Controls Interface
11 2 RTAC-SVX01J-EN
Start Inhibited by Low Cond Temp
The chiller is inhibited from starting by Low Condenser Temperature- Inhibit is active below
either 25°F (can be disabled with proper freeze protection) or 0°F (limit set by design, cannot
be disabled). As an exception, this will not stop a chiller already running.
Start Inhibited by Low Ambient Temp
The chiller is inhibited from starting (and running) by an outdoor air ambient temperature
lower than a specified temperature - per user adjustable settings and can be disabled.
Start Inhibited by External Source The chiller is inhibited from starting (and running) by the "external stop" hardwired input.
Start Inhibited by BAS
The chiller is inhibited from starting (and running) by command from a Building Automation
System via the digital communication link (com 3 or com 5).
Waiting for BAS Communications
This is a transient mode - 15-min. max, and is only possible if the chiller is in the Auto -
Remote command mode. After a power up reset, it is necessary to wait for valid
communication from a Building Automation System (Tracer) to know whether to run or stay
inhibited. Either valid communication will be received from the Building Automation System
(e.g. Tracer), or a communication diagnostic ultimately will result. In the latter case the
chiller will revert to Local control.
Ice Building to Normal Transition
The chiller is inhibited from running for a brief period of time if it is commanded from active
ice building mode into normal cooling mode via the ice building hardwired input or Tracer.
This allows time for the external system load to "switchover" from an ice bank to the chilled
water loop, and provides for a controlled pull down of the loop's warmer temperature. This
mode is not seen if the ice making is automatically terminated on return brine temperature
per the mode below.
Ice Building is Complete
The chiller is inhibited from running as the Ice Building process has been normally
terminated on the return brine temperature. The chiller will not start unless the ice building
command (hardwired input or Building Automation System command) is removed or cycled.
Auto
The chiller is not currently running but can be expected to start at any moment given that
the proper conditions and interlocks are satisfied. Further information is provided by the
sub-mode:
Waiting For Evap Water Flow
The chiller will wait up to 4 minutes in this mode for evaporator water flow to be established
per the flow switch hardwired input.
Waiting for Need to Cool
The chiller will wait indefinitely in this mode, for an evaporator leaving water temperature
higher than the Chilled Water Setpoint plus the Differential to Start.
Starting
The chiller is going through the necessary steps to allow the lead circuit and lead compressor
to start.
No Sub Modes
Running
At least one circuit and one compressor on the chiller are currently running. Further
information is provided by the sub-mode:
Unit is Building Ice
The chiller is running in the Ice Building Mode, and either at or moving towards full capacity
available. Ice mode is terminated either with the removal of the ice mode command or with
the return brine temperature falling below the Ice Termination Setpoint.
Running - Limited
At least one circuit and one compressor on the chiller are currently running, but the operation
of the chiller as a whole is being actively limited by the controls.
Capacity Limited by
High Evap Water Temp
This mode will occur if both the OA temperature is above 40°F and the Evap Leaving Water
Temperature is above 75°F as is often the case in a high temperature pull-down. While in
this mode, no compressors will be allowed to load past their minimum load capacity step,
but it will not inhibit compressor staging. This mode is necessary to prevent nuisance trips
due to Compressor Overcurrent or High Pressure Cutout. Reasonable pull-down rates can
still be expected despite this limit.
Table 54. Chiller modes (continued)
Chiller Modes Description
Top Level Mode
Sub-modes
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