Specifications

60
JOHNSON CONTROLS
Form 201.28-NM1.EN.PED/CE (0211)
OPERATION
Low Differential Oil Pressure Cutout Fault
The Low Differential Oil Pressure Cutout protects the
compressor from low oil flow and insufficient lubrication.
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
display fault message for this safety is shown below:
SYS X FAULT: LOW DIFF OIL PRESSURE
The X indicates the system and FAULT 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 barD to 2.09 barD (0 PSID to 30
PSID) in 5 to 10 minutes based on ambient temperature.
See the following table for the ramp times for the given
ambient temperatures.
TABLE 4 - LOW DIFFERENTIAL OIL PRESSURE
CUTOUT
AMBIENT TEMPERATURE
RAMP
TIME
more than 10°C (50ºF) 5 Minutes
more than 7.2°C (45ºF) 6 Minutes
more than 4.4°C (40ºF) 7 Minutes
more than 1.6°C (35ºF) 8 Minutes
more than -1.1°C (30ºF) 9 Minutes
more than or equal to -1.1°C (30ºF) 10 Minutes
A 30 second safety bypass below 50 Hertz is employed
during rampdown. The bypass is primarily needed under
conditions where another compressor is being brought
on and the running compressor is being ramped down
to 5 Hertz to add the additional compressor 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
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 FAULT: HIGH DISCHARGE TEMP
The X indicates the system and FAULT 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
economizer line due to a high flashtank level. It also
helps protect the compressor from excessive oil in
circulation 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 operation
if the system economizer feed valve is closed (0%) and
for 5 minutes of operation if the economizer feed valve
is open greater than 0%. If the discharge superheat falls
below 2.8°C (5.0°F) for 5 minutes under either condition,
the system will shut down.
SYS X FAULT: LOW DISCHARGE SUPERHEAT
The X indicates the system and FAULT 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.