Carrier WeatherExpert 48N2 Controls, Start-up, Operation, Service And Troubleshooting Instructions

Also see for WeatherExpert 48N2: Installation instructions Installation instructions Controls, start-up, operation, service, and troubleshooting Installation instructions

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Carrier WeatherExpert 48N2 Controls, Start-up, Operation, Service And Troubleshooting Instructions Manual pdf 172 page image

172Filter Drier — Replace whenever the moisture/liquid indi-cator shows moisture in the system or when the system wasopened for service.Liquid Line Service Valves — Use caution whenclosing liquid line service valves. The expansion of a trappedliquid can create dangerously high pressures. Remove refriger-ant immediately from trapped sections or attach a hose fromthe high side to the low side of the system to provide relief. Ifequipped with a liquid line solenoid valve in the evaporatorsection, it will be closed during the off-cycle. This creates thepotential for a liquid trap between the solenoid valve and aclosed service valve. Remove refrigerant immediately from thesection or attach a hose for relief.Protective DevicesCOMPRESSOR PROTECTIONOvercurrent — Each compressor has one manual reset,calibrated trip, magnetic circuit breaker. Do not bypass connec-tions or increase the size of the circuit breaker to correct trou-ble. Determine the cause and correct it before resetting thebreaker.Overtemperature — Each compressor has a protector to pro-tect it against excessively high discharge gas temperatures.Additionally, some units contain Copeland compressorsequipped with advanced scroll temperature protection (ASTP).A label located above the terminal box identifies CopelandScroll compressor models that contain this technology. SeeFig. 83. Advanced scroll temperature protection is a form of in-ternal discharge temperature protection that unloads the scrollcompressor when the internal temperature reaches approxi-mately 300 F. At this temperature, an internal bi-metal diskvalve opens and causes the scroll elements to separate, whichstops compression. Suction and discharge pressures balancewhile the motor continues to run. The longer the compressorruns unloaded, the longer it must cool before the bi-metal diskresets. See Fig. 84.To manually reset ASTP, the compressor should be stoppedand allowed to cool. If the compressor is not stopped, the motorwill run until the motor protector trips, which occurs up to90 minutes later. Advanced scroll temperature protection willreset automatically before the motor protector resets, whichmay take up to 2 hours.Crankcase Heater — Each compressor has a crankcase heaterto prevent absorption of liquid refrigerant by oil in the crank-case when the compressor is idle. Since 115-v power for thecrankcase heaters is drawn from the unit control circuit, mainunit power must be on for the heaters to be energized.EVAPORATOR-FAN MOTOR PROTECTION — A manu-al reset, calibrated trip, magnetic circuit breaker protectsagainst overcurrent. Do not bypass connections or increase thesize of the breaker to correct trouble. Determine the cause andcorrect it before resetting the breaker.CONDENSER-FAN MOTOR PROTECTION — Eachcondenser-fan motor is internally protected against over-temperature. They are also protected against a severe over-current condition by manual reset, calibrated trip, magnetic cir-cuit breakers on a common circuit. As with the circuit breakers,do not bypass connections or increase breaker size to correcttrouble. Determine the cause and correct it before resetting thebreaker.HIGH-PRESSURE SWITCHES — Settings for these switch-es are shown in Tables 109 and 110. If either switch trips, thatrefrigerant circuit will be automatically locked out by the con-trols. To reset, set ALARMSR.CUR = YES.Table 109 — Pressure Switch Settings (psig)Table 110 — Pressure Switch Settings (kPa)Temperature Relief Devices — All units have tem-perature relief devices to protect against damage from exces-sive pressures caused by extreme high temperatures (i.e., fire).These devices protect the high and low side.Control Circuit, 115 V — This control circuit is protect-ed against overcurrent by a 10-amp circuit breaker. Breaker canbe reset. If it trips, determine cause of trouble before resetting.Control Circuit, 24 V — This control circuit is protectedagainst overcurrent by two 10-amp and four 3.2-amp circuitbreakers. Breakers can be reset. If a breaker trips, determinecause of trouble before resetting.Gas Heat (48N Only)LIMIT SWITCHES — The maximum supply-air temperatureis controlled by a limit switch located in the gas section. Thelimit is designed to trip at 100 F above the maximum tempera-ture rise.When the limit trips, 2 flashes occur on the IGC board. Thegas valve is de-energized. After cooling, the system will resetand fires gas again. If four trips occur, the system shuts downinto Lockout and 4 flashes occur on the IGC board. The systemIMPORTANT: After a prolonged shutdown or servicejob, energize the crankcase heaters for 24 hours beforestarting the compressor.Fig. 83 — Advanced Scroll TemperatureProtection LabelSWITCH CUTOUT CUT-INHigh 650  10 500  15SWITCH CUTOUT CUT-INHigh 4482  69 3447  10301020304050607080901001101200 10 20 30 40 50 60 70 80 90Compressor Unloaded Run Time (Minutes)Recommended Cooling Time(Minutes)*Times are approximate.NOTE: Various factors, including high humidity, high ambient tem-perature, and the presence of a sound blanket will increase cool-down times.Fig. 84 — Recommended Minimum Cool-DownTime After Compressor is Stopped*