UNT-IOM-6
111
Terminal Unit
Control (TUC)
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 3-wire floating point), the valve(s) may not
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 105-106.
Table 46Continued. 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 3-wire floating point), the valve(s) may not
operate properly.
No Power to the TUC
The TUC requires a 24 VAC power for the unit to operate properly.
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 105-106.
