire between terminals 1
and 18 to satisfy the control circuit.
2. Start the chiller in AUTO mode of operation.
3. As soon as the chiller starts, remove the jumper
wire from between terminals 1 and 18. (This was
installed in Step 1.)
4. In the automatic mode of operation, the slide valve
will be force loaded to establish differential pres-
sure. A minimum pressure differential of 30 PSID
(oil supply pressure relative to evaporator pressure)
must be met within the first three minutes of chiller
operation or the chiller will be shut off on a LOW
PRESSURE safety.
If the entering condenser water is cold,
turn off the condenser pump or regu-
late that amount of water flowing
through the condenser to establish the
necessary pressure differential. Rec-
ommended, entering condenser water
temperature should be at least 15°F
or greater than the leaving chilled
water temperature.
5. Press the FILTER PRESSURE key and monitor
the DIFF PRESS as soon as the 30 PSID pressure
differential has been established. Press the UN-
LOAD key to unload the slide valve.
6. Calculate the compressor discharge superheat
(DSH).
Compressor DSH =
(Condenser Discharge Temperature)
– (Saturated Condensing Temperature
Monitor the compressor DSH. When the compressor
DSH is equal to, or greater than, 15ºF, press the LOAD
key for one second and then press the HOLD key.
7. Recalculate the compressor DSH. Do not increase
the slide valve position until the compressor DSH is
equal to, or greater than, 15ºF.
Refer to Figure 33. This is a compari-
son of the compressor DSH vs. Time
and Slide Valve Position vs. Time. This
plot is from a YSBBBBS1-CHD
chiller. Three additional gallons of oil
were added and all the oil was trans-
ferred from the oil separator into the
evaporator until the chiller shut off on
LOW OIL LEVEL safety. Use this
chart as a guide for oil recovery. Ac-
tual field conditions will determine
how large the slide valve incremental
increase can be to maintain compres-
sor DSH of 15ºF or greater.
The process of recovering oil from the refrigerant
charge is dependent on compressor DSH, time and
slide valve position.
During the initial phase of the oil recovery process, the
slide valve position can not be increased more than 2%
- 3% without lowering the compressor DSH to below
10ºF. If the slide valve position is increased too rapidly,
the increase in compressor suction velocity will entrain
oil/refrigerant foam with the suction gas. The entrained
oil/refrigerant foam will lower the compressor discharge
temperature and the compressor DSH to less than 10ºF.
If the compressor DSH is less than 10ºF, an EXCESS
CHARGE OVERRIDE protection is initiated and the
slide valve will be automatically unloaded. Further load-
ing of slide valve will be inhibited until the compressor
DSH increases to above 15ºF.
Notice the sequence of events that begin at the nine-
minute interval on Figure 33. The technician increases
the slide valve position from 8% to 13%. This incre-
mental change was too large - notice the compressor
DSH is reduced from 17.8ºF to 9.9ºF. Since the EX-
CESS CHARGE OVERRIDE threshold of 10ºF was
exceeded, the slide valve was automatically unloaded
to 0%. Beginning at the eleven-minute interval, the
technician was careful to maintain compressor DSH
at higher levels until the oil was recovered.
As more oil is removed from the refrigerant, larger incre-
mental slide valve increases are possible, and the com-
pressor DSH will remain above 15ºF. Be patient, let
Maintenance