Trane TTA120D300AA Service Facts page 8

Sequence of Operation
ReliaTel™ Control Cooling Mode
For Zone Sensor Control
When the system switch is set to the COOL position and the zone temperature rises above the
cooling setpoint, the RTRM energizes the compressor contactor, provided the high and low
pressure and the discharge temperature limit controls are closed. When the compressor contacts
close, the compressor and the outdoor fan motor start to maintain the zone temperature to within
± 2°F of the sensor setpoint at the sensed location. On units with dual circuits, the second stage of
cooling is initiated as a result of the Proportional/Integral control algorithms calling for additional
cooling.
For Thermostat Control:
When the room thermostat system switch is positioned at COOL and the fan switch is at AUTO,
the RTRM energizes the compressor contactor, provided the high and low pressure and the
discharge temperature limit controls are closed. When the contacts of the compressor contactor
close, operation of the compressor and condenser fan begins. The evaporator fan contactor also
energizes on a call for cooling and initiates evaporator fan operation. On units with dual circuits,
the second stage of cooling is initiated as a result of the 2-stage thermostat calling for additional
cooling.
Note: Irregular unit operation may occur when the unit is controlled with a triac-switching
ReliaTel™ Control Evaporator Fan Operation
When the fan selection switch is set to the AUTO position, the RTRM energizes the evaporator fan
relay coil approximately 1 second after energizing the compressor contactor coil in the cooling
mode. In the heating mode, the RTRM energizes the evaporator fan relay coil approximately 1
second before energizing the electric heat contactors. The RTRM de-energizes the evaporator fan
relay coil approximately 60 seconds on dual compressor units and 80 seconds on single
compressor units after the cooling requirement has been satisfied to enhance unit efficiency. When
the heating cycle is terminated, the evaporator fan relay coil is de-energized at the same time as
the heater contactors. When the fan selection switch is set to the ON position, the RTRM keeps the
evaporator fan relay coil energized for continuous fan motor operation.
ReliaTel™ Control Heating Operation
Electric heat is factory disabled on all split system units with ReliaTel control (jumper placed
between J2-1 and J2-2 RTRM inputs). To configure the unit for electric heat, cut or remove the
jumper wire between J2-1 and J2-2 on the RTRM. All split system units with ReliaTel control are
also configured from the factory for only 1-stage of electric heat (jumper placed between J1-3 and
J1-6 RTRM inputs). To configure the unit for 2-stages of electric heat, cut or remove the jumper
placed between J1-3 and J1-6 RTRM inputs.
When the system switch is set to the HEAT position and heating is required, the RTRM energizes
the Heat 1 relay coil on the RTRM. When the Heat 1 relay contacts close, the first stage electric heat
contactor is energized. If the first stage of electric heat cannot satisfy the heating requirement, the
RTRM energizes the Heat 2 relay coil on the RTRM. When the Heat 2 relay contacts close, the second
stage electric heat contactor is energized. The first and second stages of heat are cycled "On" and
"Off" as required to maintain the zone.
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thermostat. Please review the approved thermostat vendor list for all recommended relay-
switching thermostats.
SS-SVF15A-EN