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Operation
RT-SVX20A-E450
Unoccupied mode
If the thermostat being used is
programmable, it will have its own
strategy for unoccupied mode and
will control the unit directly. If a
mechanical thermostat is being
used, a field applied time clock with
relay contacts connected to J6-11
and J6-12 can initiate an
unoccupied mode as follows:
• Contacts open: Normal occupied
operation.
• Contacts closed: Unoccupied
operation as follows - Fan in
auto mode regardless of fan
switch position. Economizer
closes except while economizing
regardless of minimum position
setting.
Cooling/Economizer Operation
If unit does not have an economizer,
the Cool/Econ Stage 1 and Stage 2
will call directly for mechanical
cooling (compressor) stages. If the
unit has an economizer, the
Cool/Econ stages will function as
shown in Table 46.
Table 46 - Cooling/Economizer Operation with Thermostat
Notes:
40 t
o 50 ton CV only
This unit has 3 stages of cooling if using a zone sensor. If using a conventional thermostat it has 2 stages as
follows:
Y1 = 1st stage
Y1 + Y2 = 3rd stage
VAV
Thermostat inputs are ignored on VAV units.
OK to
Economize?
Thermostat
Y1
Thermostat
Y2
Call for Economizer
Cooling
Compressor Staging
Request
No On Off Inactive Compressor Output 1
No Off On Inactive Compressor Output 2
No On On Inactive
Compressor
Outputs 1 & 2
Ye s On Off Active Off
Ye s Off On Active Compressor off
Ye s On On Active Compessor
Setting the economizer or
0-50% motorized hood
(option)
The ECA board is mounted on the
damper actuator. To access the ECA
board on economizers:
• Remove the filter access panel of
the unit.
• The electrical power must be
disconnected to set the
minimum position and check the
economizer.
• Disconnect the power supply,
put the thermostat fan selector
to "ON" and the "HEAT/COOL"
selector to "OFF". This puts the
damper in the minimum
ventilation position.
• To set the required minimum
ventilation air position, turn the
dial on the ECA clockwise to
increase ventilation, or anti-
clockwise to decrease ventilation.
The damper will open at this
setting whenever the fan circuit
is powered up (see Figure 25).
• When the arrow on the dial's
adjustment screw is pointing to
8 o'clock, the minimum position
is roughly 0%. When the dial is
pointing to 12 o'clock it is
roughly 25%, and when the dial
is pointing to 4 o'clock it is
roughly 50% (see figure 25).