16
TTA-SVN03A-EN
Unit Start-Up
Once the unit is properly installed and
pre-start procedures are complete,
start the unit by turning the System
Switch on the indoor thermostat to
either HEAT, COOL or AUTO. The
system should operate normally.
CAUTION
Ensure the disconnect for the indoor
air handler is closed before operating
the system. Operating the indoor unit
without the indoor fan energized, can
cause unit trip-out on high pressure
control and/or liquid flood back to the
compressor.
Sequence of Operation
Electromechanical Controls
Unit Model Number Digits 9 and
10 = 00 or 0S
General
Operation of the system cooling (and
optional heating) cycles is controlled
by the position of the system switch
on the room thermostat. Once the
system switch is placed in either the
HEAT
or
COOL
position, unit
operation is automatic. The optional
automatic changeover thermostat,
when in the
AUTO
position,
automatically changes to heat or cool
with sufficient room temperature
change.
Evaporator Fan (Indoor Supply
Air)
The evaporator fan is controlled by an
ON/AUTO
switch on the room
thermostat. With the switch
positioned at
AUTO
and the system
operating in the cooling mode, fan
operation coincides with the cooling
run cycles. If the system is equipped
with heat and is operating in the
heating mode while the fan switch is
at
AUTO
, fan operation coincides with
the heating run cycles. When the fan
switch is positioned at
ON,
fan
operation is continuous.
Cooling Mode
With the disconnect switch in the
ON
position, current is supplied to the
compressor sump heater(s) and
control transformer. The sump
heater(s) supplies heat to the
compressor(s) during the
“Off”
cycle. The transformer steps down the
line voltage to 24V for the low voltage
control circuit. With the room
thermostat system switch is
positioned at
COOL
and the fan
switch is at
AUTO
, the compressor
contactor energizes on a call for
cooling. 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.
System Start Procedure
Electromechanical Controls