Trane LPC Install And Operation Instructions page 85

• Duct static pressure high limit (see
"Variable-air-volume supply fan
operation: Duct static pressure")
• Coil freeze protection
1. Face-and-bypass heating ("Face-and-
bypass damper operation")
2. Freeze avoidance (see "Freeze-
avoidance valve cycling")
3. Mixed-air temperature control (see
"Mixed-air temperature control")
4. Low-temperature detection (see
"IN7: Low-temperature detection or coil
defrost")
• Supply fan motor thermal protection
(see "Electric heat operation")
• Filter status (see "Filter status")
• Freeze avoidance (see "Freeze
avoidance")
Filter status
The controller filter status is based on the
supply fan cumulative run hours. The
controller compares the fan run time
against an adjustable fan run hours limit
(maintenance required setpoint time,
stored in the controller) and recommends
unit maintenance as required. The
Maintenance Required diagnostic is
informational only. Its state does not
affect unit operation.
Use the Rover service tool to edit the
Maintenance Required setpoint time.
When the setpoint limit is exceeded, the
controller generates a Maintenance
Required diagnostic. To disable the
diagnostic feature, set the maintenance
required setpoint time to zero.
You can use Rover service tool or Tracer
Summit to clear the Maintenance
Required diagnostic. When the diagnostic
is cleared, the controller resets the fan
run time to zero and resumes accumulat-
ing fan run hours.
Freeze avoidance
Freeze avoidance is used as low ambient
temperature protection and is only
initiated anytime 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 (1.67ºC) 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
LPC-SVX01C-EN
Operation
• Steam and hydronic heat 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 hydronic heating and
cooling coils from freezing when cold
outdoor air temperatures are present
and the supply fan is Off. For example,
the Tracer AH540/541 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
AH540/541 opens all water valves.
Overrides
The controller has the capability, whether
using space temperature control or
discharge air temperature control, to
override both analog and binary output
(typically for testing and commissioning)
through the Tracer Summit building
automation system or from the Rover
service tool. For more information about
the output overrides, refer to literature
for those products. In addition, AH540/541
override capability include:
• Manual output test
• Emergency override
• Water valve override
Manual output test
The controller includes a manual output
test function, which allows the user to
manually exercise the outputs in a
predefined sequence using the Test push
button (see "Performing a manual output
test"). You can also perform the manual
output test remotely using the Rover
service tool. The Rover service tool
Table O-SO-14. Emergency override commands
sequence of
operation
communications through the Comm5 link
to place the controller in service override
mode. From the Rover computer screen
you can step the controller through the
manual output test.
Emergency override
The Tracer AH540/541 controller can be
placed into emergency override by using
the communication variable
(nviEmergOverride). 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
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
Table O-SO-14.
Duct static pressure (when present) is
always controlled when the supply fan is
running. Freeze avoidance in emergency
override can force the heating and
cooling valves open.
Water valve override
To support water balancing, the controller
includes a communication variable
(nviValveOverride) that allows a user to
specify the desired state of all water
valves. The states supported are:
• Open all valves
• Close all valves
Unless the communicated variable is
refreshed within 10 hours, the override
ends and the valve operation reverts to
normal heating/cooling operation.
Use the Rover service tool to access this
feature.
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