Trane ReliaTel - Discharge Air Sensing with TCI Comm3;4; 3-25 Ton Units; 27.5-50 Tons Units

11 8 RT-SVD03G-EN
Discharge Air Sensing with TCI Comm3/4
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-
25 tons units). The discharge sensor will be located in the discharge opening of the unit.
3-25 Ton 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.
Note: 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.
27.5-50 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.