JOHNSON CONTROLS
85
SECTION 6 - OPERATION
FORM 201.30-ICOM1 (519)
ISSUE DATE: 05/22/2019
6
• A low leaving chilled liquid temperature fault
occurs.
• The VSD is requested to precharge for a run.
• The DAILY SCHEDULE is on and the UNIT
SWITCH is on.
• The leaving condenser liquid temperature is
less than (<) 36°F (< 2.2°C).
Regardless if any condition (above) is true, the pump
will not run if the control panel has been powered up
for less than 30 seconds, or if it has run in the last 30
seconds to prevent the pump motor from overheating.
Compressor Heater Control
The compressor has its own heater. The purpose of the
heater is to make sure refrigerant does not condense
in the compressor. There is no oil sump, but refriger-
ant could possibly condense in the rotors or the motor
housing. The heater will be off whenever the compres-
sor is running. As soon as the compressor shuts off,
the heater will turn on as long as all motor temperature
sensors in the compressor read less than 158°F (70°C) .
The heater will turn off, if any internal compressor mo-
tor temperature sensor reads more than 160°F (71.1°C).
Alarms
The system has its own alarm contacts for custom-
er remote communication. The alarm output is on
(dry contact closed) when no fault condition is pres-
ent and off (dry contact open) to indicate an alarm
situation. The alarm will be activated (contacts open),
if any condition below is true.
• Unit is faulted or inhibited from starting for more
than ve seconds.
• Unit is locked out.
• Power is removed from the chiller.
Chiller Run Contact
The chiller run dry contact is closed whenever the com-
pressor is running, and open when the compressor is shut
off.
Chilled and Condenser Liquid Flow Switches
The chilled and condenser liquid flow switches must
have electrical continuity to Terminal 2 to permit the
chiller to run.
Remote Run Permissive Input
The run permissive switches must have electrical con-
tinuity to Terminal 2 to permit the chiller to run.
Load Limiting
Load limiting controls exist and continually supervise
the operation to avoid a system from reaching a safety
trip level. Load limiting controls act when any param-
eter listed in Table 28 on page 86 approaches its
safety shutdown threshold to prevent additional load-
ing by the capacity control logic. Override unload con-
trols act when a parameter goes beyond the load limit
threshold and is close to the safety shutdown threshold
to unload the chiller regardless of the capacity control
logic. All of these controls are active immediately at
start-up. The following graph in Figure 46 on page
85 represents the control operation.
FIGURE 46 - CONTROL OPERATION
LD16440
The normal operating region of the parameter is to the
left of the X point, with the value of the parameter ap-
proaching its limit heading right toward Y and Z. For
example, increasing condenser pressure, or decreasing
evaporator pressure is represented moving to the right.
Prior to reaching the X point capacity control is not
limited, and is allowed to load and unload as needed.
Load limiting prevents capacity control from load-
ing when the parameter value is between the X and Y
points. Capacity control is still allowed to unload as
needed. When the value is between the Y and Z points,
capacity control is overridden and the compressor is
unloaded by the load limiting function based on a lin-
ear ramp between the two points. The thresholds for
each parameter is provided in Table 28 on page 86.
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