York YVAA, Installation, Operation & Maintenance Instructions Manual, Page: 123 / 178

SECTION 7 - OPERATION
JOHNSON CONTROLS
123
FORM 201.28-NM1.1
ISSUE DATE: 1/31/2018
7
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 to 2.09 barg (0 PSID to 30
PSID) in 5 to 10 minutes based on ambient tempera-
ture. See the following table for the ramp times for the
given ambient temperatures.
TABLE 18 - 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 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
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
(0%) and for 5 minutes of operation if the economizer
feed valve is open greater than 0%. If the discharge su-
perheat falls below 2.8°C (5.0°F) for 5 minutes under
either condition, the system will shut down.
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.
Discharge Pressure Load Limiting/Unloading
Discharge pressure load limiting protects the con-
denser from experiencing dangerously high pressures.
A system is permitted to load normally as long as the
discharge pressure is below the High Discharge Pres-
sure Cutout minus 20 PSIG. Between Cutout minus
20PSIG and Cutout minus 15 PSIG loading is inhib-
ited even though increased loading may be required.
Between Cutout minus 15 PSIG and the Discharge
Pressure Cutout, forced unloading is performed every
2 seconds according to the following table. The dis-
charge pressure unload point is fixed at 255 PSIG.