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2
D
escription
The P45 series is a differential pressure switch
which senses the oil pressure and the suction
pressure on compressors using non corrosive
refrigerant.
When the compressor is started, the time delay
switch is energised. If the net oil pressure does
not build up to the "heater-off" point of the
control within the required time limit, the time
delay switch trips to stop the compressor. If the
net oil pressure rises to the "heater-off" point
within the required time after the compressor
starts, the time delay switch is automatically de-
energised and the compressor continues to
operate normally. If the net oil pressure should
drop below the "heater-on" setting during the
running cycle, the time delay switch is energised
and, unless the net oil pressure returns to
heater "off" point within the time delay period,
the compressor will be shut down. The
compressor can never run more than the
predetermined time on subnormal oil pressure.
F
unction
A. During start-up the lube-oil pressure is built
up to the control setpoint plus the
mechanical differential, before elapse of the
delay period
. Then the time delay heater is
de-energised. i.e. normal oil conditions have
been established.
B. During start-up the lube-oil pressure does
not build up a pressure to the setpoint plus
mechanical switch differential level before
the end of the delay period
compressor will stop. Terminal A, when
connected to a signal will be activated.
C. During running period the lube-oil pressure
falls to a value lower than the setpoint (cut-
out). The timer will be activated.
D. The lube-oil pressure reaches the setpoint
plus mechanical switch differential value
before the delay period
heater will be de-energised. The compressor
lube-oil conditions are normal again.
E. The lube-oil pressure falls to a lower value
than the setpoint (cut-out). The timer will be
activated.
Catalogue Section 6
. The
elapses. The
F. The lube-oil pressure remains at a lower
value than the setpoint plus the mechanical
differential during the delay period
compressor will stop. Terminal A, when
connected to a signal will be activated.
Restart can only be performed after about 5
min. by means of pushing the reset button,
provided the cause of the fault has been
determined.
∆ P
A
B
1
2
Fig. 1a
During start up
∆ P
D
C
1
<2
Fig. 1b
During operation
Setpoint in bar (factory set see data label)
Time delay in s. (see data label)
S
ystem Check
It is important that the function check be made
to insure that the differential pressure control is
operating correctly. This check can be made by
pressing the lever on the right side of the control
for a period corresponding to the delay time.
When the test is correctly executed the
compressor stops after the delay time
determined by the time delay has elapsed.
P45
Issue 9701
The
t
E
F
=2
© 1997 Johnson Controls Inc.
Order No. PD-P45-E
t
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