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Operation
57RT-SVX20A-E4
Low Ambient Operation
During low ambient operation,
outside air temperature below 13ºC,
the RTRM will cycle the compressor
and outdoor fan motor "Off" for
approximately three minutes after
every 10 minutes of accumulated
compressor run time. The supply
fan motor (IDM) will continue to
operate during this evaporator
defrost cycle (EDC) and the
compressor and outdoor fan will
return to normal operation once the
defrost cycle has terminated and
the compressor "Off" time delay has
been satisfied.
Cooling with an
Economizer
The economizer is utilized to control
the zone temperature providing the
outside air conditions are suitable.
Outside air is drawn into the unit
through modulating dampers. When
cooling is required and economizing
is possible, the RTRM sends the
cooling request to the unit
economizer actuator (ECA) to open
the economizer damper. The RTRM
tries to cool the zone utilizing the
economizer to slightly below the
zone temperature setpoint. If the
mixed air sensor (MAS) senses that
the mixed air temperature is below
53ºF, the damper modulates toward
the closed position. If the zone
temperature continues to rise above
the zone temperature setpoint
controlband and the economizer
damper is full open, the RTRM
energizes the compressor contactor
(CC1). If the zone temperature
continues to rise above the zone
temperature setpoint controlband
and the economizer damper is fully
open, the RTRM energizes the
compressor contactor (CC2).
The ECA continues to modulate the
economizer damper open/closed to
keep the mixed air temperature that
is calculated by the RTRM.
If economizing is not possible, the
ECA drives the damper to the
minimum position setpoint when
the supply fan relay (F) is energized
and allows mechanical cooling
operation. When the unit is
equipped with the optional fan
failure switch, wired between
terminals J7-5 and J7-6 on the
RTOM, the RTRM will stop all
cooling functions and produce an
analog output if the fan failure
switch (FFS) does not open within
40 seconds after a request for fan
operation. When the system is
connected to a remote panel, the
"SERVICE" LED will flash when this
failure occurs.