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Chapter 7 Troubleshooting
64 CNT-SVX07C-EN
Cycling fan operation/
continuous
The controller operates the fan continuously when in the occupied, occupied standby, or
occupied bypass mode. When the controller is in the unoccupied mode, the fan is cycled
between high speed and off with capacity.
Unoccupied operation Even if the controller is configured for continuous fan operation, the fan normally cycles
with capacity during unoccupied mode. While unoccupied, the fan cycles on or off with
heating/cooling to provide varying amounts of heating or cooling to the space.
Fan mode off If a local fan mode switch determines the fan operation, the off position controls the fan
off.
Requested mode off You can communicate a desired operating mode (such as off, heat, and cool) to the con-
troller. If off is communicated to the controller, the unit controls the fan off. There is no
heating or cooling.
Table 18. Valves remain closed
Probable cause Explanation
Unit wiring The wiring between the controller outputs and the valve(s) must be present and correct
for normal valve operation. Refer to applicable wiring diagram.
Failed end device The valves must be checked to ensure proper operation.
No power to the con-
troller
If the controller does not have power, the unit valve(s) will not operate. For the Tracer
ZN521 controller to operate normally, you must apply an input voltage of 24 Vac. If the
green LED is off continuously, the controller does not have sufficient power or has failed.
Power-up control-wait If power-up control-wait is enabled (non-zero time), the controller remains off until one of
two conditions occurs:
1) The controller exits power-up control-wait after it receives communicated information.
2) The controller exits power-up control-wait after the power-up control-wait time expires.
Diagnostic present Several diagnostics affect valve operation. For information about these diagnostics, see
Table 16 on page 59.
Normal operation The controller opens and closes the valves to meet the unit capacity requirements.
Unit configuration The controller must be properly configured based on the actual installed end devices and
application. If the unit configuration does not match the actual end device, the valves
may not work correctly.
Manual output test The controller includes a manual output test sequence you can use to verify output oper-
ation and associated output wiring. However, based on the current step in the test
sequence, the valves may not be open. Refer to the “Manual output test” on page 52.
Random start
observed
After power-up, the controller always observes a random start from 5 to 30 seconds. The
controller remains off until the random start time expires.
Requested mode off You can communicate a desired operating mode (such as off, heat, and cool) to the con-
troller. If off is communicated to the controller, the unit controls the fan off. There is no
heating or cooling.
Entering water
temperature
sampling logic
The controller includes entering water temperature sampling logic, which is automati-
cally initiated during 2-pipe and 4-pipe changeover if the entering water temperature is
either too cool or too hot for the desired heating or cooling. (See “AI1: Entering water
temperature” on page 17.)
Valve configuration Make sure the valves are correctly configured, using the Rover service tool, as normally
open or normally closed as dictated by the application.
Table 17. Fan does not energize (Continued)
Probable cause Explanation