Terminal Unit

Control (TUC)

Table 49. Fresh Air Damper Closed

Probable Cause

Explanation

Normal Operation

· The two-position fresh air damper opens under normal unit operation

 

during occupied mode and closes during unoccupied mode.

 

· Modulating analog and 3-wire floating point economizers open to

 

the minimum position (configurable) when the unit is occupied and

 

modulate to meet unit capacity requirements.

 

· If the minimum damper position is zero, the damper may close for

 

extended periods. During the unoccupied mode, the normal fresh

 

air damper position is closed.

Unit Disabled

·Tracer® may disable via the shutdown mode on a system or if

 

BIP1 is configured as external interlock.

 

· During the stop modes, the fresh air damper remains closed.

Override Present

The fresh air damper may be overridden closed by either the

 

Tracer® system or by Everyware™ software. Whenever any override

 

is active, the TUC drives the fresh air damper closed, unless the

 

damper is concurrently overridden open.

Latching Diagnostic Present

Specific diagnostics affect damper operation. For more information,

 

see the “Diagnostics” section on page 73. Latching diagnostics

 

require a manual reset to restore normal unit operation.

Autocycle Test

The controller includes an autocycle test sequence that verifies

 

analog and binary output operation and associated output

 

wiring. However, the current test sequence stage may require the

 

damper to close. Refer to the “Autocycle Test” section on page 71.

Unit Configuration

The TUC cannot control fresh air damper outputs if the unit is config-

 

ured for no fresh air damper. Also, if the fresh air damper is incor-

 

rectly configured (on/off, modulating analog, or 3-wire floating point),

 

it may not operate properly.

Warm-Up Mode

When the occupied preheat damper position is closed, the unit

 

closes the fresh air damper whenever the zone temperature falls

 

3° F or more below the active heating setpoint. The fresh air damper

 

remains closed until the zone temperature is within 2° F of the

 

active heating setpoint.

Local Fan Switch: Off

Using the local fan mode switch to determine the fan operation, the

 

off position will control the unit fan off close the fresh air damper.

No Power to the TUC

The TUC requires 24 VAC power for proper operation. Wiring

 

The wiring between the controller outputs and the fresh air damper

 

must be present and correct for normal damper operation. Refer to

 

typical unit wiring diagrams on pages 105-106.

Motion Detection Feature

If motion detection is enabled and no motion is detected in the

 

space (by a motion sensor wired to BIP2), the TUC will

 

apply an alternate fresh air minimum damper position.

UNT-IOM-6

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Trane LO manual Fresh Air Damper Closed Probable Cause Explanation
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