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

Space Temperature Reset Example — The occupied coolingset point is set to 73 F. The Reset Ratio is set to 5. The ResetLimit is set to 20° F. The Reset Ratio determines how manydegrees F the temperature is reset. At 72 F, the supply tem-perature will be reset 5 degrees higher. At 71 F, the supplytemperature will be reset 10 degrees higher. At 70 F, the sup-ply temperature will be reset 15 degrees higher. At 69 F, thesupply temperature will be reset 20 degrees higher and theReset Limit will have been reached.SUPPLY AIR TEMPERATURE RESET — Supply air tem-perature reset is used to reset the supply air temperature util-ity. A 4 to 20 mA signal (field-supplied) is required. The re-set option does not require enabling.POWER EXHAUST OPERATION — The optional powerexhaust packages are factory- or field-installed with verticalunits and optionally installed in the return air ductwork forhorizontal applications. The standard (offered with constantvolume or variable air volume units) and the modulating powerexhaust (offered on VAV units) are the two packages offered.The modulating power exhaust package is equipped with afield-adjustable static pressure controller to stage up to 4 powerexhaust stages which will maintain a building static pres-sure. The blue controller located in the control box belowthe control board can be adjusted, by removing the coversand adjusting the set point dial to the desired building pres-sure. The blue controller monitors the 4 individual sequenc-ers which activate the 4 individual power exhaust motors.The standard power exhaust package controls up to 2 stagesof power exhaust to maintain building pressure. The powerexhaust package can be configured to deliver positive or nega-tive building pressure. These power exhaust stages are stagedaccording to a percentage of the economizer dampersposition. Default values are 25% for Stage 1 and 75% forStage 2. This package has set points that are adjustablethrough software (Service Tool, Building Supervisor, orComfortWorks™).SMOKE CONTROL MODES — The 48EJ,EK,EW,EY unitswith an optional expansion board perform fire and smokecontrol modes. The expansion board provides 4 modes whichcan be used to control smoke within the conditioned area.The modes of operation are fire shutdown, pressurization,evacuation, and smoke purge. See Table 19.SMOKE DETECTOR — A smoke detector can be used toinitiate fire shutdown. This can be accomplished by a set ofnormally closed pilot relay contacts which will interrupt powerfrom the 24-v transformer, secondary ‘‘B’’ terminal to thecontrol circuit breaker (CB4). See Fig. 44. The wire that con-nects these two points is white and labeled ‘‘W78.’’NOTE: On standard gas models, the indoor fan will con-tinue to run 45 seconds after the call for heat has been ter-minated. If fire shutdown is initiated the fan will stop im-mediately. No 45-second delay will occur.The smoke detector may be mounted in the return air ductor the supply duct. Carrier does not make recommendationsas to specific smoke detector location due to liabilityconsiderations.INDOOR AIR QUALITY CONTROL — The accessory ex-pansion board and accessory IAQ sensor are required for IAQcontrol. The Carrier sensors operate with a 4 to 20 mA sig-nal. The 4 to 20 mA signal is connected to T11 (+) and T12(−) on the expansion board for the IAQ sensor, and T13 (+)and T14 (−) on the expansion board for the OAQ (OutdoorAir Quality) sensor. The sensor is field-mounted and wiredto the expansion board installed in the unit main control box.The IAQ sensor must be powered by a field-supplied 24-vpower supply (ungrounded). Do not use the unit 24-v powersupply to power the sensor.Once installed, the sensor must be enabled. The sensor isconfigured with default values which may be changed throughnetwork access software. To work properly, the IAQ sensorhigh and low reference points for the sensor that is used mustmatch the configured values. The expansion board reacts toa 4 to 20 mA signal from the IAQ sensor. The low reference(4 mA output) must be configured to the minimum IAQ sen-sor reading. The high reference (20 mA output) must be con-figured to the maximum IAQ sensor reading.The IAQ sensor can be configured to either low or highpriority. The priority value can be changed by the user. Thedefault is low.Low priority — When the priority is set to low, the initialcontrol is to the IAQ set point, but the outside air damperposition will change to its minimum position when the fol-lowing conditions occur:• CV units with sensor — when the space temperature isgreater than the occupied cooling set point plus 2° F orwhen the space temperature is less than the occupiedheating set point minus 2° F.• VAV units and CV units with thermostat — when thesupply-air temperature is less than the supply-air tem-perature set point minus 8° F or when the supply-airtemperature is greater than the supply air temperatureset point plus 5° F for 4 minutes.Table 19 — Smoke Control ModesDEVICE PRESSURIZATION SMOKE PURGE EVACUATION FIRE SHUTDOWNEconomizer 100% 100% 100% 0%Indoor Fan/VFD ON ON OFF OFFPower Exhaust (all outputs) OFF ON ON OFFHeat Stages OFF OFF OFF OFFHIR ON ON OFF OFFLEGENDHIR — Heat Interlock RelayVFD — Variable Frequency DriveFig. 44 — Field-Supplied Smoke Detector Wiring43