Unit Safeties - York YCAL0019 Installation, Operation And Maintenance Manual

SECTION 7 – UNIT CONTROLS
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 3 shutdowns in 90 minutes, in-
dicating the system is locked out and will not restart.
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 follows. If the
actual feedback voltage of the system proportional to
currents exceeds the programmed trip voltage for 5
seconds, the system will shutdown.
This safety will shut down a system if either the suc-
tion 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
automatic 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 Temperature Cutout is a safety
shutdown designed to protect the chiller from operat-
ing in a low ambient condition. If the outdoor ambient
temperature falls below the programmable cutout, the
chiller will shut down. Restart can occur when tem-
perature rises 2 °F above the cutoff.
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M T R C U R R
M T R C U R R
F A U L T :
T E M P
U N I T
L O W L I Q U I D
The Low Leaving Chilled Liquid Temperature Cut-
out 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 programmed. Anytime the leaving chilled
liquid temperature (water or glycol) drops below the
cutout point, the chiller will shutdown. Restart can oc-
cur when chilled liquid temperature rises 2 °F above
the cutout.
U N I T
1 1 5 V A C U N D E R
The Under Voltage Safety assures that the system is
not operated at voltages where malfunction of the mi-
croprocessor could result in system damage. When the
115VAC to the micro panel drops below a certain level,
a unit fault is initiated to safely shut down the unit. Re-
start is allowed after the unit is fully powered again and
the anti-recycle timers have finished counting down.
U N I T
H I G H M T R
When the CURRENT FEEDBACK ONE PER UNIT
option is selected under the OPTIONS key, the unit will
shut down when the voltage exceeds the programmed
trip voltage for 5 seconds.
The trip voltage is programmed at the factory accord-
ing to compressor or unit RLA.
Restart will occur after the anti-recycle timer times out.
Unit Warning
The following messages are not unit safeties and will
not be logged to the history buffer. They are unit warn-
ings and will not auto-restart. Operator intervention is
required to allow a restart of the chiller.
! ! L O W B A T T E R Y
C H E C K P R O G / S E T P / O P T N
The Low Battery Warning can only occur at unit pow-
er-up. On micro panel power-up, the RTC battery is
checked. If a low battery is found, all programmed
setpoints, program values, options, time, schedule,
and history buffers will be lost. These values will all
FORM 150.67-NM1
ISSUE DATE: 4/28/2017
F A U L T :
T E M P
F A U L T :
V O L T A G E
F A U L T :
C U R R
! !
JOHNSON CONTROLS