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4.14 - High Pressure (Maximum Condensing Temperature) Override
This function shall be used to avoid circuit high pressure trip while the condensing pressure reaches a configurable
override threshold (Service 1 Configuration).
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If the saturated condensing temperature is greater than the maximum condensing temperature (mct_sp) minus
the maximum condensing temperature override differential (mct_diff) but less than the maximum condensing
temperature (mct_sp) then the circuit capacity increase shall be inhibited.
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If the saturated condensing temperature is greater than the maximum condensing temperature (mct_sp) then the
circuit capacity shall be reduced. The first capacity stage shall never be turned off even if that causes a circuit
high pressure trip.
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If the circuit capacity has been reduced due to high condensing temperature override then the circuit capacity
increase will not be allowed for 5 minutes even if the saturated condensing temperature is below the maximum
condensing temperature (mct_sp) minus the maximum condensing temperature override differential. This shall
avoid compressor cycling.
4.15 - High Current Override
This function shall be used to avoid circuit high current trip while the motor current reaches a configurable override
threshold (Service 1 Configuration).
w
If the current is greater than the maximum current threshold (curr_max) minus the maximum current override
differential (curr_diff) but less than the maximum current threshold (curr_max) then the circuit capacity increase
shall be inhibited.
w
If the current is greater than the maximum current threshold (curr_max) then the circuit capacity shall be reduced
by removing a loader or the affected compressor.
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If the circuit capacity has been reduced due to current override then the circuit capacity increase will not be
allowed for 5 minutes what ever current measured. This shall avoid compressor cycling.
4.16 - Stopping Function
4.16.1- Stopping a compressor by capacity unloading
If the selected compressor is operating with at least one loader ON, then all the loaders in the same circuit shall be
de-energized for 15 seconds before stopping the compressor.
4.16.2- Stopping the unit by manual command (OFF)
Both circuit shall decrease its capacity progressively every 15 seconds. One loader is immediately de-energized. The
last loader will be de-energized in 15 seconds later. Then all compressors, oil solenoids and oil pump will be
de-energized in 15 seconds after the last loader is turned OFF.
Here is an example of the stopping function with time indicator for a circuit with both loaders ON before receiving a
STOP command.
t = t
0
loader_2 = OFF
t = t
0 + 15s
loader_1 = OFF,
t = t
0 + 30s
All the compressors, oil solenoids and oil pumps shall be de-energized
The exv shall be closed in one minute after the last compressor is de-energized or after the difference between
discharge and suction pressure is lower than 58 psi
note : Both circuits can be stopped in different timing depending on the status of their loaders when the
STOP command is received. Maximum duration for stopping the unit is 30 seconds. A circuit can be stopped
immediately if no loader is ON before going to stopping procedure.
4.16.3- Stopping a circuit by failure
If the circuit or the hole unit are failed by alarms freeze, low sst, cooler flow, all the compressors are shut off
immediately. Otherwise, it shall respect procedure above.
CARRIER SA
USER'S GUIDE FOR
30GX&HX PRO_DIALOG 4 V.2
ECG-UG-02-002
Rev: Original
Page: 48/98
©
C
ARRIER
S
.
A
NOT
TO
BE
DISCLOSED
TO
PERSONS
OUTSIDE
CARRIER
ORGANIZATION
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