Carrier 30GTN Service And Troubleshooting Manual

Also see for 30GTN: Product data Installation instructions Installation instructions

Carrier 30GTN Service And Troubleshooting Manual Manual pdf 56 page image

Refrigerant Feed Components — Each circuit hasall necessary refrigerant controls.ELECTRONIC EXPANSION VALVE (EXV) — A cutawayview of valve is shown in Fig. 28.High-pressure liquid refrigerant enters valve through bot-tom. A series of calibrated slots have been machined in sideof orifice assembly. As refrigerant passes through orifice, pres-sure drops and refrigerant changes to a 2-phase condition(liquid and vapor). To control refrigerant flow for differentoperating conditions, a sleeve moves up and down over ori-fice and modulates orifice size. A sleeve is moved by a linearstepper motor. Stepper motor moves in increments and is con-trolled directly by EXV module. As stepper motor rotates,motion is transferred into linear movement by lead screw.Through stepper motor and lead screw, 1500 discrete stepsof motion are obtained. The large number of steps and longstroke results in very accurate control of refrigerant flow. Theminimum position for operation is 120 steps.The EXV module controls the valve. The lead compressorin each circuit has a thermistor located in the suction mani-fold after the compressor motor and a thermistor located ina well where the refrigerant enters the cooler. The ther-mistors measure the temperature of the superheated gas en-tering the compressor cylinders and the temperature of therefrigerant entering the cooler. The difference between thetemperature of the superheated gas and the cooler suctiontemperature is the superheat. The EXV module controls theposition of the electronic expansion valve stepper motor tomaintain 29 F (16 C) superheat.The superheat leaving cooler is approximately 3° to 5° F(2° to 3° C), or less.Because EXV status is communicated to the Main BaseBoard (MBB) and is controlled by the EXV modules (seeFig. 27), it is possible to track the valve position. By thismeans, head pressure is controlled and unit is protected againstloss of charge and a faulty valve. During initial start-up, EXVis fully closed. After initialization period, valve position istracked by the EXV module by constantly monitoring amountof valve movement.The EXV is also used to limit cooler saturated suction tem-perature to 50 F (10 C). This makes it possible for the chillerto start at higher cooler fluid temperatures without overload-ing the compressor. This is commonly referred to as MOP(maximum operating pressure).If it appears that EXV is not properly controlling circuitoperation to maintain correct superheat, there are a numberof checks that can be made using test functions and initial-ization features built into the microprocessor control. See Serv-ice Test section on page 29 to test EXVs.DIMENSION FAN TYPEStandard Low Noise (Optional)A 0.509 (13 mm) 1.509 (38 mm)B 0.889 (22 mm) 1.139 (29 mm)NOTE: Fan rotation is clockwise as viewed from top of unit.Fig. 26A — Condenser Fan Adjustment —Standard 50 and 60 Hz Units and60 Hz Low Noise Fan Option UnitsPLASTIC FANPROPELLERCLEARANCEOF 0.25 INCHES(6.4 MM)FAN DECKSURFACEFAN ORIFICEFig. 26B — Condenser Fan Adjustment —50 Hz Low Noise Fan Option UnitsNOTE: Dimensions are in millimeters. Dimensions in [ ] are in inches.Fig. 27 — Condenser Fan Adjustment,Units with High-Static Fan OptionFig. 28 — Electronic Expansion Valve (EXV)56