Carrier 48HC 04-28 Controls, Start-up, Operation And Troubleshooting

Also see for /50HC 04-28: Manual

Contents

Carrier 48HC 04-28 Controls, Start-up, Operation And Troubleshooting Manual pdf 21 page image

21cooling demand drops below -0.5°F or if any of the above con-ditions turn false. If only a dehumidification demand exists andthe heat demand becomes greater than the Reheat Heat Set-point Deadband (SetpointsRH.HB), the unit will end cool-ing. The cooling mode can not officially end until all compres-sors are off.STAGING CONTROLOnce the unit is in a cooling mode, it must decide what the de-mand is and how to satisfy it. If an economizer is installed andcan be used for cooling (Operating ModesCOOLOK.EC=Yes), the unit will use it first (see economizer section for its oper-ation). If the economizer can not be used or additional cooling isneeded, a mechanical cooling check is performed. OK to useCompressors? (Operating ModesCOOLOK.MC), will beset to yes when compressors are enabled and not locked out.Based on the unit control configuration, requested cooling stages(Run StatusCOOLREQ.C) will be determined then passedto compressor control to actually add the cooling stages.Thermostat ControlThere are two ways of requesting stages when thermostat con-trol is enabled, Traditional Thermostat control or Adaptivecontrol. Traditional Thermostat control is used if the Thermo-stat Control Type (T.CTL) is set to 1, 2, or 3 and the economiz-er is not available for free cooling. If Thermostat Control(T.CTL) is set to 0 or any time the economizer is available forfree cooling, the unit will use Adaptive control for staging.T.CTL = 0 (Adaptive Control)Stage timers, Supply air trend, and supply air temperature lim-its apply when determining the request for stages. The first re-quest (REQ.C=1) comes immediately when the Y1 input is ac-tive. The Cool Stage Increase Time (Configura-tionCOOLC.INC) or the Cool Stage Decrease Time(ConfigurationCOOLC.DEC) has to expire before anoth-er stage can be added or a stage can be subtracted. The Supply-Air Trend (Operating ModesCOOLSA.TR) decides if thenext stage can be requested or should be subtracted based onthe Y2 input status. If the Y1 and Y2 inputs are dropped, thesupply air trend is not considered because cooling is no longerneeded. If at any time the Supply-Air Temperature (SAT) fallsbelow the Minimum Supply Air Temperature Upper Level(ConfigurationCOOLSATSAT.U), the requested stageswill not be allowed to increase. If at any time the SAT falls be-low the Minimum Supply Air Temperature Lower Level (Con-figurationCOOLSATSAT.L), the requested stages willbe reduced by one without honoring C.DEC. If SAT.L andSAT.U are configured so that they are close together, the laststage of compressor might cycle rapidly, slowed only by itsminimum on and off-time requirements.T.CTL = 1 (1 Stage Y1) and T.CTL = 2 (2 Stage Y1)Stage timers, Supply air trend, and supply air temperature lim-its do not apply when determining the request for stages. Re-quest staging will follow the thermostat inputs directly. Y1 willrequest one stage. Y2 will request all stages.T.CTL = 3 (Digital)Stage timers, Supply air trend, and supply air temperature lim-its do not apply when determining the request for stages. Re-quest staging will follow the thermostat inputs directly. Y1 willrequest one stage. Y2 will request two stages. Y1 and Y2 willrequest all stages.Space Sensor ControlSpace sensor staging control is an adaptive anticipation controlthat weighs the actual space demand against the trend of thatdemand and the trend of the supply air. It also honors stagetime guards and supply air limits. The demand for cooling inthe space is displayed as the Cooling Demand (Run Sta-tusCOOLDMD.C). The control tries to anticipate thechange in the space because of its current stage status. This an-ticipation is based on the Supply-Air Trend (OperatingModesCOOLSA.TR) and the Cool Demand Trend (Oper-ating ModesCOOLTRD.C). These trends will show thecontrol how the space is reacting to the current running condi-tions and help it decide when to add or remove one stage fromthe requested stages. The Cool Stage Increase Time (Configu-rationCOOLC.INC) or the Cool Stage Decrease Time(ConfigurationCOOLC.DEC) has to expire before anoth-er stage can be added or a stage can be subtracted. If at anytime the Supply-Air Temperature (SAT) falls below the Mini-mum Supply Air Temperature Upper Level (Configura-tionCOOLSATSAT.U), the requested stages will not beallowed to increase. If at any time the SAT falls below the Min-imum Supply Air Temperature Lower Level (Configura-tionCOOLSATSAT.L), the requested stages will be re-duced by one without honoring C.DEC. If SAT.L and SAT.Uare configured so that they are close together, the last stage ofcompressor might cycle rapidly, slowed only by its minimumon and off-time requirements.COMPRESSOR CONTROLThe compressor control works hand and hand with the stagingcontrol. As the staging control requests stages, the compressorcontrol determines what actual compressors are available orrunning and tries to provide stages for what is requested. Theavailability of a compressor depends on time guards, circuit di-agnostics, outdoor temperature, and the unit size.The Number of Circuits (ConfigurationCOOLN.CIR)configuration tells the control how many compressors are in-stalled on the unit. The Circuit A Lockout Temp (Configura-tionCOOLCIR.ACA.LO) and Circuit B Lockout Temp(ConfigurationCOOLCIR.BCB.LO) configurations setthe outdoor temperature in which the respective compressor isallowed to run down to. Timeguard A (Run Sta-tusCOOLCIR.ATG.A) and Timeguard B (Run Sta-tusCOOLCIR.BTG.B) display the time a respectivecompressor has before it is available for use. Individual circuitdiagnostic tests are performed during operation which may ormay not allow a compressor to be used. The available stages atany given time are displayed as Available Compressors (RunStatusCOOLAVL.C). The actual compressors running atany given time are displayed as Actual Cooling Stages (Oper-ating ModesCOOLACT.C). Compressor A (Run Sta-tusCOOLCIR.ACMP.A) and Compressor B (Run Sta-tusCOOLCIR.BCMP.B) are displayed on when the re-spective compressor is running.There are time guards to protect the compressors. CompressorMin On Time (ConfigurationCOOLMRT.C) and Com-pressor Min Off Time (ConfigurationCOOLMOT.C) ap-ply before a compressor can be turned back on or turned off.OUTDOOR FAN CONTROLOutdoor fans are controlled electro-mechanically, not directlyby the control system. Refer to specific unit wiring diagramand or service manual for details on how the outdoor fans oper-ate. In general, the outdoor fan is energized with compressor Aor may have partial fans operate with compressor B. Humidi-MiZer units will have a Motormaster control on some or allfans.Heating OperationThe 48/50HC unit’s heating operation consists of: demand,mode determination, staging request to satisfy the demand, andhandling a request with the unit’s resources. These resourcescan be gas heat or electric heat. This section covers both gasheat units and electric heat units. The Type of Heat Installed(ConfigurationHEATHT.TY) configuration will be facto-ry set to 1 for gas units, 2 for electric heat units with heaters in-stalled, and 0 for electric heat units without heat installed. Theunit enters a heating mode based on a demand, decides how tosatisfy the demand, executes its plan, and then leaves the heat-ing mode.