Low Ambient Compressor Lockout
Utilizes an analog input device for CV & VAV applications. When the system is configured for low ambient compressor lockout, the compressors are not allowed to operate if the temperature of the outside air falls below the lockout set- point. When the temperature rises 5 F above the lockout setpoint, the compressors are allowed to operate. The set- point for units without the low ambient option is 50 F. For units with the low ambient option, the setpoint is 0 F. The setpoints are adjustable at the Human Interface inside the unit control panel.
Space Pressure Transducer (3U62)
Is an analog input device used on CV & VAV applications with the Statitrac option. It modulates the exhaust dampers to keep the space pressure within the building to a cus- tomer designated controlband. It is mounted in the filter section just above the exhaust damper actuator and is con- nected to the ECEM (1U52). Field supplied pneumatic tub- ing must be connected between the space being controlled and the transducer assembly.
Transducer Voltage Output vs Pressure Input
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| 0.0 | 0.5 | 1.0 | 1.5 | 2.0 | 2.5 | 3.0 | 3.5 | 4.0 | 4.5 | 5.0 | |
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Morning Warm-Up - Zone Heat
When a system changes from an unoccupied to an occu- pied mode, or switches from STOPPED to AUTO, or power is applied to a unit with the MWU option, the heater in the unit or external heat will be brought on if the space tem- perature is below the MWU setpoint. The heat will remain on until the temperature reaches the MWU setpoint. If the unit is VAV, then the VAV box/unocc relay will continue to stay in the unoccupied position and the VFD/IGV output will stay at 100% during the MWU mode. When the MWU setpoint is reached and the heat mode is terminated, then the VAV box/unocc relay will switch to the occupied mode and the VFD/IGV output will be controlled by the duct static pressure. During Full Capacity MWU the economizer damper is held closed for as long as it takes to reach setpoint. During Cycling Capacity MWU the economizer damper is allowed to go to minimum position after one hour of operation if setpoint has not been reached.
Compressor Motor Winding Thermostats (2B7S1, 2B17S2, 2B27S5, 2B8S3, 2B18S4 & 2B28S6)
A thermostat is embedded in the motor windings of each Scroll compressor. Each thermostat is designed to open if the motor windings exceeds approximately 221 F. The ther- mostat will reset automatically when the winding tempera- ture decreases to approximately 181 F. Rapid cycling, loss of charge, abnormally high suction temperatures, or the compressor running backwards could cause the thermostat to open. During a request for compressor operation, if the Compressor Module (SCM) detects a problem outside of it's normal parameters, it turns any operating
General Information (Continued)
compressor(s) on that circuit "Off", locks out all compressor operation for that circuit, and initiates a manual reset diag- nostic.
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)
Is a binary input device used on CV & VAV units with Hy- dronic Heat. It is mounted in the heat section and con- nected 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 Mod- ule (1U50) and the Rooftop Module (RTM) to:
a. drive the Hydronic Heat Actuator (4U15) to the full open position.
b. turn the supply fan "Off".
c. closes the outside air damper;
d. turns "On" the SERVICE light at the Remote Panel. e. initiates a "Freezestat" diagnostic to the Human
Interface.
High Duct Temp Thermostats (Optional 3S16, 3S17) Are binary input devices used on CV & VAV applications 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 & 1CB14, 1CB15, 1CB16, 1CB17)
The Scroll Compressors are protected by circuit breakers which interrupt the power supply to the compressors if the current exceeds the breakers “must trip” value. During a re- quest for compressor operation, if the Compressor Module (SCM) 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 ini- tiates 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 modu- lates the economizer (if equipped) and/or stages the me- chanical cooling "On and Off" as required to maintain the zone temperature to within the cooling setpoint deadband.
Zone Temperature - Heating
Relies on input from a sensor located directly in the space, while a system is in the occupied "Heating" mode or an un- occupied period, to stage the heat "on and off" or to modu- late the heating valve (hydronic heat only) as required to maintain the zone temperature to within the heating setpoint deadband. The supply fan will be requested to operate any time there is a requested for heat. On gas heat units, the fan will continue to run for 60 seconds after the furnace is turned off.
Supply Air Tempering
On CV units equipped with staged heat, if the supply air temperature falls 10 F below the occupied heating setpoint temperature while the heater is "Off", the first stage of heat will be turned "On". The heater is turned "Off" when the sup- ply air temperature reaches 10 F above the occupied heat- ing setpoint temperature.
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