Low Differential Oil Pressure Cutout Fault; High Discharge Temperature Cutout Fault; Low Discharge Superheat Cutout Fault; Discharge Pressure Load Limiting/Unloading - Quantech QTC4 STYLE A Series Installation Operation & Maintenance

SECTION 7 - OPERATION

Low Differential Oil Pressure Cutout Fault

The Low Differential Oil Pressure Cutout protects the
compressor from low oil flow and insufficient lubrica-
tion. A system will fault and shut down with a controlled
ramped shutdown when it's differential between oil
and suction pressure falls below the cutout. This safety
assures that the compressor is pumping sufficiently to
push oil through the oil cooling circuit and through the
internal compressor lubrication system. The Status dis-
play fault message for this safety is shown below:
SYS X YYYYYYYY LOW DIFF OIL PRESSURE
The X indicates the system and YYYYYYY indicates
the system is in a "FAULT" condition and will restart
when the 120 second anti-recycle timer times out or
"LOCKOUT" and will not restart until the operator
clears the fault using the keypad.
The safety is ignored for the first 60 seconds of run
time. After the first 60 seconds of operation, the
cutout is linearly ramped from 0 barg to 2.09 barg
(0 PSID to 30 PSID) in 5 to 10 minutes based on ambi-
ent temperature. See the following table for the ramp
times for the given ambient temperatures.
TABLE 17 - LOW DIFFERENTIAL OIL PRESSURE
CUTOUT
AMBIENT TEMPERATURE
more than 10°C (50ºF)
more than 7.2°C (45ºF)
more than 4.4°C (40ºF)
more than 1.6°C (35ºF)
more than 1.1°C (30ºF)
more than or equal to 1.1°C (30ºF)
A 30 second safety bypass below 50 Hertz is employed
during rampdown. The bypass is primarily needed
under conditions where another compressor is be-
ing brought on and the running compressor is being
ramped down to 5 Hertz to add the additional compres-
sor due to load requirements. Under these conditions,
the slow speed of the running compressor(s) causes the
oil differential to become very low, especially if the
water temperature is high and the suction pressure is
high. The bypass assures the compressor(s) will not
trip on a nuisance low oil differential fault.

High Discharge Temperature Cutout Fault

112
The High Discharge Temperature Cutout protects the
motor and compressor from overheating. A system will
fault and shut down with a controlled ramped shutdown
when its Discharge Temperature rises above 121°C
(250°F). A system will also be inhibited from starting if
the discharge temperature is above 93°C (200°F). The
Status display fault message for this safety is shown
below:
SYS X YYYYYYYY HIGH DISCHARGE TEMP
The X indicates the system and YYYYYYY indicates
the system is in a "FAULT" condition and will restart
when the 120 second anti-recycle timer times out or
"LOCKOUT" and will not restart until the operator
clears the fault using the keypad.

Low Discharge Superheat Cutout Fault

The Low Discharge Superheat safety helps protect the
compressor from liquid floodback through the econo-
mizer line due to a high flashtank level. It also helps
protect the compressor from excessive oil in circula-
tion due to excess oil charge in the system. Excessive
oil in circulation brings back liquid refrigerant which
is entrained in the oil. The liquid then drops out once it
enters the compressor.
The safety is ignored for the first 10 minutes of op-
eration if the system economizer feed valve is closed
RAMP
(0%) and for 5 minutes of operation if the economizer
TIME
feed valve is open greater than 0%. If the discharge su-
5 Minutes
perheat falls below 2.8°C (5.0°F) for 5 minutes under
6 Minutes
either condition, the system will shut down.
7 Minutes
8 Minutes
The X indicates the system and YYYYYYY indicates
the system is in a "FAULT" condition and will restart
9 Minutes
when the 120 second anti-recycle timer times out or
10 Minutes
"LOCKOUT" and will not restart until the operator
clears the fault using the keypad.

Discharge Pressure Load Limiting/Unloading

Discharge pressure load limiting protects the condens-
er from experiencing dangerously high pressures. A
system is permitted to load normally as long as the dis-
charge pressure is below the High Discharge Pressure
Cutout minus 20 PSIG. Between Cutout minus 20PSIG
and Cutout minus 15 PSIG loading is inhibited even
though increased loading may be required. Between
Cutout minus 15 PSIG and the Discharge Pressure Cut-
FORM QTC4-NM1
ISSUE DATE: 4/2/2018
QUANTECH