Carrier AQUAFORCE 30XA080-500 Controls, Start-up, Operation, Service And Troubleshooting Instructions

Also see for AQUAFORCE 30XA080: Installation instructions Controls, start-up, operation, service and troubleshooting instructions Installation instructions Product data

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Carrier AQUAFORCE 30XA080-500 Controls, Start-up, Operation, Service And Troubleshooting Instructions Manual pdf 74 page image

74Table 47B — 5K Thermistor Temperature (°C) vs Resistance/VoltageSERVICEEconomizer Assembly — Each circuit on the30XA090-500 units has an economizer assembly. The30XA080,082 units do not have an economizer and have onemain electronic expansion valve. The 30XA080,082 units arecontrolled the same way as units with a separate economizerassembly. See Fig. 46.Electronic Expansion Valve (EXV) — See Fig. 47for a cutaway view of the EXV. High-pressure liquid refriger-ant enters valve through the top. As refrigerant passes throughthe orifice, pressure drops and refrigerant changes to a 2-phasecondition (liquid and vapor). The electronic expansion valveoperates through an electronically controlled activation of astepper motor. The stepper motor stays in position unless pow-er pulses initiate the two discrete sets of motor stator windingsfor rotation in either direction. The direction depends on thephase relationship of the power pulses.The motor directly operates the spindle, which has rotatingmovements that are transformed into linear motion by thetransmission in the cage assembly. The valve cone is a V-porttype which includes a positive shut-off when closed.The large number of steps and long stroke results in very ac-curate control of the refrigerant flow. The stepper motor has ei-ther 3690 (main) or 2785 (economizer) steps.FLOODED COOLER MAIN EXV CONTROL — Eachcircuit has a thermistor located in the discharge end of the com-pressor (DGT) and another one located in the compressor mo-tor cavity (SGT). Each circuit also has discharge and suctionpressure transducer. Discharge and suction pressure as mea-sured by the transducers are converted to saturated tempera-tures. The main control logic for the EXV uses discharge su-perheat to control the position of the EXV. The difference be-tween the temperature of the discharge gas and the saturateddischarge temperature is the superheat. The EXV module con-trols the position of the electronic expansion valve stepper mo-tor to maintain the discharge superheat set point.The EXV control logic has several overrides, which are alsoused to control the position of the EXV.• Approach between SST (Saturated Suction Temperature)and LWT• Maximum Operating Pressure (MOP)Approach — If the approach (pinch), which is the differencebetween leaving fluid temperature and saturated suction tem-perature, is equal to or less than the pinch set point then theEXV will not open any further even though discharge super-heat set point is not met. Pinch set point is calculated usingsuction superheat, discharge superheat and pinch offset. Pinchoffset is used to adjust calculated pinch set point do to accuracyof transducers and thermistors.MOP — The EXV is also used to limit cooler saturated suctiontemperature to 62 F (16.6 C). This makes it possible for thechiller to start at higher cooler fluid temperatures without over-loading the compressor. This is commonly referred to as MOP(maximum operating pressure). If the SST is equal to or greaterthan the MOP set point then the MBB will try to control theEXV position to maintain the MOP set point.TEMP(C) RESISTANCE(Ohms)–32 100,260–31 94,165–30 88,480–29 83,170–28 78,125–27 73,580–26 69,250–25 65,205–24 61,420–23 57,875–22 54,555–21 51,450–20 48,536–19 45,807–18 43,247–17 40,845–16 38,592–15 38,476–14 34,489–13 32,621–12 30,866–11 29,216–10 27,633–9 26,202–8 24,827–7 23,532–6 22,313–5 21,163–4 20,079–3 19,058–2 18,094–1 17,1840 16,3251 15,5152 14,7493 14,0264 13,3425 12,6966 12,0857 11,5068 10,9599 10,44110 9,94911 9,48512 9,04413 8,62714 8,231TEMP(C) RESISTANCE(Ohms)15 7,85516 7,49917 7,16118 6,84019 6,53620 6,24621 5,97122 5,71023 5,46124 5,22525 5,00026 4,78627 4,58328 4,38929 4,20430 4,02831 3,86132 3,70133 3,54934 3,40435 3,26636 3,13437 3,00838 2,88839 2,77340 2,66341 2,55942 2,45943 2,36344 2,27245 2,18446 2,10147 2,02148 1,94449 1,87150 1,80151 1,73452 1,67053 1,60954 1,55055 1,49356 1,43957 1,38758 1,33759 1,29060 1,24461 1,200TEMP(C) RESISTANCE(Ohms)62 1,15863 1,11864 1,07965 1,04166 1,00667 97168 93869 90670 87671 83672 80573 77574 74775 71976 69377 66978 64579 62380 60281 58382 56483 54784 53185 51686 50287 48988 47789 46690 45691 44692 43693 42794 41995 41096 40297 39398 38599 376100 367101 357102 346103 335104 324105 312106 299107 285