Start Up
RT-SVX50F-EN
25
When there is a call for Cool 2, the second compressor is
energized and the Supply Fan will switch to High Speed.
The unit will stage down compressors for cooling in
reverse order that they were staged and the supply fan will
follow the unit mode transitions. Once it is determined
through normal cooling control that the second
compressor is no longer necessary to meet cooling
demand, the second compressor will be staged back and
the supply fan will switch to Low Speed until the unit
stages all cooling off or receives a call for Cool 2 again.
Once the Supply Fan is no longer requested ON after a
Cooling call is cleared, the Supply Fan will remain
energized at Low Speed for 60 seconds as on traditional
units.
If the economizer is enabled and is being utilized as the
first stage of cooling (Y1 active), if the unit receives a Y2
request, the unit will energize the first compressor and will
switch the supply fan to high speed until the Y2 request is
cleared.
Economizer Minimum Position Handling for 2-
Speed Fan
Due to the low and high speeds of the indoor fan, when the
unit is in Fan Only, Cool 1, or Economizer Only and the
indoor fan is at low speed, the unit will not be bringing in
as much fresh air as normal. By setting a higher minimum
damper position this problem could be solved, but that
would mean more fresh air than may be desired when the
supply fan is at high speed. To overcome these situations,
the control will require the setting of two economizer
minimum positions to be used when the fan is at low and
high speed to compensate for the lower amount of fresh
air at lower fan speeds and the potential for more fresh air
than desired at higher fan speeds. These minimum
positions will be obtained from the Bldg Design Min
Position and DCV Min Position pots on the RTEM-EM. The
economizer minimum position that will be utilized while
the supply fan is at low speed will be set with the DCV Min
Position pot with a range of 0-100% and the minimum
position that will be utilized while the supply fan is at high
speed will be set with the Building Design Min Position pot
with a range of 0-50%. If the Building Design Min Position
is set to be higher than the DCV Min Position, the setpoints
will be capped at the DCV Min Position and the setpoint for
the min position at low and high fan speed will be the DCV
Min Position.
Phase Monitor
The phase monitor is a 3 phase line monitor module that
protects against phase loss, phase reversal and phase
unbalance. It is intended to protect compressors from
reverse rotation. It has an operating input voltage range of
190-600 VAC, and LED indicators for ON and FAULT. There
are no field adjustments and the module will automatically
reset from a fault condition.
Low Pressure Cutout
The low pressure cutouts are wired in series with the high
pressure cutouts and the temperature discharge limits. If
this circuit is open before a compressor is started, the
compressor in that circuit will not be allowed to operate.
Anytime this circuit is opened, the compressor in that
circuit is turned off immediately.
High Pressure Cutout and Temperature
Discharge Limit
The high pressure controls and temperature discharge
limit are wired in series between the compressor outputs
on the LTB and the compressor contactors. If the high
pressure safety or temperature discharge limit opens, the
compressor on the affected circuit is turned off.
Locking Safety Device with Compressor Anti
Short Cycle Timer
This device monitors compressor safety switch trips to
prevent short cycling, protecting the compressor. A
manual reset is required after a fourth safety switch trip.
Coil Frost Protection
The Frostat™ control monitors the evaporator coil
temperature to prevent the evaporator from freezing due
to low operating temperatures whenever there is a
demand for cooling. When a open circuit has occurred, the
Frostat opens the 24VAC ground and opens all of the
cooling contactors.
Heating Operation
Standard unit operation for heating will continue on units
equipped with a two-speed indoor fan. During heat mode,
all units configured with staged electric or gas heat will
heat the supply air and space as normal utilizing full speed
indoor fan.
Emergency Stop
This input de-energizes the 24VAC output from the phase
monitor and can be activated by opening a field supplied
device connected to the LTB.