Carrier SINGLE PACKAGE ROOFTOP UNITS ELECTRIC COOLING/GAS HEATING 48EJ Installation And Service Instructions Manual

Also see for 48EJ: Installation, Start-Up and Service Instructions User manual

Contents

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 power for the crank-case heaters is drawn from the unit incoming power, mainunit power must be on for the heaters to be energized.IMPORTANT: After a prolonged shutdown or serv-ice job, energize the crankcase heaters for 24 hoursbefore starting the compressors.EVAPORATOR FAN MOTOR PROTECTION — A manualreset, calibrated trip, magnetic circuit breaker protects againstovercurrent. Do not bypass connections or increase the sizeof the breaker to correct trouble. Determine the cause andcorrect it before resetting the breaker. If the evaporator-fanmotor is replaced with a different horsepower motor, resiz-ing of the circuit breaker is required. Contact CarrierApplication Engineering.CONDENSER-FAN MOTOR PROTECTION — Eachcondenser-fan motor is internally protected againstovertemperature.HIGH- AND LOW-PRESSURE SWITCHES — If eitherswitch trips, or if the compressor overtemperature switch ac-tivates, that refrigerant circuit will be automatically stopped.See Compressor Lockout Logic section on this page.FREEZE PROTECTION THERMOSTAT (FPT) — Freezeprotection thermostats are located on the evaporator coil foreach circuit. One is located at the top and bottom of eachcircuit. It detects frost build-up and turns off the compressor,allowing the coil to clear. Once the frost has melted, the com-pressor can be reenergized.Relief Devices — All units have relief devices to pro-tect against damage from excessive pressures (i.e., fire). Thesedevices are installed on the suction line, liquid line, and onthe compressor.Power Circuit — A typical power wiring schematic isshown in Fig. 56.Control Circuit, 115-V — This control circuit is pro-tected against overcurrent by a 5.0 amp circuit breaker (CB3).Breaker can be reset. If it trips, determine cause of troublebefore resetting. A typical 115-v control wiring schematic isshown in Fig. 57 and 58.Control Circuit, 24-V — This control circuit is pro-tected against overcurrent by a 3.2 amp circuit breaker (CB4).Breaker can be reset. If it trips, determine cause of troublebefore resetting. A typical 24-v control wiring schematic isshown in Fig. 59 and 60.Compressor Lockout Logic — If any of the safe-ties trip, the circuit will automatically reset (providing thesafety has reset) and restart the compressor in 15 minutes. Ifany of the safeties trip 3 times within a 90-minute period,then the circuit will be locked out and will require manualresetting by turning off either the unit disconnect or the con-trol circuit breaker, or opening the thermostat.Replacement Parts — A complete list of replacementparts may be obtained from any Carrier distributor uponrequest.Fig. 54 — Gas ValveFig. 55 — Main Burner Removal49