Unit Safeties - York YCWL0056SE Installation Operation & Maintenance

SECTION 7 – UNIT CONTROLS
The internal motor protector opens at 185 °F to 248 °F
(85 °C to 120 °C) and auto resets. On 60 Hz chillers,
the mechanical HP switch opens at 500 PSIG plus or
minus 8 PSIG and automatically closes at 375 PSIG
plus or minus 10 PSIG.
On 50Hz chillers, the manual reset HP switch opens
at 503 PSIG (34.7 barg). On systems with a second
tool reset cutout, the tool reset HP switch opens at 532
PSIG (36.7 barg).
The compressor is also equipped with a discharge
temperature sensor for the purpose of sensing inter-
nal scroll temperature. This sensor protects the scrolls
from overheating due to inadequate cooling that may
occur when refrigerant charge is low, or superheat is
too high.
When the sensor senses a high temperature, it opens
the motor protector circuit in the compressor causing
the compressor to shut down.
During the first two faults an MP/HP INHIBIT message
will be displayed and the system will not be locked out.
Only after the third fault in 90 minutes will the MP/
HPCO FAULT message be displayed.
Whenever the motor protector or discharge sensor
shuts down a compressor and the system, the inter-
nal compressor contacts will open for a period of 30
minutes to assure that the motor or scroll temperatures
have time to dissipate the heat and cool down. The MP/
HP INHIBIT message will be displayed while these
contacts are open or when the HPCO is open. While
this message is displayed, the compressors will not be
permitted to start.
After 30 minutes, the contacts will close and the sys-
tem will be permitted to restart. The microprocessor
will not try to restart the compressors in a system that
shuts down on this safety for a period of 30 minutes to
allow the internal compressor to time out.
During the 30 minute timeout, the MP/HPCO INHIB
message will be displayed. The MP/HPCO FAULT will
only be displayed after three shutdowns in 90 minutes,
indicating the system is locked out and will not
restart.
120
S Y S 1 H I G H
S Y S 2 H I G H
When the SYSTEM CURRENT FEEDBACK option
is installed and selected (Option 11 under OPTIONS
key Current Feedback), this safety will operate as fol-
lows. If the actual feedback voltage of the system pro-
portional to currents exceeds the programmed trip volt-
age for 5 seconds, the system will shutdown.
This safety will shut down a system if either suction
temperature or suction pressure sensors read out of
range high or low. This condition must be present for 3
seconds to cause a system shutdown. The safety locks
out a system after the first fault and will not allow au-
tomatic restarting.

Unit Safeties

Unit safeties are faults that cause all running compres-
sors to be shut down. Unit faults are auto reset faults
in that the unit will be allowed to restart automatically
after the fault condition is no longer present.
U N I T
L O W A M B I E N T
The Low Ambient Temp Cutout is a Safety Shutdown
designed to protect the chiller from operating in a low
ambient condition. If the outdoor ambient temperature
falls below the programmable cutout, the chiller will
shut down. Restart can occur when temperature rises 2
°F above the cutoff.
U N I T
L O W L I Q U I D
The Low Leaving Chilled Liquid Temp Cutout protects
the chiller form an evaporator freeze-up should the
chilled liquid temperature drop below the freeze point.
This situation could occur under low flow conditions or
if the micro panel setpoint values are improperly pro-
grammed. Anytime the leaving chilled liquid tempera-
ture (water or glycol) drops below the cutout point, the
chiller will shutdown. Restart can occur when chilled
liquid temperature rises 2 °F above the cutout.
FORM 201.26-NM1
ISSUE DATE: 1/19/2018
M T R C U R R
M T R C U R R
F A U L T :
T E M P
F A U L T :
T E M P
JOHNSON CONTROLS