Carrier HS070-160 Troubleshooting Manual

Also see for 30HR070: Installation, Start-Up and Service Instructions Installation, Start-Up and Service Instructions

Contents

Each function has one or more subfunctions as shown At initial start-up the valve position is initialized to 0.in Table 2. These functions are defined in greater detail After that, the microprocessor keeps accurate track of thein t K Controls Operation section of this book.Fig. 2 - Keyboard and Display ModuleELECTROWIC EXPANSION VALVE ~ The micro-processor controls the electronic expansion valve throughthe EXV driver module. Inside the expansion valve is alinear actuator stepper motor. To control the steppermotor’s position, the thermistor in the cooler and thethermistor in the lead compressor in each circuit are usedto maintain a 20 F (1 I C) difference. Because the com-pressor sensor is after the compressor motor, which addsapproximately 15 F (8.3 C) superheat, the 20 F (1 I C)control temperature results in U”F to 5 F (2.8 C) super-heat leaving the cooler. This improves the performance ofthe cooler.valve position in order to use this information as input forthe other control functions.The control monitors the superheat and the rate ofchange of superheat to control the position of the valve.The valve stroke is very large; this results in very accuratecontrol of the superheat.The electronic expansion valve is also used to limit themaximum saturated suction temperature to 55 F (12.8 C)to keep from overloading the compressor during highcooler water temperatures. This allows the unit to startwith very warm water temperatures.THERMISTORS ~ The electronic control uses 7 ther-mistors to sense temperatures used to control the opera-tion of the chiller. Sensors are listed in Table 3.CAPACITY CONTROL ~ The control cycles com-pressors and alternately loads and unloads cylinders togive capacity control steps as shown in Table 4. The unitcontrols leaving chilled water temperature. Enteringwater temperature is used by the microprocessor in deter-mining the optimum time to load and unload, but is not acontrol set point.The chilled water temperature set point can be auto-matically reset by the return temperature reset or spaceand outside air temperature reset features.Table 2 - Function and SubfunctionsFUNCTIONS