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CNT-SVX05A-EN
Binary inputs
Low temperature detection
The low temperature detection device can be automatically or manually reset.
However, you must manually reset the Tracer
™
AH.540 controller
Low
Temperature Detect
diagnostic to clear the diagnostic and restart the unit.
Low temperature detection protects the coils of hydronic units. A low
temperature detection device (freezestat) connected to binary input IN 7 detects
the low temperature. The Tracer AH.540 controller can protect the coil using
one binary input. When the controller detects the low temperature detection
signal, the controller generates a diagnostic which disables the fan, opens all
unit water or steam valves, and closes the outdoor air damper (when present).
Note:
Even if the low temperature detection device automatically resets when
the coil/heat exchanger temperature returns to a normal value, you must clear
the Low Temperature Detect diagnostic from the controller to restart the air
handling unit. See the Resetting Diagnostics section for instructions to clear
controller diagnostics.
Table 10 — Low temperature detection controller operation
Note 1:
When steam is the source of heat, the heat valve is cycled open and closed when the controller is shut down on
a
Low Temp Detect
latching diagnostic. Cycling the steam valve helps prevent excessive cabinet temperatures. See
Steam valve cycling
in the
Sequence of operation
section for further details.
Run/stop
This hardwired binary input IN 8 can be used for a variety of functions to shut
down the unit. The Tracer AH.540 controller systematically shuts down unit
operation and reports a
Unit Shutdown
diagnostic upon detecting a stop input.
For example, a condensate overflow sensor or a smoke detector can be
connected to the run/stop input to shut down unit operation.
The run/stop input creates a latching
Unit Shutdown
diagnostic. The run/stop
input must first be returned to the run condition and the diagnostic must be
reset in the controller before the unit is allowed to run.
Table 11 — Run/stop IN 8 binary input configuration
Diagnostic
Fan
operation
Cool
output
Heat output Face and
bypass
Outdoor air damper
operation
Low temperature
detection
Off
Open
Open
(Note 1)
Face
Closed
Configuration
Contact closed
Contact open
Not used
Run
Run
Normally closed
Run
Stop
Normally open
Stop
Run
