Carrier AquaSnap 30MPA Series Controls, Start-up, Operation, Service, And Troubleshooting

Also see for AQUASNAP 30MPA: User manual Operation and service manual Installation instructions

Carrier AquaSnap 30MPA Series Controls, Start-up, Operation, Service, And Troubleshooting Manual pdf 41 page image

41valve solenoid (if installed), cooler pump, EXV, and remotealarm relay. To use the Service Test mode, the Enable/Off/Re-mote Control switch must be in the OFF position. Use the dis-play keys to enter the mode and display TEST. Presstwice so that OFF flashes. Enter the password if required. Useeither arrow key to change the TEST value to the ON positionand press . Move the Enable/Off/Remote Controlswitch to enable. Press and the button to enterthe OUTS or COMP sub-mode. ENABLE/OFF/REMOTEswitchmust be set to ENABLE to operate test.NOTE: Cooler and condenser (30MPW) water flow must beestablished in order to operate compressor in service test.Test the condenser output, cooler pump, liquid line solenoidvalve (30MPA only), crankcase heater, water valve (accesso-ry), and alarm relay by changing the item values from OFF toON. These discrete outputs are then turned off if there is nokeypad activity for 10 minutes. When testing compressors, thelead compressor must be started first. All compressor outputscan be turned on, but the control will limit the rate by stagingone compressor per minute. Minimum load valve can be testedwith the compressors on or off. The relays under the COMPmode will stay on for 10 minutes if there is no keypad activity.Compressors will stay on until they are turned off by the opera-tor. The Service Test mode will remain enabled for as long asthere is one or more compressors running. All safeties are mon-itored during this test and will turn a compressor, circuit or themachine off if required. Any other mode or sub-mode can beaccessed, viewed, or changed during the TEST mode. TheSTAT item (Run StatusVIEW) will display “0” as long asthe Service mode is enabled. The TEST sub-mode value mustbe changed back to OFF before the chiller can be switched toEnable or Remote control for normal operation.Charging — For 30MPW units, when service is required,recover the refrigerant from the system.For 30MPA units when service is required, the compressorand evaporator can be serviced by closing the factory-installedliquid line service valve and field-installed discharge line ser-vice valve. After the valves are closed, recover the refrigerantfrom the system.Electronic ComponentsCONTROL COMPONENTS — Unit uses an advanced elec-tronic control system that normally does not require service.For details on controls refer to Controls section.Access to the controls is through a hinged panel. Inner pan-els are secured in place and should not be removed unless allpower to the chiller is off.Electronic Expansion Valve (EXV) (30MP050-071 Only) — See Fig. 26 for a cutaway view of the EXV.High-pressure liquid refrigerant enters valve through the top.As refrigerant passes through the orifice, pressure drops and re-frigerant changes to a 2-phase condition (liquid and vapor).The electronic expansion valve operates through an electroni-cally controlled activation of a stepper motor. The stepper mo-tor stays in position, unless power pulses initiate the two dis-crete sets of motor stator windings for rotation in either direc-tion. The direction depends on the phase relationship of thepower pulses.As the stepper motor rotates, its motion is transferred to lin-ear movement by a lead screw. Refrigerant flow is modulatedby either opening or closing the port. The valve includes a pos-itive shut-off when closed.Table 40 shows the number of steps for the EXV. The EXVmotor moves at 150 steps per second. Commanding the valveto either 0% or 100% will add extra steps to the move, to en-sure the value is open or closed completely.Table 40 — EXV StepsThe EXV board controls the valve. Each circuit has athermistor located in a well in the suction manifold before thecompressor. Suction pressure as measured by the suction pres-sure transducer is converted to a saturated suction temperature.The thermistor measures the temperature of the superheatedgas entering the compressor and the pressure transducer deter-mines the saturated temperature of suction gas. The differencebetween the temperature of the superheated gas and the saturat-ed suction temperature is the superheat. The EXV boardcontrols the position of the electronic expansion valve steppermotor to maintain superheat set point.The MBB controls the superheat leaving cooler to approxi-mately 9° F (5° C). Because EXV status is communicated tothe main base board (MBB) and is controlled by the EXVboards, it is possible to track the valve position. The unit is thenprotected against loss of charge and a faulty valve. Just prior tocompressor start, the EXV will open. At low ambient tempera-tures the EXV is closed at start up. After initialization period,valve position is tracked by the EXV board by constantlymonitoring the amount of 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 chiller tostart at higher cooler fluid temperatures without overloadingthe compressor. This is commonly referred to as MOP (maxi-mum operating pressure).If it appears that the EXV module is not properly con-trolling circuit operation to maintain correct superheat, thereare a number of checks that can be made using test functionsand initialization features built into the microprocessor control.See the EXV Troubleshooting Procedure section to test EXVs.ENTERENTERESCAPEUNIT SIZE 30MP EXV STEPS050-071 36901. Cable2. Glass Seal3. Motor Housing4. Stepper Motor5. Bearing6. Lead Screw7. Insert8. Valve Piston9. Valve Seat10. Valve PortFig. 26 — Cutaway View of the ElectronicExpansion Valve (Sizes 050-071)