Trane SCXG-SVX01B-EN general Operation information, Low Ambient Control Air-CooledUnits Only

general

Operation information

Water-cooled:Units withoutWSE, the condenser valve modulates to maintain an average saturated condenser tem- perature. Units withWSE, if economizing and mechanical cooling is necessary the economize valve will sacrifice free cooling and modulate to maintain condensing saturated temperature. If not economizing, the condenser valve will modulate to maintain condensing saturated temperature.

Water-cooled units without head pres- sure control will lock out mechanical cooling at entering condenser water temperatures below 54°F. Mechanical cooling will resume when the entering condenser water temperature exceeds 58°F.

Low Ambient Control (Air-Cooled Units Only)

The low ambient modulating output on the compressor module is functional on all units with or without the low ambient option. When the compressor module stages up to it's highest stage (stage 2 or 3 depending on unit size), the modulating output is 100% (10 VDC). When the control is at stage 1, the modulating output (0-10 VDC) controls the saturated condensing temperature to within the programmable condensing temperature low ambient control point.

Low Ambient Compressor Lockout (Air- Cooled Units Only)

The low ambient compressor lockout utilizes an analog input device. When the system is configured for low ambient compressor lockout, the compressors will not operate if the temperature of the outside air falls below the lockout setpoint. When the temperature rises 5°F above the lockout setpoint, the compressors will operate. The setpoint 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 panel.

Return AirTemperature Sensor

The return air temperature sensor is an analog input device used with a return humidity sensor on units with the comparative enthalpy option.The sensor monitors the return air temperature and compares it to the outdoor temperature to establish which temperature is best

suited to maintain cooling requirements. It is mounted in the return air path and connected to the ECEM.

Supply Fan Circuit Breaker, Fuses, and Overloads

The supply fan motor is protected by either circuit breakers fuses or a combination of fuses and overloads, dependent upon unit configuration. Circuit breakers are used on units without aVFD.They will trip and interrupt the motor power supply if the current exceeds the breaker trip value.The RTM shuts all system functions off when detecting an open fan proving switch. Units with a VFD have fuses to protect theVFD and motor. Units with aVFD w/ bypass have fuses to protect VFD circuit and overloads to protect the motor when in bypass.

Supply Air Temperature Low Limit The supply air temperature low limit function uses the supply air temperature sensor input to modulate the economizer damper to the minimum position if the supply air temperature falls below the occupied heating setpoint temperature.

Supply Air Temperature Sensor

The supply air temperature sensor is an analog input device. It monitors the supply air temperature for supply air temperature control, supply air temperature reset, supply air temperature low limiting, and supply air tempering. It is mounted in the supply air discharge section of the unit and connected to the RTM.

Supply Airflow Proving Switches

This is binary input device used on units to signal the RTM when the supply fan is operating. It is mounted in the supply fan section and is connected to the RTM.

During a request for fan operation and if the differential switch opens for 40 consecutive seconds, compressor operation turns off, heat operation turns off, the request for supply fan operation is turns off and locks out, IGV option closes, economizer damper option closes, and a manual reset diagnostic initiates.

Low Entering Air Protection Device (LEATPD)

The low entering air protection device (LEATPD) is a binary input on units with hydronic heat or a waterside economizer. It is optional on water-cooled units.

If the LEATPD is on a unit with factory- installed heat, it is mounted in the heat section and connected to the heat module. If the entering air temperature to the heating coil falls to 40°F, the normally open contacts on the LEATPD close and cause the following events:

a. the hydronic heat actuator fully opens. b. the supply fan turns off

c. the outside air damper closes

d. the SERVICE light at the remote zone sensor option turns on.

e. a LEATPD diagnostic displays at the human interface panel.

If the LEATPD is on a water-cooled unit without factory-installed heat, it is wired to the WSM. It will trip if the entering water temperature falls to 34°F, open the economizer valve, and energize the pump output.

High DuctTempThermostat Option On Units with an LCI-I

The high duct temperature thermostats are binary input devices used on units with aTrane communication interface module (Tracer/LCI-I).They provide a high limit unit shutdown and require a manual reset.The thermostats 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 requires a manual reset. Reset by pressing the sensor’s reset button when the air temperature decreases approximately 25°F below the cutout point.

Filter Switch

The filter switch is a binary input device that measures the pressure differential across the unit filters. It is mounted in the filter section and connected to the RTM. A diagnostic SERVICE signal displays at the remote panel if the pressure differential across the filters is at least 0.5” w.c.The contacts automatically open when the pressure differential across the filters decrease to 0.4” w.c.The switch differential is field adjustable between 0.17” to 5.0” w.c. ± 0.05 “.

High Duct Static Switch Option The high duct static switch is field- mounted in the ductwork or plenums with smoke dampers. It will cause a manual reset diagnostic if the duct static exceeds the pre-set static limit.The static limit is adjustable at the HI.

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