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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 46—Continued. Valves Closed