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(0.1 to 0.7 bar). If oil pressure at the compressor drops
due to filter blockage, the differential pressure on the
display will increase and when the maximum limit is
reached the compressor will be shut down.
This safety is activated after 3 minutes of operation. Oil
pressure must be less than 65 PSID (4.4 bar) for R22
models as long as the compressor continues to run.
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 system
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
JOHNSON CONTROLS
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
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
temperature is above 225°F (107°C) for more than 3
seconds, the compressor will shut down.
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 refrig-
erant flow. A number of transient timer features prevent
nuisance trips during start-up, compressor loading, etc.
The Low Suction Pressure Safety is programmable (see
Section 8.2 / Page 161, Low Suction Pressure 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 cutout,
but must be greater than:
SP Cutout= Programmed Cutout X (run Time - 25)
This cutout value increases with time until after 225 sec-
onds it equals the programmed cutout value. If suction
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 seconds
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. 48 – SUCTION PRESSURE CUTOUT
FORM 201.18-NM7
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
LD07013A
139
8
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