120 YORK INTERNATIONAL
FORM 201.18-NM1 (102)
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-
frigerant flow. A number of transient timer features pre-
vent nuisance trips during start-up, compressor load-
ing, etc. The Low Suction Pressure Safety is program-
mable (see Section 8.2, page 143, Low Suction Pres-
sure Cutout for more details).
The suction pressure cutout 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)
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.
Low Oil Differential Pressure Cutout:
The Low Oil Pressure Differential Safety ensures 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 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 ensures 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.
Suction Pressure Cutout With
44 PSIG Programmed Cutout
LD03525
FIG. 50 – SUCTION PRESSURE CUTOUT
After 225 seconds of operation with suction pressure
operating above the cutout, a 30 second transient timer
prevents short term fluctuations in suction pressure due
SYS # LOW SUCT PRESS
SYS # LOW SUCT PRESS
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
SYS # LOW O I L D I FF
SYS # LOW O I L D I FF
SYS # H I GH O I L TEMP
SYS # H I GH O I L TEMP
Micro Panel Contents
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