Terminal Unit
Control (TUC)
Table 46—Continued. Valves Closed
Probable Cause | Explanation |
Unit Configuration | The TUC cannot control any valve outputs if the unit is configured |
| for no valves. Also, if the valve type is incorrectly configured (on/off, |
| modulating analog, or |
| operate properly. |
No Power to the TUC Wiring
The TUC requires a 24 VAC power for the unit to operate properly.
The wiring between the controller outputs and the valve(s) must be present and correct for normal valve operation. Refer to the typical unit wiring diagrams on pages
Table 47. Valves Open
Probable Cause | Explanation |
Normal Operation | The valves open and close to meet unit capacity requirements. |
Override Present | The valves may be overridden to the open position by either the |
| Tracer® system or by Everyware™ software. Whenever any |
| override is active, the TUC drives the valves closed unless they are |
| concurrently overridden open. |
Autocycle Test | The controller includes an autocycle test sequence that verifies |
| analog and binary output operation and associated output wiring. |
| However, based on the current stage in the test sequence, the |
| valve(s) may be open. Refer to the “Autocycle Test” section on |
| page 71. |
Unit Configuration | The TUC cannot control any valve outputs if the unit is configured |
| for no valves. Also, if the valve type is incorrectly configured (on/off, |
| modulating analog, or |
| operate properly. |
Freeze Avoidance | When freeze avoidance is enabled (active only during stop modes) |
| the TUC controls the valve(s) open whenever the fresh air tempera- |
| ture is less than the freeze avoidance setpoint (configurable). If the |
| freeze avoidance setpoint is zero, this feature is disabled. |
Wiring | The wiring between the controller outputs and the valve(s) must be |
| present and correct for normal valve operation. Refer to the typical |
| unit wiring diagrams on pages |
111 |
