22
RT-SVX36G-EN
General Information
Freeze Avoidance
Freeze Avoidance is a feature which helps prevent freezing of hydronic heat coils and avoiding
nuisance hydronic heat freezestat trips. This is accomplished by opening inactive hydronic heat
valve(s) at low ambient temperatures.
Typically, when the unit is in a mode where the supply fan is off, the OA temperature is monitored.
If it falls below 45 ºF (5 degrees above the freezestat), the hydronic heat valve(s) are opened to the
Standby Freeze Avoidance Position. When the OA temperature rises above 47 ºF, occupied mode
is requested, or the supply fan is requested ON the hydronic heat valve(s) release to normal control.
When the supply fan is commanded on, the OA dampers will remain closed for one minute to
remove the heat from the hydronic heating coil. This prevents freezestat trips and falsely loading
the supply air temperature causing premature compressor operation. This function is disabled if
the Standby Freeze Avoidance Position is set to 0%.
Supply Air Temperature Low Limit
Uses the supply air temperature sensor input to modulate the economizer damper to minimum
position in the event the supply air temperature falls below the occupied heating setpoint
temperature.
Freezestat (4S12)
This is a binary input device used on units with Hydronic Heat. It is mounted in the heat section and
connected to the Heat Module (1U50). If the temperature of the air entering the heating coil falls
to 40°F, the normally open contacts on the freezestat closes signalling the Heat Module (1U50) and
the Rooftop Module (RTM) to:
•
Drive the Hydronic Heat Actuator (4U15) to the full open position.
•
Turn the supply fan “Off”.
•
Closes the outside air damper;
•
Turns “On” the SERVICE light at the Remote Panel.
•
Initiates a “Freezestat” diagnostic to the Human Interface.
High Duct Temp Thermostats (Optional 3S16, 3S17)
These are binary input devices used with a Trane Communication Interface Module (TCI). They
provide “high limit” shutdown of the unit and requires a manual reset. They are factory set to open
if the supply air temperature reaches 240°F, or the return air temperature reaches 135°F. Once
tripped, the thermostat can be reset by pressing the button located on the sensor once the air
temperature has decreased approximately 25°F below the cutout point.
Compressor Circuit Breakers (1CB8, 1CB9, 1CB10, 1CB11)
The Scroll Compressors are protected by circuit breakers for 208 - 230 volt units which interrupt the
power supply to the compressors if the current exceeds the breakers “must trip” value. For 460 -
575 volt units the Scroll compressors will be protected with Manual Motor protectors. During a
request for compressor operation, if the Compressor Module detects a problem outside of it's
normal parameters, it turns any operating compressor(s) on that circuit “Off”, locks out all
compressor operation for that circuit, and initiates a manual reset diagnostic.
Constant Volume (CV) Units
Zone Temperature - Cooling
Relies on input from a sensor located directly in the space, while a system is in the occupied
“Cooling” mode. It modulates the economizer (if equipped) and/or stages the mechanical cooling
“On and Off” as required to maintain the zone temperature to within the cooling setpoint
deadband.
