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140 RT-SVD03L-EN
TCI Comm 3/4
Discharge Air Sensing
Units connected to ICS systems have the ability to look
at discharge air temperature. Units using COMM3/4
only have the ability to see one point for discharge air
temperature and that is through the mixed air sensor
input on the ECA module labeled MAT. This input is
reported back to the ICS display graphics as SAS
(supply air sensor). The discharge air sensor is used for
supply air tempering with an ICS system or a
BAYSENS019* programmable zone sensor.
Systems using LonTalk ® and LCI have the ability to see
both mixed air and discharge air temperature.
The following discussion is focused only on units
utilizing COMM3/4 communications.
If an economizer is not installed, the discharge air
sensor option is required to monitor discharge air
temperature. The sensor must be used in conjunction
with the RTOM module (optional on 3 to 25 ton units).
The discharge sensor will be located in the discharge
opening of the unit.
3 to 25 Tons Units
If a unit has an economizer, in order to monitor true
discharge air temperature, the unit can use the mixed
air sensor, but it will have to be relocated to the
discharge of the unit. If the mixed air sensor is
relocated to the discharge of the unit, no further action
is required. The sensor will report back true discharge
temperature through the economizer module, and also
still function as the mixed air sensor for the economizer
operation. The discharge air sensor option is the
recommended method because it uses an averaging
tube to sense the air across the discharge opening. This
sensor will have to be wired back to the mixed air
sensor (MAT) input on the economizer module and
replaces the MAT sensor.
N No otte e:: If the unit has an economizer and the discharge
air sensor option is installed, then a 5.6K (1/4
watt) resistor must be installed on the OAT
terminals of the economizer actuator module
(ECA). This resistor will allow the economizer to
continue operation from the mixed air sensor.
The discharge air sensor will report true
discharge temperature to the RTOM, and in turn,
to the ICS panel via the TCI COMM3/4
communications. KIT08318 can be ordered for
the 5.6K resistor.
27.5 to 50 Tons Units
The discharge air sensor is standard on VAV units, but
is optional on CV units.
Service Note
Should there be a failure of either the mixed air sensor
or the discharge air sensor, the diagnostic will be
reported back as a supply air sensor failure. It will
require a visit to the job site to determine which sensor
has failed.