Constant Volume (Cv), Single Zone Variable Air Volume (Szvav) & Variable Air Volume (Vav) Sensors And Controls - Trane IntelliPak SAHL Series Installation, Operation And Maintenance Manual

General Information
Constant Volume (CV), Single Zone Variable Air Volume (SZVAV) &
Variable Air Volume (VAV) Sensors and Controls
Supply Air Temperature Sensor (3RT9)
This an analog input device monitors the supply air temperature for; supply air temperature control
(used with discharge temperature control), supply air temperature reset (used with discharge
temperature control), supply air temperature low limiting (used with discharge temperature
control), supply air tempering. It is mounted in the supply air discharge section of the unit and is
connected to the RTM (1U48).
Return Air Temperature Sensor (3RT6)
This analog input device is used with a return humidity sensor when the comparative enthalpy
option is ordered. It monitors the return air temperature and compares it to the outdoor
temperature to establish 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).
Entering Evaporator Temperature Sensor (3RT28 and 3RT29)
This analog input device is used with the Leaving Evaporator Temp sensor to provide Low Charge
Protection of the refrigerant systems. The difference in these two temperatures will be monitored
during compressor operation and compressor circuits will be shut down if this difference exceeds
a Human Interface selectable setpoint value.
Leaving Evaporator Temperature Sensor (3RT14 and 3RT15)
An analog input device used to monitor 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 MCM. 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)
This binary input device 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/Return Airflow Proving Switches (3S68 and 3S69)
3S68 is a binary input device used to signal the RTM when the supply fan is operating. It is located
in the supply fan section of the unit and is connected to the RTM (1U48). During a request for fan
operation, 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 operation is
turned "Off" and locked out, exhaust dampers (if equipped) are "closed" , economizer dampers (if
equipped) are "closed" , and a manual reset diagnostic is initiated.
3S69 is a binary input device used on all rooftop units equipped with an exhaust/return fan. It is
located in the exhaust/return fan section of the unit and is connected to the RTM (1U48). During a
request for fan operation, if the differential switch is detected to be open for 40 consecutive
seconds, the economizer is closed to the minimum position setpoint, the request for exhaust/return
fan operation is turned "Off" and locked out, and a manual reset diagnostic is initiated. The fan
failure lockout can be reset; at the Human Interface located in the unit's control panel, by Tracer,
or by cycling the control power to the RTM (1S70 Off/On).
18 RT-SVX36G-EN