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Terminal Unit
Control (TUC)
112 UNT-IOM-6
Table 48. Electric Heat Not Operating
Probable Cause Explanation
Normal Operation The controller cycles electric heat on and off to meet the unit
capacity requirements.
Unit Disabled The TUC may be disabled via the shutdown mode on a Tracer
®
system or if BIP1 is configured as external interlock.
Electric Heat Control: Disable The electric heat may be disabled with the Tracer
®
system. To
enable the electric heat, the TUC electric heat control must be set
to the auto postion.
Maximum heating capacity of zero The Tracer
®
may limit the maximum heating/cooling capacity of the
TUC from zero to 100%. When the maximum heating capacity is
zero, the electric heat is disabled.
Latching Diagnostic Present A specific list of diagnostics affects electric heat 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, based on the current stage in the test sequence, the
electric heat may be disabled. Refer to the Autocycle Test
section on page 71.
Unit Configuration The TUC cannot control the electric heat output if the unit is config-
ured for no electric heat. Also, if the electric heat type is incorrectly
configured (1 or 2 stage), the electric heat may not operate prop-
erly.
No Power to the TUC The TUC requires 24 VAC power for the unit to operate properly.
Wiring The wiring between the controller outputs and the electric heat must
be present and correct for normal electric heat operation. Refer to
the typical unit wiring diagrams on pages 105-106.