Carrier 48MPD Installation, Start-up And Service Instructions Manual

Contents

GeneralNOTE: If unit is equipped with REMOTE START function,place the LOCAL/REMOTE switch in the LOCAL (Off)position.1. Put the ON/OFF switch in the ON position. Close the con-trol circuit breaker (CCB), which will energize the con-trol circuit and the crankcase heaters.2. Using the HSIO or Building Supervisor, verify that noalarms have been detected.3. Ensure that quick test has been performed to make surethat the controls are operating properly. Refer to the Con-trols and Troubleshooting Guide for more information.4. Using the HSIO, put the unit into Run mode.a. Press .b. Press .CLEARc. Press . This will put the unit in Run mode.d. Press . The unit will change from mode 25(standby), to mode 32 (occupied) or mode 27 (unoc-cupied) depending on the programmed timeschedule.Operating Sequences — Base unit operatingsequences are presented below. Refer to unit Controls andTroubleshooting literature for expanded details on unit con-trols operation, additional controls functions, and logic theory.SUPPLY FANVAV Units — During Occupied periods, the control will en-ergize the supply fan contactor. The contactor will close,energizing supply fan motor. Fan wheel will turn. AirflowSwitch (differential pressure switch) contacts close, provid-ing discrete input (DI) to Channel 12 (Closed = Fan ON).Fan operation will continue through the Occupied period.During Unoccupied period with demand, the control willenergize fan contactor when demand is sensed. After fan sta-tus is confirmed, operating routines will start. When demandis removed, routines will end and fan will shut off.CV Units, Continuous Fan — During Occupied periods, thecontrol will energize the supply fan contactor. The contactorwill close, energizing supply fan motor. Fan wheel will turn.Airflow Switch (differential pressure switch) contacts close,providing discrete input (DI) to Channel 12 (Closed =Fan ON). Fan operation will continue through the Occupiedperiod.During Unoccupied period with demand, the control willenergize fan contactor when demand is sensed. After fan sta-tus is confirmed, operating routines will start. When demandis removed, routines will end and fan will shut off.CV Units, Automatic Fan — Fan will be turned OFF duringOccupied period when there is no demand for heating or cool-ing operation. When demand is sensed, control will energizefan contactor and initiate cooling cycle. Fan status will beconfirmed. When demand is removed, routines will termi-nate and fan will be shut off.ECONOMIZER — The economizer control loop will be de-layed 2 minutes after the supply fan is turned ON, to allowsystem and temperatures to stabilize before starting control.When coming out of STANDBY or Heating mode, a 4-minutedelay will occur before the economizer damper is con-trolled. During this delay, damper position is limited to CLOSEDor MINIMUM position (depending on current unit occu-pancy status).If fan status is OFF, the outside air dampers will remainclosed (return air dampers will be open). If fan status is ON,the outside air dampers will normally be at minimum damperposition.Economizer operation is permitted if the system is not inHeating mode, if outdoor air enthalpy (via switch or humid-ity differential) is acceptable, and if outside air temperatureis less than space temperature.If economizer operation is permitted, the ecomizer con-trol loop checks for Cooling System operation. If ON, theoutside air dampers will be driven to maximum position.If cooling is not on , for VAV units, the economizer willmodulate to satisfy the supply air set point.If cooling is not on, for CV units, the economizer willmodulate to satisfy the space temperature set point.If Economizer operation is not permitted, the outside airdampers will be driven to minimum position (during Occu-pied period) or closed (during Unoccupied period).For VAV units, Economizer operation is not permitted whenOccupied Heating is enabled and the Return Air Tempera-ture is LESS THAN (OHSP + 1).COOLING (All Units) — The controls try to control the supply-air temperature (SAT) to a system-calculated coil referencetemperature value by cycling the compressors and theunloader(s). Both the supply- and return-air temperature sen-sors are used to adjust the cycling deadband to match theactual load. The control system provides cooling capacitycontrol of up to 11 stages to maintain supply-air temperature(VAV) or space temperature (CV) to an occupied or un-occupied set point. Automatic lead-lag circuit switchingoccurs (if configured) to equalize run times per compressorfor improved compressor reliability. The compressor to startfirst is changed every time stage equals zero.NOTE: Automatic lead/lag should be disabled if optional hotgas bypass is employed because the unit only contains hotgas bypass on one circuit.The VAV control system sequence uses the modified supply-air set point (MSAT = supply-air set point 1 reset value) asthe supply-air temperature required to satisfy conditions (sub-master reference value [CSSR]) and outputs this value to thesubmaster loop.The submaster loop uses the modified supply-air set pointcompared to the actual supply-air temperature to determinethe required number of capacity stages to satisfy the load.The logic for determining when to add or subtract a stage isa time-based integration of the deviation from the set pointplus the rate of change of the supply-air temperature.The CV control system sequence reads the space sensorand performs a calculation to determine the supply-air tem-perature required (a cooling coil submaster reference [CCSR]value) to satisfy conditions and outputs this value to the sub-master loop.OCCUPIED COOLINGGeneral — Economizer cycle must not be usable or damperposition must be open to 90% or higher.VAV Units — Supply fan must be ON for cooling control tooperate. Sequence is as follows:1. Unit must not be in Heating mode.2. Master Loop will survey occupancy status, Supply AirSet Point (SASP) and any Supply Air Temperature Resetcommand, then issue Cooling Coil Submaster Reference(CCSR) to Cooling Submaster Loop (CSL).3. The CSL surveys actual SAT, then calculates number ofcapacity stages required to produce the CCSR leaving theunit.4. Stages of cooling capacity are initiated. From zero stages,there will be a 1.5 to 3 minute delay before the first stageis initiated. The time delay between stages in increasingdemand is 90 seconds.39