Carrier 30HXC Series Installation, Operation And Maintenance Instructions

Also see for 30GX Series: Installation, operation and maintenance instructions Installation, operation and maintenance instructions

Carrier 30HXC Series Installation, Operation And Maintenance Instructions Manual pdf 27 page image

27desired liquid level in the cooler (as is done for Non-Economized chillers). The float valve maintains a liquid levelin the bottom of the economizer. Liquid refrigerant is suppliedfrom the condenser to the bottom of the economizer. As therefrigerant passes through the EXV, its pressure is reduced toan intermediate level of about 500 kPa. This pressure ismaintained inside the economizer shell. Next, the refrigerantflows through the float valve, its pressure is further reduced toslightly above the pressure in the cooler. The increase inperformance is realized when some of the refrigerant passingthrough the EXV flashes to vapor, further subcooling the liquidthat is maintained at the bottom of the economizer. Thisincrease in subcooling provides additional capacity. Since noadditional power is required to accomplish this, the efficiencyof the machine also improves. The vapor that flashes will riseto the economizer where it passes to the compressor and isused as needed to provide motor cooling. After passing overthe motor windings, the refrigerant reenters the cycle at anintermediate port in the compression cycle.14.7 - Oil pumpsThe 30GX/HXC screw chillers use one externally mountedpre-lubricating oil pump per circuit. This pump is operated aspart ot the start-up sequence.ATTENTION: The operating temperature of the coil mayreach 80°C. In certain temporary conditions (especiallyduring start-up at low outside temperature or low condenserloop temperature) the oil pump can be reactivated.On 30GX units, the pumps are mounted to the base rails on theoil separator side of the unit. The pumps are mounted to abracket on the condensers of 30HXC units. When a circuit isrequired to start, the controls will energize the oil pump first sothat the compressor starts with correct lubrication. If the pumphas built up sufficient oil pressure, the compressor will beallowed to start. Once the compressor has started, the oil pumpwill be turned off. If the pump was not able to build up enoughoil pressure, the control will generate an alarm.14.8 - Motor cooling valvesCompressor motor winding temperatures are controlled to theoptimum setpoint. The control accomplishes this by cycling themotor cooling solenoid valve to allow liquid refrigerant to flowacross the motor windings as needed. On units equipped witheconomizers, flash gas leaves the top of the economizer andcontinually flows to the motor windings. All refrigerant usedfor motor cooling re-enters the rotors through a port locatedmidway along the compression cycle and is compressed todischarge pressure.14.9 - SensorsThe units use thermistors (including two motor temperaturethermistors) and two level thermistors and pressure transducersto monitor and control system operation.14.10 - Thermistors14.10.1 - Evaporator leaving fluidThis temperature is used to measure the leaving evaporatorfluid temperature (water or brine). The temperature is used forleaving fluid temperature control and to protect against coolerfreeze-up. It is located in the evaporator fluid nozzle.14.10.2 - Evaporator entering fluidThis sensor is used to measure the evaporator entering fluidtemperature. It is located in the entering evaporator nozzle. It isused to provide automatic temperature compensation for theleaving fluid temperature control with entering fluid compen-sation.14.10.3 - Discharge gas temperature (circuits A & B)This sensor used to measure the discharge gas temperature andcontrol the discharge temperature superheat. It is located on thedischarge pipe of each circuit (30HXC) or on the top of the oilseparator (30GX).ATTENTION: There is no thermostat sleeve.14.10.4 - Motor temperatureThe Compressor Protection Module (CPM) monitors the motortemperature. Thermistor terminals are located in thecompressor junction box.14.10.5 - Evaporator liquid level (circuits A & B)Evaporator liquid level thermistor is used to provide optimizedflow control in the evaporator. It is installed in the top of theevaporator.14.10.6 - Condenser entering fluid (30HXC)This sensor is used to measure the temperature of the fluidentering the water cooled condensers. It is located in thecommon fluid line entering the condensers (field installed). OnHeat Machines it is used by the capacity control routine. Onwater cooled condensers it is only used for monitoring of thecondenser fluid temperature.14.10.7 - Condenser leaving fluid (optional on 30HXC)This sensor is used to measure the temperature of the fluidleaving the water cooled condensers. It is located in thecommon fluid line leaving the condensers (field installed). OnHeat Machines it is used by the capacity control routine. Onwater cooled condensers it is only used for monitoring of thecondenser fluid temperature.