Tracer
®
ZN.520
86
UNT-IOM-6
Table 36. Valves Stay Closed
Probable Cause
Explanation
Requested mode off
You can communicate a desired operating mode (such as off, heat, and
cool) to the controller. When off is communicated to the controller, the
unit controls the fan off. There is no heating or cooling (valves are
closed).
Power up control wait
When power up control wait is enabled (non-zero time), the controller
remains off until one of two conditions occurs:The controller exits power
up control wait once it receives communicated information.The controller
exits power up control wait once the power up control wait time expires.
Manual output test
The controller includes a manual output test sequence you can use to
verify output operation and associated output wiring. However, based on
the current step in the test sequence, the valve(s) may not be open.
Refer to the Manual Output Test section.
Fan mode off
When a local fan mode switch (provided on the Trane zone sensor)
determines the fan operation, the off position controls the unit off and
valves to close.
Sampling logic
The controller includes entering water temperature sampling logic which
is automatically invoked during 2-pipe and 4-pipe changeover when the
entering water temperature is either too cool or too hot for the desired
heating or cooling.Refer to the Entering Water Temperature Sampling
section.
Diagnostic present
A specific list of diagnostic affects valve operation. For more information,
see the Diagnostics section.
Unit configuration
The controller must be properly configured based on the actual installed
end devices and application. When the unit configuration does not match
the actual end devices, the valves may not work correctly.Example: A 2-
pipe heat/cool changeover unit will not cool if the entering water tempera
ture is too warm for cooling or if the entering water sensor is not present.
The unit will not heat if the entering water temperature is too cool for
heating.
Unit wiring
The wiring between the controller outputs and the valve(s) must be
present and correct for normal valve operation.
Random start observed After power up, the controller always observes a random start from 0 to
25 seconds. The controller remains off until the random start time
expires.
