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Low Oil Differential Pressure Cutout:
S Y S
#
L O W
S Y S
#
L O W
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 flow will cause
the differential through the oil piping to drop to zero.
EXAMPLE:
For ambients above 50°F (10°C), the Low Oil Differ-
ential Safety is activated after 1 minute of compressor
operation when the oil pressure differential must be
greater 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
>50°F
(10°C)
>45°F
(7°C)
>40°F
(4°C)
>35°F
(2°C)
>30°F
(-1°C)
<=30°F
(-1°C)
High Oil Temperature Cutout:
S Y S
#
H I G H
S Y S
#
H I G H
This safety assures oil temperature does not exceed a
safe operating temperature which affects compressor
lubrication. Typical oil temperature during normal op-
eration 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-
perature is above 225°F (107°C) for more than 3 sec-
onds, the compressor will shut down.
YORK INTERNATIONAL
O I L
D I F F
O I L
D I F F
RAMP TIME
5 Minutes
6 Minutes
7 Minutes
8 Minutes
9 Minutes
10 Minutes
O I L
T E M P
O I L
T E M P
Low Suction Pressure Cutout:
S Y S
#
L O W
S Y S
#
L O W
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-
frigerant flow. A number of transient timer features
prevent nuisance trips during start-up, compressor load-
ing, etc. The Low Suction Pressure Safety is program-
mable (see Section 8.2 / Page 177, Low Suction Pres-
sure Cutout for more details).
The suction pressure cut-out is ignored for the first 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)
This cutout value increases with time until after 225
seconds it equals the programmed cutout 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.
45
40
35
30
25
20
15
10
5
0
0
30
60
90
120
Run Time (seconds)
Suction Pressure Cutout With
44 PSIG Programmed Cutout
FIG. 73 – SUCTION PRESSURE CUTOUT
After 225 seconds of operation with suction pressure
operating above the cut-out, a 30 second transient timer
prevents short term fluctuations in suction pressure due
FORM 201.18-NM3
S U C T
P R E S S
S U C T
P R E S S
25
150
180
210
240
270
310
LD03525
153
8
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