Ambient Sensing; Blower Control; Economizer Mode - EngA C-TRAC3 Installation, Operation And Maintenance Manual

A
C-TRAC3

AMBIENT SENSING

The C-TRAC3 constantly monitors the ambient temperature using an Engineered Air TE6000EA3 sensor. On
initial start up the C-TRAC3 pre-determines which mode to start in: heating, cooling, or economizer. The
load requirements, ambient temperature and digital inputs determine which mode the C-TRAC3 can start
in. Note that some applications will involve dual modes, such as dehumidification and multi-zone
equipment.
The C-TRAC3 must have an ambient sensor installed to operate, or it will lockout on 'open sensor' failure.

BLOWER CONTROL

When 24Vac is applied to terminal FS the C-TRAC3 is considered to be in occupied mode. After a time
delay, that allows the damper actuators to respond, the blower(s) will be enabled by closing the output
contact between terminals C and SA. The time delay is variable depending on the equipment and the
function.
Control of occupied and unoccupied time may be accomplished with an EMS controller. If used, and
enabled by the SMC programming software, the 24Vac input into terminal K is not required.
Fan start timing will vary depending on the unit configuration. Make up air equipment has a base delay
time of 90 seconds, while equipment with mixing dampers have a 10 second base delay time. Additionally,
there may be delays for morning warm up, cool down, and pump down, which may vary depending on the
ambient and discharge air temperature. Always refer to the unit function for specific application time
values. The fan delay off time can vary from 10s to 2.5 minutes.

ECONOMIZER MODE

When in economizer mode the C-TRAC3 will mix the warm return air with the cool outside air to try and
achieve the required discharge SPC. The C-TRAC3 will modulate the mixing dampers (return, outside and if
equipped, exhaust) from fully open to the minimum position setting (expressed as a percentage of outside
air).
The C-TRAC3 has 2 independent outputs for damper control. One is a 24Vac output from terminal DM for
on/off control or a 2 position damper actuator. The other is a modulating Vdc output from terminal ED for
modulating (economizer) actuator control. Flat mixing boxes are set to output a 0-7Vdc range, while angle
mixing boxes use a 0-10Vdc range.
The C-TRAC3 will drive the actuator to minimum position when in heating mode. Optionally, the
C-TRAC3 can be programmed to either drive the damper actuator to minimum position when in cooling
mode or continue to modulate to 100% outside air. If set to modulate, the dampers will decrease the
amount of outside air as the mechanical cooling is enabled to ensure that there is sufficient startup load to
avoid damaging the compressor. Once the compressor has started, the dampers will slowly modulate
open, as required.
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