SECTION 7 - OPERATION
QUANTECH
113
FORM QTC4-NM1
ISSUE DATE: 4/2/2018
7
out, forced unloading is performed every 2 seconds ac-
cording to the following table. The discharge pressure
unload point is fixed at 255 PSIG.
TABLE 18 - DISCHARGE PRESSURE LOAD LIMIT-
ING/UNLOADING
DISCHARGE PRESSURE UN-LOADING
Discharge Pressure Cutout- 20
PSIG and Discharge Pres-
sure Cutout- 15 PSIG
0 Hz
Discharge Pressure Cutout- 13.5 PSIG 1 Hz
Discharge Pressure Cutout- 12 PSIG 2 Hz
Discharge Pressure Cutout- 10.5 PSIG 3 Hz
Discharge Pressure Cutout- 9 PSIG 4 Hz
Discharge Pressure Cutout- 7.5 PSIG 5 Hz
Discharge Pressure Cutout- 6 PSIG 6 Hz
Discharge Pressure Cutout- 4.5 PSIG 7 Hz
Discharge Pressure Cutout- 3 PSIG 8 Hz
Discharge Pressure Cutout- 1.5 PSIG 9 Hz
Discharge Pressure Cutout- 0 PSIG 10 Hz
Suction Pressure Load Limiting/Unloading
Suction pressure load limiting helps to protect the
evaporator from freezing. A system is permitted to load
normally as long as the Suction Pressure is above the
Suction Pressure Cutout plus 2 PSIG. Between Cut-
out plus 2 PSIG and the Cutout, loading is inhibited,
even though increased loading is required. Between the
Suction pressure Cutout and Suction Pressure Cutout
minus 10 PSIG, forced unloading is performed every
2 seconds according to . This situation would occur if
the suction pressure cutout transient override control is
in effect (Refer to Low Suction Pressure Cutout (Soft-
ware) Fault on Page 111). The suction pressure cutout
is programmed under the PROGRAM key. The default
Suction Pressure Cutout is set at 24.0 PSIG.
Suction pressure load limiting is active at startup, to
only prevent loading of the compressors. Suction pres-
sure limit unloading will not occur until the system run
time reaches 5 minutes of operation to allow the system
to stabilize.
TABLE 19 - SUCTION PRESSURE LOAD LIMITING/
UNLOADING
SUCTION PRESSURE UN-LOADING
Suction Pressure is between
Cutout +2 PSIG and Suc-
tion Pressure Cutout
0 Hz
Suction Pressure Cutout- 1 PSIG 1 Hz
Suction Pressure Cutout- 2 PSIG 2 Hz
Suction Pressure Cutout- 3 PSIG 3 Hz
Suction Pressure Cutout- 4 PSIG 4 Hz
Suction Pressure Cutout- 5 PSIG 5 Hz
Suction Pressure Cutout- 6 PSIG 6 Hz
Suction Pressure Cutout- 7 PSIG 7 Hz
Suction Pressure Cutout- 8 PSIG 8 Hz
Suction Pressure Cutout- 9 PSIG 9 Hz
Suction Pressure Cutout- 10 PSIG 10 Hz
Sensor Failure Cutout Fault
The Sensor Failure Cutout prevents the system from
running when a critical sensor (transducer, level sen-
sor, or motor winding temp sensor) is not function-
ing properly and reading out of range. This safety is
checked at startup and will prevent the system from
running if one of the sensors has failed.
The sensor failure safety will also fault and shutdown
a system while in operation, if a safety threshold is ex-
ceeded or a sensor reads out of range (high or low).
Following is the Status display fault message.
SYS X YYYYYYYY SENSOR FAILURE:
ZZZZZZZZZZZZ
The X indicates the specific system.
YYYYYYYY will either indicate the system
is in a “FAULT” condition and will restart
when the fault clears, or “LOCKOUT”
after 3 faults and will not restart until the
operator clears the fault using the keypad.
ZZZZZZZZZZZ indicates the failed sensor below:
• SUCT PRESS
• OIL PRESS
• DSCH PRESS
• MOTOR TEMP X *
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