Sequence of operation
CNT-SVX04A-EN
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Water valve override
For supporting water balancing, the controller includes a communication
variable (nviValveOverride) that allows a user to specify the desired state of all
water valves. The only values supported are:
■ Open all valves
■ Close all valves
To maintain the controller in valve override, this variable must be rewritten at
least once every two hours. The controller resets itself if the variable is not
refreshed within two hours or any other value except open or closed is written
to it.
Rover or another communicating device is required to access this feature.
Fan status
The status of the fan is reported based on the state of the binary output(s)
dedicated to fan control. The fan status is reported as High, Medium, or Low
whenever the corresponding binary output is directed on. In all configurations,
the fan status is reported as Off when none of the fan outputs is energized.
The Tracer ZN.520 zone controller can be connected to a fan status switch
(when present on binary input 4) that provides a diagnostic for belt-drive units
or direct-drive units as needed. The fan status switch provides feedback to the
controller that the fan is in operation when the fan binary outputs are energized.
If the controller energizes a fan output for one full minute and the fan status
switch indicates no fan operation, the controller performs a unit shutdown and
generates a Low AirFlow—Fan Failure diagnostic. The controller also generates
a Low AirFlow—Fan Failure diagnostic if the fan status switch indicates no fan
operation for one minute after the fan has been operating normally. The fan
condition and the diagnostic must be cleared before the unit is allowed to
operate. If a diagnostic reset is sent to the controller and the fan condition still
exists, the controller attempts to run the fan for one minute before generating
another diagnostic and performing a unit shutdown.
Binary input 4 (BI4) is in the closed position when the fan is in operation and is
in the open position when fan operation has stopped.
Filter status
The controller’s filter status is based on the unit fan’s 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.
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