Carrier 48/50PG C03-14 Operation And Service Manual

Contents

21Heating OperationThe 48/50PG and 48/50PM unit’s heating operation consists of:demand, mode determination, staging request to satisfy thedemand, and handling a request with the unit’s resources. Theseresources can be gas heat or electric heat. This section covers bothgas heat units and electric heat units. The Type of Heat Installed(Configuration→HEAT→HT.TY) configuration will be factoryset to 1 for gas units, 2 for electric heat units with heaters installed,and 0 for electric heat units without heat installed. The unit entersa heating mode based on a demand, decides how to satisfy thedemand, executes its plan, and then leaves the heating mode.Heating Mode ControlThe heating HVAC mode (Run Status→MODE→HVAC=4),represents both types of heating (gas or electric) under all types ofcontrol. For the unit to be allowed to enter the heat mode, heatmust be enabled (HT.TY = 1 or 2), and the Outdoor AirTemperature (Temperatures→AIR.T→OAT) must be less than theHeating Lockout Temp (Configuration→HEAT→HT.LO). HeatOAT Lockout (Run Status→MODE→H.LOC) displays whenheat is locked out on outdoor temperature and therefore can notallow heat mode. The control will display if it is ok to select theheating mode (Operating Modes→HEAT →OK.HT= Yes).Thermostat ControlFor the unit to enter heating mode, three additional things must betrue: the indoor fan must be ok to use, the mode changeover timeguard must be expired, and there must be a heating demand (W1,W2). The unit will remain in heating until the heating demand isdropped or if any of the above conditions turn false. The heatingmode can not officially end until all heat stages are off and the IGCfan request is dropped (on gas units without Humidi−MiZer).Space Sensor ControlFor the unit to enter heating mode, five additional things must betrue: the indoor fan must be ok to use, the mode changeover timeguard must be expired, the unit must have a valid spacetemperature, the W1 jumper must be installed, and there must be aheating demand. The unit will remain in heating for at least oneminute and until the heat demand drops below −0.5F or if any ofthe above conditions turn false. The heating mode can notofficially end until all heat stages are off and the IGC fan request isdropped (on gas units without Humidi−MiZer).Supply−Air Temperature Sensor (SAT)The SAT Heat Mode Sensing (Configuration→HEAT→SAT→SAT.H) informs the unit if the supply air sensorhas been relocated downstream of the heat section. Thisconfiguration affects the Supply Air Temperature (Temperatures→AIR.T→SAT) value displayed as listed below.When SAT.H = DSBL, the Supply Air Temperature (Temperatures→AIR.T→SAT) value on the Scrolling Marquee and the CCNtables will be forced to zero when heat outputs turn ON or OFFand for 5 minutes after. The default Supply Air Temperaturelocation is at the fan inlet, upstream of the heat section.When SAT.H = ENBL, the Supply Air Temperature (Temperatures→AIR.T→SAT) sensor reading is displayed at the ScrollingMarquee and the CCN tables during heating mode. This settingshould only be used if the original SAT sensor wires are removedfrom the Main Base Board (MBB) and replaced by an accessorySAT sensor located in the supply duct downstream of theheat section.There are two supply air temperature limits that affect heatingoperation, the Maximum SAT Lower Level (Configuration→HEAT→SAT→SAM.L) the Maximum SAT Upper Level(Configuration→HEAT→SAT→SAM.U). Any time the supplyair temperature rises above SAM.L the heat staging will be limitedto what is currently on and no additional stages can be added untilthe supply air temperature falls back below SAM.L. If the supplyair temperature rises above SAM.U, then heating will be reducedby removing a heat stage. That stage can not be added again untilthe Supply Air Temperature falls below SAM.L. If the supply airtemperature stays above SAM.U, then another stage will beremoved after the Heat Stage Decrease Time (Configuration→HEAT→H.DEC). If SAM.L and SAM.U are configured so thatthey are close together, the last stage of heat might cycle rapidly,slowed only by its minimum on and off−time requirements.Staging ControlOnce the unit is in a heating mode, it must decide what the demandis and how to satisfy. Based on the unit control configuration,requested heating stages (Run Status→HEAT→REQ.H) will bedetermined then passed to heat control to actually add the heatingstages.Thermostat ControlThere are two ways of requesting stages when thermostat control isenabled: Traditional Thermostat control or Adaptive control.Traditional Thermostat control is used if the Thermostat ControlType (T.CTL) is set to 1, 2, or 3. Adaptive control is used ifThermostat Control (T.CTL) is set for 0.T.CTL = 0 (Adaptive Control)Stage timers and supply air temperature limits apply whendetermining the request for stages. The first request (REQ.C=1)comes immediately when the W1 input is active. The Heat StageIncrease Time (Configuration→HEAT→H.INC) or the HeatStage Decrease Time (Configuration→HEAT→H.DEC) has toexpire before another stage can be added or a stage can besubtracted. If at any time the Supply−Air Temperature (SAT) risesabove the Maximum Supply Air Temperature Lower Level(Configuration→HEAT→SAT→SAM.L), the requested stageswill not be allowed to increase. If at any time the SAT rises abovethe Maximum Supply Air Temperature Upper Level(Configuration→HEAT→SAT→SAM.U), the requested stageswill be reduced by one without honoring H.DEC.T.CTL = 1, 2 or 3 (Traditional thermostat control)Stage timers and supply air temperature limits do not apply whendetermining the request for stages. Request staging will follow thethermostat inputs directly. W1 will request one stage. W2 willrequest all stages.48/50PG and PM