Trane LO manual Tracer ZN.520, Valves Stay Closed, Probable Cause, Explanation

Tracer® ZN.520

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.

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