Heat Pump Operation, 1 Or 2 Circuits; Defrost Operation; Electric Heat Operation; Dehumidification Operation - Trane Tracer UC400 Installation, Operation And Maintenance Manual

S S e e q q u u e e n n c c e e o o f f O O p p e e r r a a t t i i o o n n
pump unit when in cooling mode (using the reversing valve). Compressor(s) are held to a
minimum ON/OFF time of three (3) minutes and an inter-stage delay timer of three (3) minutes.
I I m m p p o o r r t t a a n n t t : : The UC400 Controller algorithms allow for opening of the economizer damper and

Heat Pump Operation, 1 or 2 Circuits

The UC400 Controller supports 1- or 2-stage heat pump for space temperature heating and
cooling. The heat pump unit may also include electric or hydronic auxiliary heating as backup
heating sources. In cooling mode, the controller commands the reversing valve to cooling mode
when the entering of cooling operation. It cycles the compressor(s) ON and OFF in order to
maintain the cooling space temperature setpoint. In heating mode, the controller commands the
reversing valve to heating mode and cycles the compressor(s) ON and OFF in order to maintain
the heating space temperature setpoint. In both heating and cooling modes, the compressor(s)
are held to a minimum ON/OFF time of three (3) minutes and an inter-stage delay timer of three
(3) minutes.
I I m m p p o o r r t t a a n n t t : : The UC400 Controller algorithms allow for opening of the economizer damper and

Defrost Operation

The UC400 Controller is equipped with a wired frost detection sensor BI4 for DX units. The
controller enters defrost mode when the sensor opens and shuts off the compressor(s) when
minimum ON times expire. During defrost, the fan and economizer damper continue to operate
and defrost the coil. Upon sensing completion of defrost, the controller immediately returns to
normal cooling control, clears the defrosting and compressor lockout status, and returns the
diagnostic binary point to NORMAL.
I I m m p p o o r r t t a a n n t t : : The minimum OFF time for DX compressors is still obeyed, so the compressor may

Electric Heat Operation

The UC400 Controller supports both SCR (modulating) and 1– or 2–staged electric heat. SCR heat
is only a field-installed option. If the controller is configured with staged electric heat, the electric
heating circuit(s) cycle ON and OFF to maintain the desired space temperature at the active
heating setpoint. If the controller is configured with SCR (modulating) electric heat, the unit
sends a 0 to 10 Volt DC signal to adjust SCR capacity in order to maintain the desired space
temperature. In both staged and modulating electric heat applications, the simultaneous use of
electric and hydronic heat is not supported. The UC400 Controller operates electric heat only
when hot water is not available (for example, in a changeover unit). In addition, the controller
runs the supply fan for 30 seconds after electric heat is turned OFF in order to dissipate heat from
the unit.
N N o o t t e e : : This delay does not apply to steam or hydronic heating.
Factory-configured electric heat units have built-in mechanical protections to prevent
dangerously high discharge air temperatures.

Dehumidification Operation

The UC400 Controller supports space dehumidification when:
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running the compressors simultaneously without tripping the frost sensor. The
controller supports one stage of direct expansion (DX) compressor operation for only
cooling.
running the compressors simultaneously without tripping the frost sensor. The
controller supports both 1-stage and 2–stage electric heat. Electric heat is cycled ON
and OFF to maintain the discharge air temperature at the active heating setpoint.
Two-pipe changeover units with electric heat use only electric heat when hot water is
not available. The use of both electric and hydronic heat is not supported.
not turn ON immediately when the defrost condition ends.
Mechanical (DX or hydronic) cooling is available.
The heating capacity is located in the reheat position.
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