Carrier 30HXC Installation, Operation And Maintenance Instructions

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

Contents

Carrier 30HXC Installation, Operation And Maintenance Instructions Manual pdf 40 page image

4010.3 - Electronic expansion device (EXV)The microprocessor controls the EXV through the EXV controlmodule. Inside this EXV is a linear actuator stepper motor. High-pressure liquid refrigerant enters the valve through the bottom. Aseries of calibrated slots are located inside the orifice assembly.As refrigerant passes through the orifice, the pressure drops andthe refrigerant changes to a 2-phase condition (liquid and vapour).To control refrigerant flow for different operating conditions, thesleeve moves up and down over the orifice, thereby changingeffective flow area of expansion device. The sleeve is moved bya linear stepper motor. The stepper motor moves in incrementsand is controlled directly by the processor module. As the steppermotor rotates, motion is transferred into linear movement by thelead screw. Through the stepper motor and lead screws, 1500discrete steps of motion are obtained. The large number of stepsand long stroke result in very accurate control of refrigerant flow.At initial start-up, the EXV position is at zero. After that, themicroprocessor keeps accurate track of the valve position in orderto use this information as input for the other control functions. Itdoes this by initializing the EXV’s at startup. The processor sendsout enough closing pulses to the valve to move it from fully opento fully closed, then resets the position counter to zero. From thispoint on, until the initialization, the processor counts the totalnumber of open and closed steps it has sent to each valve.10.4 - EconomizerEconomizers are installed on 30HXC 190, 285 and 375.The economizer improves both the chiller capacity and efficiency aswell as providing motor cooling. The economizers used are direct-expansion plate heat exchangers.The flow of the direct-expansion plate heat exchanger circuit isadjusted by the thermostatic cooling valves.10.5 - Oil pumpsThe 30HXC screw chillers use one externally mountedpre-lubricating oil pump per circuit. This pump is operated as partot the start-up sequence.ATTENTION: The operating temperature of the coil may reach80°C. In certain temporary conditions (especially duringstart-up at low outside temperature or low condenser looptemperature) the oil pump can be reactivated.10.6 - 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 with economizers with plate heat exchangers,a thermostatic valve controls the necessary refrigerant flow enteringthis heat exchanger and continuously flowing over the motorwindings. All refrigerant used for motor cooling returns to the rotorsand is compressed to the discharge pressure.10.7 - SensorsThe units use thermistors to measure the temperature, and pressuretransducers to control and regulate system operation (see 30GX/HXC - Pro-Dialog Plus Control IOM for a more detailedexplanation).