JOHNSON CONTROLS
132
FORM 150.67-NM2
ISSUE DATE: 01/31/2019
SECTION 7 – UNIT CONTROL CENTER
U N I T F A U L T :
L O W A M B I E N T T E M P
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 F A U L T :
L O W L I Q U I D T E M P
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.
U N I T F A U L T :
1 1 5 V A C U N D E R V O L T A G E
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 F A U L T :
H I G H M T R C U R 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 pro-
grammed 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.
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 micro 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,
indicating the system is locked out and will not
restart.
S Y S 1 H I G H M T R C U R R
S Y S 2 H I G H M T R C U R R
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 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.
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