Terminal Unit
Control (TUC)
Table 45—Continued. Fan Outputs not Energizing
Probable Cause | Explanation |
No power to the TUC Autocycle test
The TUC requires 24 VAC power for the unit to operate properly.
The controller includes an auto cycle test sequence that verifies analog and binary output operation and associated output wiring. However, based on the current stage in the test sequence, supply fan may be off. Refer to the “Autocycle Test” section on page 71.
Wiring | The wiring between the controller outputs and the fan relays and |
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| contacts must be present and correct for normal fan operation. |
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| Refer to the typical unit wiring diagrams on pages |
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| Table 46. Valves Closed |
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| Probable Cause | Explanation |
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| Normal operation | The valves open and close to meet unit capacity requirements. |
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| unit disabled | · The TUC may be disabled via the shutdown mode on a Tracer® |
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| system or if BIP1 is configured as external interlock. |
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| · During the stop modes, the valves remain closed unless freeze |
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| avoidance is enabled and the fresh air temperature falls |
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| below the freeze avoidance setpoint (configurable). |
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| · If the fresh air temperature falls below the freeze avoidance |
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| setpoint, the valves open. The TUC enables freeze avoidance |
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| whenever the freeze avoidance setpoint is not zero. |
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| Override present | The valves may be overridden to the closed position by either the |
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| Tracer® system or by Everyware™ software. Whenever any override |
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| is active, the TUC drives the valves closed unless they are concur- |
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| rently overridden open. |
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| Latching diagnostic presen | A specific list of diagnostics effects valve operation. For more |
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| information, see the “Diagnostics” section on page 73. Latching |
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| diagnostics require a manual reset to restore normal unit operation. |
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| Autocycle test | The controller includes an autocycle test sequence that verifies |
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| analog and binary output operation and associated output wiring. |
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| However, based on the current stage in the test sequence, the |
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| valve(s) may be closed. Refer to the “Human Interface” section on |
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| page 62. |
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| Maximum heating/cooling | The Tracer® may limit the maximum heating/cooling capacity of the |
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| capacity of zero | TUC from zero to 100%. When the maximum cooling capacity is |
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| zero, the cooling valve remains closed. When the maximum heating |
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| capacity is zero, the heating valve remains closed. |
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110 |
