York YCAS Series, Installation Operation & Maintenance

Page: 153 / 216

153 YORK INTERNATIONAL
FORM 201.19-NM8 (804)
Low Suction Pressure Cutout:
The Low Suction Pressure Cutout aids in protecting
the evaporator from damage due to ice build up caused
by operation at low refrigerant charge or restricted
re frig er ant flow. A transient timer feature pre vents
nuisance trips during start-up, compressor load ing, etc.
The Low Suction Pressure Safety is pro gram ma ble (see
Section 8.2 / Page 179, Low Suction Pres sure Cutout
for more details).
The suction pressure cut-out is ignored for the fi rst 45
seconds of operation. During the next 180 seconds of
running, suction pressure may be lower than the cut out,
but must be greater than:
SP Cutout= Programmed Cutout X (run Time - 25)
200
This cutout value increases with time (10% to 100%)
until after 225 seconds it equals the programmed cut-
out value. If suc tion pressure falls below the calculated
cutout value before 225 seconds of run time, the system
will be shut down.
The following graph shows a typical programmed suc-
tion pressure cutout of 44 PSIG (3 bar) and its change
from time = 0 sec of compressor run time to 225 sec onds
of compressor run time.
Low Oil Differential Pressure Cutout:
The Low Oil Pressure Differential Safety assures the
compressor receives proper lubrication by monitoring
the differential between oil pressure returning to the
compressor and suction pressure. Lack of a differential
indicates that the compressor is not pumping and no oil
is being pumped through the compressor to lubricate
the bearings and rotors.
This type of oil failure will not be picked up by the High
Oil Differential Safety since no fl ow will cause the dif-
fer en tial through the oil piping to drop to zero.
During normal operation, differential oil pressure must
be greater than 50 PSID. At start-up, the cut-out is
ramped over time according to ambient temperature.
For ambients above 50°F (10°C), the Low Oil Dif fer -
en tial Safety is activated after 1 minute of compressor
operation when the oil pressure differential must be
great er than 10 PSID (.7 bar). After 2 minutes it must
be greater than 20 PSID (1.4 bar); after 3 minutes, 30
PSID (2 bar); after 4 minutes, 40 PSID (2.7 bar); and
from 5 minutes of operation and onwards, oil pressure
must remain higher than 50 PSID (3.4 bar) or the sys tem
will be shut down. For lower ambients, the linear ramp
times are as follows:
AMBIENT TEMP RAMP TIME
>50°F (10°C) 5 Minutes
>45°F (7°C) 6 Minutes
>40°F (4°C) 7 Minutes
>35°F (2°C) 8 Minutes
>30°F (-1°C) 9 Minutes
<=30°F (-1°C) 10 Minutes
High Oil Temperature Cutout:
This safety assures oil temperature does not exceed a safe
operating temperature which affects compressor lubrica-
tion. Typical oil temperature during normal op er a tion
will be approximately 130 - 150°F (54 - 66°C).
The High Oil Temperature Safety is activated after 2
minutes of compressor operation, after which if oil
tem per a ture is above 225°F (107°C) for more than 3
sec onds, the compressor will shut down.
Suction Pressure Cutout With
44 PSIG Programmed Cutout
LD07013
FIG. 75 –
SUCTION PRESSURE CUTOUT
S Y S # L O W S U C T P R E S S
S Y S # L O W S U C T P R E S S
0 30 60 90 120 150 180 210 240 270 310
45
40
35
30
25
20
15
10
5
0
Run Time (seconds)
Suction Pressure Cutout
S Y S # L O W O I L D I F F
S Y S # L O W O I L D I F F
S Y S # H I G H O I L T E M P
S Y S # H I G H O I L T E M P
8