Carrier 48LC Series Controls, Start-up, Operation And Troubleshooting

Also see for 48LC 05: Controls, Start-Up, Operation and Troubleshooting Service and maintenance instructions Service and maintenance instructions

Contents

Carrier 48LC Series Controls, Start-up, Operation And Troubleshooting Manual pdf 17 page image

17Indoor (Supply) Fan Maximum Speed(MAXIMUM IDF SPEED)Max speed is the highest fan speed allowed. This is typically 100%when pulleys are set to deliver design CFM to the space per jobrequirement. Most safety conditions for the unit will override thefan speed to this to help protect the unit.Ventilation Indoor Fan Speed (VENT IDF SPEED)This configuration defines the fan speed used in Ventilation(fan--only) mode. Ventilation mode is when the supply fan isrunning, but there is no demand for heating or cooling. Inthermostat mode, this is with just a G call. In space sensor control,this is when the unit is Occupied mode and the indoor fan isconfigured to always run while occupied (OCCUPIED FAN?). Ifthe indoor fan is configured for intermittent fan (OCCUPIEDFAN? = No), the Mode will be off instead of Ventilation and thefan will not run unless a heating or cooling mode is needed. Duringthe unoccupied period, the fan will always operate intermittently.The economizer damper will adjust its position based on how faraway this speed is from max speed for ventilation.IMPORTANT: It is important that the ventilation rate is checked aftersetting this speed to verify that the unit can properly ventilate the spaceper requirements. Adjusting this configuration or the economizerminimum setting curve should be performed to meet job requirements.Heating Indoor Fan Speed (HEATING IDF SPD)This configuration defines the fan speed used when in heatingmode and running heat. On units equipped with Gas heat (UNITTYPE OF HEAT), this heat speed will be delayed on based on theIGC’s fan on call (IGC FAN REQUEST). Once the IGC requestthe fan the fan will run what this heating speed configuration is setfor until heating is ended. On units configured for Electric heat(UNIT TYPE OF HEAT) and configured for Preheat without thefan (PREHEAT W/O IDF), this heat speed will be delayed onbased on the Preheat fan delay time (PREHEAT FAN DELAY).Once this preheat time has expired or not configured for preheat,the fan will run at this heat speed while heat is on.Free Cooling Indoor Fan Speed (FREE COOL IDF SPD)This configuration defines the initial fan speed used when in FreeCooling. Refer to the Economizer Controls Operation section fordetails on free cooling. The fan will stay at this configured speedwhenever only the damper is being used for free cooling. If thedamper is at 100% for 5 minutes the fan will ramp to the highcooling speed. It is locked there until the actual damper positionfalls below 75% at which time it will ramp back down to thisconfigured speed.Low Cooling Indoor Fan Speed (LOW COOL IDF SPD)This configuration defines the fan speed used when only one stagemechanical cooling is being performed.Medium Cooling Indoor Fan Speed (MED COOL IDF SPD)This configuration defines the fan speed used when only secondstage mechanical cooling is being performed.High Cooling Indoor Fan Speed (HIGH COOL IDF SPD)This configuration defines the fan speed used when third (full load)stage mechanical cooling is being performed. When performingintegrated cooling with the economizer this speed will be used. Whenonly free cooling with a high cool demand, this speed will be used.Cooling OperationThe 48/50LC unit’s cooling operation consists of: demand andmode determination, staging request to satisfy the demand, andhandling a request with the unit’s resources. These resources caninclude compressors, Humidi--MiZerR system, an economizer, andfan speed based on options. This section covers mechanicalcooling. For economizer free cooling, refer to the EconomizerOperation section (starting on page 24).For Humidi--MiZer system operation, refer to the OptionalHumidi--MiZer Dehumidification System section (see page 19).Cooling Mode ControlThe cooling HVAC mode (OPERATING MODE) has 9 differentoperating sub modes (SUBMODE): ECON FREE COOLING,UNOCC. FREE COOL, MECH. COOLING, ECON/MECHCOOLING, DEHUMIDIFICATION, DEHUM/MECH COOLING,DEHUM PREVENTED, COOLING PREVENTED, andSHUTTING COOL OFF. These are all part of a general coolingmode and resemble the specific type of cooling that is beingperformed at any given time. All types of cooling are still performedunder the general cooling function, and the expanded text is for userreference only.For the unit to enter cooling mode, three things must be true: theindoor fan must be ok to use, the mode changeover time guard mustbe expired, and there must be a cooling or dehumidification demand(Y1, Y2, Y3, space cool demand, or humidity demand). The unit willremain in cooling for at least one minute or until any of the aboveconditions turn false. The cooling mode does not officially end untilthe compressor is off and the fan off delay has expired.Cooling Staging ControlOnce the unit is in a cooling mode, determine what the demand isand how to satisfy it. If an economizer is installed and can be usedfor cooling (OK TO USE FREE COOLING? = Yes), the unit willuse it first (see economizer section for its operation). If theeconomizer cannot be used or additional cooling is needed, amechanical cooling check is performed. OK to use Compressors?(OK TO USE COMPS?) will be set to yes when the outdoortemperature (OUTDOOR AIR TEMP) is above the Circuit ALockout temperature (CIR.A LOCKOUT OAT) and the Circuit Ais not locked out for diagnostic reasons (CIRCUIT A LOCKOUT).Based on the unit control configuration, requested cooling stages(REQ. COOL STAGES) will be determined then passed tocompressor control to actually add the cooling stages.There are two ways of requesting stages when thermostat control isenabled, Traditional thermostat control or adaptive control.Traditional thermostat control is used if set for non--adaptivethermostat (ADAPTIVE TSTAT = NO) and the unit cannot use theeconomizer for free cooling. If set for adaptive thermostat(ADAPTIVE TSTAT = YES) or any time the economizer isavailable for free cooling, the unit will use adaptive control forstaging.When configured for Space sensor or RAT control (UNITCONTOL TYPE) the unit will use adaptive control for staging.With either staging method there are two supply air temperaturelimits that apply, one restricts more cooling stages and the otherwill remove cooling stages. If at any time the Supply--AirTemperature (SUPPLY AIR TEMP) falls below the MinimumSupply Air Temperature Upper Level (UPPER MIN SAT), therequested stages will not be allowed to increase. If at any time theSAT falls below the Minimum Supply Air Temperature LowerLevel (LOWER MIN SAT), the requested stages will be reducedby one. If these SAT limits are configured so that they are too closetogether, the last stage might cycle rapidly, slowed only by itsminimum on and off--time requirements.Adaptive ControlStage timers and Supply air trend apply when determining therequest for stages. The first request (REQ. COOL STAGES =1)comes immediately when starting the staging process. The CoolStage Increase Time (COOL STAGEUP TIME) has to expire andthe Supply--Air Trend (SUPPLY AIR TREND) has to be abovethe cooling supply air trend level (COOL SATTREND LEV)before another stage can be added. Requested stages will only beallowed to increase as the actual system demand allows(DEMAND). A “LOW COOL” demand will only allow onerequested stage, “MED COOL” two stages, and “HIGH COOL” 3stages. The requested stages will be reduced if the cooling demandis lowered or dropped completely, or if the supply air falls belowthe lower level (LOWER MIN SAT).