Trane RT-SVX10C-EN General Information Continued, Input Devices & System Functions, Unit

Ventilation Control Module (VCM - Design special option only)

The Ventilation Control Module (VCM) is located in the filter section of the unit and is linked to the unit's UCM network. Using a "velocity pressure" sensing ring located in the fresh air section, allows the VCM to monitor and control the quan- tity of fresh air entering the unit to a minimum airflow set- point.

An optional temperature sensor can be connected to the VCM which enables it to control a field installed fresh air preheater.

An optional CO2 sensor can be connected to the VCM to control CO2 reset. The reset function adjust the minimum CFM upward as the CO2 concentrations increase. The maximum effective (reset) setpoint value for fresh air enter- ing the unit is limited to the systems operating CFM. The following table lists the Minimum Outside Air CFM vs Input Voltage.

Minimum Outside Air Setpoint w/VCM Module & TraqTM Sensing

Unit	Input Volts	CFM
20 & 25 Ton	0.5 - 4.5 vdc	0 - 14000
30 Ton	0.5 - 4.5 vdc	0 - 17000
40 Ton	0.5 - 4.5 vdc	0 - 22000
50 & 55 Ton	0.5 - 4.5 vdc	0 - 28000
60 thru 75 Ton	0.5 - 4.5 vdc	0 - 33000
90 thru 130 Ton	0.5 - 4.5 vdc	0 - 46000

The velocity pressure transducer/solenoid assembly is illus- trated below. Refer to the "TraqTM Sensor Sequence of Op- eration" section for VCM operation.

Velocity Pressure Transducer/Solenoid Assembly

Generic Building Automation System Module (GBAS - Optional 1U51 used with non-Trane building control systems)

The Generic Building Automation System (GBAS) module allows a non-Trane building control system to communicate with the rooftop unit and accepts external setpoints in form of analog inputs for cooling, heating, supply air pressure, and a binary Input for demand limit. Refer to the "Field In- stalled Control Wiring" section for the input wiring to the GBAS module and the various desired setpoints with the corresponding DC voltage inputs for both VAV and CV ap- plications.

General Information (Continued)

For complete application details of the module, refer to En- gineering Bulletin RT-EB-109.

Input Devices & System Functions

The descriptions of the following basic Input Devices used within the UCM network are to acquaint the operator with their function as they interface with the various modules. Refer to the unit's electrical schematic for the specific mod- ule connections.

Constant Volume & Variable Air Volume Units

Supply Air Temperature Sensor (3RT9)

Is an analog input device used with CV & VAV applications. It monitors the supply air temperature for; supply air tem- perature control (VAV), supply air temperature reset (VAV), supply air temperature low limiting (CV), supply air temper- ing (CV/VAV). It is mounted in the supply air discharge sec- tion of the unit and is connected to the RTM (1U48).

Return Air Temperature Sensor (3RT6)

Is an analog input device used with a return humidity sen- sor on CV & VAV applications when the comparative en- thalpy option is ordered. It monitors the return air tempera- ture and compares it to the outdoor temperature to estab- lish which temperature is best suited to maintain the cooling requirements. It is mounted in the return air section and is connected to the ECEM (1U52).

Evaporator Temperature Sensor (3RT14 and 3RT15)

Is an analog input device used with CV & VAV applications. It monitors the refrigerant temperature inside the evaporator coil to prevent coil freezing. It is attached to the suction line near the evaporator coil and is connected to the SCM/MCM (1U49). It is factory set for 30 F and has an adjustable range of 25 F to 35 F. The compressors are staged "Off" as necessary to prevent icing. After the last compressor stage has been turned "Off", the compressors will be allowed to restart once the evaporator temperature rises 10 F above the "coil frost cutout temperature" and the minimum three minute "Off" time has elapsed.

Filter Switch (3S21)

Is a binary input device used on CV & VAV applications. It measures the pressure differential across the unit filters. It is mounted in the filter section and is connected to the RTM (1U48). A diagnostic SERVICE signal is sent to the remote panel if the pressure differential across the filters is at least 0.5" w.c.. The contacts will automatically open when the pressure differential across the filters decrease to 0.4" w.c.. The switch differential can be field adjusted between 0.17" w.c. to 5.0" w.c. ± 0.05" w.c..

Supply and Exhaust Airflow Proving Switches (3S68 and 3S69)

3S68 is a binary input device used on CV & VAV applica- tions to signal the RTM when the supply fan is operating. It is located in the supply fan section of the unit and is con- nected to the RTM (1U48). During a request for fan opera- tion, if the differential switch is detected to be open for 40 consecutive seconds; compressor operation is turned "Off", heat operation is turned "Off", the request for supply fan op- eration is turned "Off" and locked out, IGV's (if equipped) are "closed", exhaust dampers (if equipped) are "closed", economizer dampers (if equipped) are "closed", and a manual reset diagnostic is initiated.

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