CNT-SVX05A-EN
53
Sequence of operation
initiated when the supply fan is off. The controller enters the freeze avoidance
mode when the outdoor air temperature is below the freeze avoidance setpoint
(configurable). The controller disables freeze avoidance when the outdoor air
temperature rises 3
°
F above the freeze avoidance setpoint. When the controller
is in freeze avoidance mode:
• all water valves are driven open to allow water to flow through the coil
• steam valves are cycled open and closed to prevent excessive cabinet
temperatures
• supply fan is off
• face and bypass damper (when present) is at full bypass
• freeze avoidance protects the air handling unit's hydronic heating and cooling
coils from freezing when cold outdoor air temperatures are present and the
supply fan is off.
Example:
The Tracer AH.540 is not able to run the air handling unit because the
run/stop input is set to stop (supply fan is off). If the outdoor air temperature is
below the freeze avoidance setpoint, the Tracer AH.540 opens all water valves.
Tracer Summit
™
and Rover
™
output overrides
The controller includes the capability to override both analog and binary outputs
(typically for test and commissioning) through Trane's Tracer Summit building
automation system or from Rover service tool. For more information on the
output overrides, refer to the product-specific literature for the building
automation system and the service tool.
The controller includes a Manual Output Test function which allows the user to
manually exercise the outputs in a predefined sequence. For more information,
refer to the
Manual output test
section.
Service override mode
The controller includes a Manual Output Test function which allows the user to
manually exercise the outputs in a predefined sequence from the Test push
button. The service override mode allows you to step through the Manual Output
Test remotely via Rover.
The Rover service tool communicates through the Comm5 link to place the
Tracer
™
AH.540 in service override mode. From the Rover computer screen you
can step the Tracer AH.540 controller through Manual Output Test sequence.
For more information, refer to the
Manual output test
section.
Emergency override
The Tracer AH.540 controller can be placed into emergency override via the
communication link. Emergency override allows a building automation system
such as Trane Tracer Summit to pressurize, depressurize, or purge the air from a
building space. It can also be used to shut down the controller’s operation of the
unit.
The emergency override command influences the controller's supply fan,
outdoor air damper, and exhaust fan to create the desired condition, as shown
in the following table.
Table 30 — Emergency override commands
Command
Supply fan
Outdoor air damper
Exhaust fan
Pressurize
On
Open
Off
Depressurize
Off
Close
On
Purge
On
Open
On
Shutdown
Off
Close
Off
