Carrier AQUASNAP MPW015-045 Operation And Service Manual

Also see for AQUASNAP 30MPA: User manual Installation instructions Controls, start-up, operation, service, and troubleshooting

38MINIMUM LOAD VALVE — On units equipped with thefactory-installed hot gas bypass option, a solenoid valve anddischarge bypass valve (minimum load valve) are locatedbetween the discharge line and the cooler entering-refrigerantline. The MBB cycles the solenoid to perform minimum loadvalve function and the discharge bypass valve modulates to thesuction pressure set point of the valve. The bypass valve has anadjustable opening setting between 95 to 115 psig (655 to793 kPa). The factory setting is 105 psig (724 kPa).The amount of capacity reduction achieved by the mini-mum load valve is not adjustable. The total unit capacity withthe minimum load valve is shown in Table 19.PRESSURE RELIEF DEVICES — All units have one pres-sure relief device per circuit located in the liquid line which re-lieves at 210 F (100 C).The 30MPW unit does not have a condenser pressure reliefvalve, because the brazed-plate condenser is not considered apressure vessel, as defined in ANSI/ASHRAE 15 (AmericanNational Standards Institute/American Society of Heating,Refrigerating, and Air Conditioning Engineers) safety coderequirements.For 30MPA condenserless units, pressure relief devices de-signed to relieve at the pressure determined in local codes,must be field-supplied and installed in the discharge line pipingin accordance with ANSI/ASHRAE 15 safety code require-ments. Additional pressure relief valves, properly selected,must be field-supplied and installed to protect high side equip-ment and may be required by applicable codes.Most codes require that a relief valve be vented directly tothe outdoors. The vent line must not be smaller than the reliefvalve outlet. Consult ANSI/ASHRAE 15 for detailed informa-tion concerning layout and sizing of relief vent lines.Check Unit SafetiesHIGH-PRESSURE SWITCH — A high-pressure switch isprovided to protect each compressor and refrigeration systemfrom unsafe high pressure conditions. See Table 31 for high-pressure switch settings.The high-pressure switch is mounted in the discharge line ofeach circuit. If an unsafe, high-pressure condition should exist,the switch opens and shuts off the affected circuit. The CSB(current sensing board) senses the compressor feedback signaland generates an appropriate alarm. The MBB prevents the cir-cuit from restarting until the alert condition is reset. The switchshould open at the pressure corresponding to the appropriateswitch setting as shown in Table 31.Table 31 — Factory Settings, High-PressureSwitch (Fixed)Clear the alarm using the scrolling marquee display. Theunit should restart after the compressor anti-short-cycle delay,built into the unit control module, expires.PRESSURE TRANSDUCERS — Each unit is equipped witha suction and discharge pressure transducer. These inputs to theMBB are not only used to monitor the status of the unit, but toalso maintain operation of the chiller within the compressormanufacturer's specified limits. The input to the MBB from thesuction pressure transducer is also used to protect the compres-sor from operating at low pressure conditions. If suction returngas thermistors are installed, then additional low superheatconditions are detected. In some cases, the unit may not be ableto run at full capacity. The control module will automaticallyreduce the capacity of a circuit as needed to maintain specifiedmaximum/minimum operating pressures.COOLER FREEZE-UP PROTECTIONThe main base board (MBB) monitors cooler leaving fluidtemperature at all times. The MBB will rapidly remove stagesof capacity as necessary to prevent freezing conditions due tothe rapid loss of load or low cooler fluid flow.When the cooler is exposed to lower temperatures (40 F[4.4 C] or below), freeze-up protection is required using inhib-ited ethylene or propylene glycol.Thermistors — Electronic control uses up to five 5 kthermistors to sense temperatures used to control operation ofthe chiller. Thermistors EWT, LWT, RGTA, CNDE, CNDL,and OAT are identical in their temperature and voltage dropperformance. The SPT space temperature thermistor has a10 k input channel and it has a different set of temperature vs.resistance and voltage drop performance. Resistance at varioustemperatures are listed in Tables 32-35. For dual chiller opera-tion, a dual chiller sensor is required which is a 5 kthermistor.REPLACING THERMISTORS (EWT, LWT, RGT, CNDE,CNDL) — Add a small amount of thermal conductive greaseto the thermistor well and end of probe. For all probes, tightenthe retaining nut ¼ turn past finger tight. See Fig. 22.THERMISTOR/TEMPERATURE SENSOR CHECK — Ahigh quality digital volt-ohmmeter is required to perform thischeck.1. Connect the digital voltmeter across the appropriate the-mistor terminals at the J8 terminal strip on the main baseboard (see Fig. 23).2. Using the voltage reading obtained, read the sensor tem-perature from Tables 32-35.3. To check thermistor accuracy, measure temperature atprobe location with an accurate thermocouple-type tem-perature measuring instrument. Insulate thermocouple toavoid ambient temperatures from influencing reading.Temperature measured by thermocouple and temperaturedetermined from thermistor voltage reading should beclose, ± 5° F (3° C) if care was taken in applying thermo-couple and taking readings.If a more accurate check is required, unit must be shut downand thermistor removed and checked at a known temperature(freezing point or boiling point of water) using either voltagedrop measured across thermistor at the J8 terminal, by deter-mining the resistance with chiller shut down and thermistordisconnected from J8. Compare the values determined with thevalue read by the control in the Temperatures mode using thescrolling marquee display.Pressure Transducers — The suction and dischargetransducers are different part numbers and can be distinguishedby the color of the transducer body, suction (yellow) and dis-charge (red). No pressure transducer calibration is required.The transducers operate on a 5 vdc supply, which is generatedby the main base board (MBB). See Fig. 23 for transducer con-nections to the J8 connector on the MBB.TROUBLESHOOTING — If a transducer is suspected of be-ing faulty, first check supply voltage to the transducer. Supplyvoltage should be 5 vdc ± 0.2 v. If supply voltage is correct,compare pressure reading displayed on the scrolling marqueedisplay module against pressure shown on a calibrated pressureUNIT CUTOUT CUT-INPsig kPa Psig kPa30MP015-045 650 4482 500 3447WARNINGOn medium temperature brine units, the anti-freeze solu-tion must be properly mixed to prevent freezing at a tem-perature of at least 15 F (8.3 C) below the leaving-fluidtemperature set point. Failure to provide the proper anti-freeze solution mixture is considered abuse and may impairor otherwise negatively impact the Carrier warranty.