Carrier AquaForce B Series Controls, Start-up, Operation, Service And Troubleshooting Instructions

Also see for AquaForce 30XV140: Controls, start-up, operation, service and troubleshooting instructions

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Carrier AquaForce B Series Controls, Start-up, Operation, Service And Troubleshooting Instructions Manual pdf 64 page image

64Fig. 58 — Transducer and Switch LocationsSERVICEEconomizer AssemblyEach circuit on the unit has an economizer assembly, which in-cludes a brazed plate heat exchanger, EXVs, and other compo-nents. See Fig. 59.Electronic Expansion ValveSee Fig. 60 for a cutaway view of the EXV. High-pressure liq-uid refrigerant enters the valve through the top. As refrigerantpasses through the orifice, pressure drops and refrigerantchanges to a 2-phase condition (liquid and vapor). The elec-tronic expansion valve operates through electronically con-trolled activation of a stepper motor. The stepper motor stays inposition unless power pulses initiate the two discrete sets ofmotor stator windings for rotation in either direction. The di-rection depends on the phase 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 largenumber of steps and long stroke results in very accurate controlof the refrigerant flow. The stepper motor has either 3810(main) or 2625 (economizer) steps.MAIN EXV CONTROLThe main EXV is controlled by the SIOB (J17-STPR1). Eachcircuit has thermistors located in the compressor discharge(DGT), compressor motor cavity (SGT) and liquid line leavingthe condenser (LIQT). Each circuit also has a DPT, SPT, andLPT. All the pressure readings as measured by the transducersare converted to saturated temperatures. Liquid pressure trans-ducer (LPT) is converted to saturated liquid temperature (SLT).The main control logic for the EXV uses liquid line subcool-ing, which is the difference between the liquid line saturationtemperature and the liquid line temperature, to control theposition of the EXV. The SIOB module controls the position ofthe electronic expansion valve stepper motor to maintain thesubcooling set point. The EXV control logic has several over-rides, which are also used to control the position of the EXV.• Normal Mode (SUBCOOL)• Low Discharge Superheat (DSH)• Low Suction Pressure (SPMIN)• Maximum Suction Pressure (SPMAX)• EXV Start (START)To view EXV overrides: Main Menu Maintenance Menu EXV Control or Main Menu Maintenance MenuEXVECO Control.Normal Mode (SUBCOOL)This is the normal mode of operation of the EXV. Based on theoperating condition and loading of the compressor, the controlcalculates an optimal subcooling setting to maximize the sys-tem efficiency. The controls accordingly adjust the EXV open-ing to meet this calculated subcooling setting. The range of thesubcooling setting can be altered by using the Network ServiceTool in the Configuration EXV_CFG table.Low Discharge Superheat (DSH)This mode is disabled for 100 sec after the start of the circuit.Control enters this mode when DSH is below 12°F (–11.1°C).The control attempts to drive DSH above 15°F (–9.4°C) byclosing the EXV. In this mode the setpoint is modified anddriven to a value that supports a higher DSH value upon exit ofthe mode. This prevents mode cycling. Mode is exited whenthe DSH is greater than 18°F (–7.8°C) or the average DSH iswithin 1.25° (0.7°C) of 15°F (–9.4°C) and the subcooling isabove the subcooling setpoint.SUCTION PRESSURETRANSDUCER (SPT A)OIL SEPARATOR (A)OIL PRESSURETRANSDUCER (OPT A)ECONOMIZER PRESSURETRANSDUCER (EPT A)LIQUID PRESSURETRANSDUCER (LPT A)EVAPORATOR (B)COMPRESSOR (B)DISCHARGE PRESSURETRANSDUCER (DPT A)SUCTION PRESSURETRANSDUCER (SPT B) OIL PRESSURETRANSDUCER (OPT B)ECONOMIZER PRESSURETRANSDUCER (EPT B)LIQUID PRESSURETRANSDUCER (LPT B) DISCHARGE PRESSURETRANSDUCER (DPT B)OIL LEVEL SWITCH(OIL LS B)EVAPORATOR (A)COMPRESSOR (A)HIGH PRESSURESWITCH (HPS B)HIGH PRESSURESWITCH (HPS A)EVAPORATOR FLOWSWITCH (CWFS)OIL SEPARATOR(B)OIL LEVEL SWITCH(OIL LSA)POWERBOX END