Carrier 48AJ Operating And Service Manual

Also see for 48AJ: Installation, Start-Up and Service Instructions Installation instructions Operation and service guide Started guide

48Heating Control Type (HT.CF) — The heating control typesavailable are selected/configured with this variable.0 = No Heat1 = Electric Heat2 = 2 Stage Gas Heat3 = Staged Gas HeatHeating Supply Air Set Point (HT.SP) — In a low heat modefor staged gas heat, this is the supply air set point for heating.Occupied Heating Enable (OC.EN) — This configurationonly applies when the unit’s control type (Configuration→UNIT→C.TYP) is configured for 1 (VAV-RAT) or 2 (VAV-SPT). If the user wants to have the capability of performingheating throughout the entire occupied period, then thisconfiguration needs to be set to “YES”. Most installations donot require this capability, and if heating is installed, it is usedto heat the building up in the morning. In this case set OC.ENto “NO”.NOTE: This unit des not support simultaneous heating andcooling. If significant simultaneous heating and coolingdemand is expected, it may be necessary to provide additionalheating or cooling equipment and a control system to provideoccupants with proper comfort.MBB Sensor Heat Relocate (LAT.M) — This option allowsthe user additional performance benefit when under CCNLinkage for the 2-stage electric and gas heating types. As two-stage heating types do not “modulate” to a supply air set point,no leaving air thermistor is required and none is provided. Theevaporator discharge thermistor, which is initially installed up-stream of the heater, can be repositioned downstream and thecontrol can expect to sense this heat. While the control does notneed this to energize stages of heat, the control can wait for asufficient temperature rise before announcing a heating modeto a CCN Linkage system (ComfortID™).If the sensor is relocated, the user will now have thecapability to view the leaving-air temperature at all times atTemperatures→AIR.T→CTRL→LAT.NOTE: If the user does not relocate this sensor for the 2-stageelectric or gas heating types and is under CCN Linkage, thenthe control will send a heating mode (if present) uncondition-ally to the linkage coordinator in the CCN zoning systemregardless of the leaving-air temperature.Fan-Off Delay, Gas Heat (G.FOD) — This configuration isthe delay in seconds, after a gas heat mode has ended(HT.CF=2,3) that the control will continue to energize thesupply fun.Fan-Off Delay, Elec Heat (E.FOD) — This configuration isthe delay in seconds, after an electric heat mode has ended(HT.CF=1) that the control will continue to energize thesupply fun.HEAT MODE SELECTION PROCESS — There are twopossible heat modes that the control will call out for heatingcontrol: HVAC Mode = LOW HEAT and HVAC Mode =HIGH HEAT. These modes will be called out based on controltype (C.TYP).VAV-RAT (C.TYP = 1) and VAV-SPT (C.TYP = 2) — Thereis no difference in the selection of a heating mode for eitherVAV-RAT or VAV-SPT, except that for VAV-SPT, space tem-perature is used in the unoccupied period to turn on the supplyfan for 10 minutes before checking return-air temperature. Theactual selection of a heat mode, LOW or HIGH for bothcontrol types, will be based upon the controlling return-airtemperature.With sufficient heating demand, there are still conditionsthat will prevent the unit from selecting a heat mode. First, theunit must be configured for a heat type (Configuration→HEAT→HT.CF not equal to “NONE”). Second, the unit has aconfiguration which can enable or disable heating in theoccupied period except for a standard morning warmup cycle(Configuration→HEAT→OC.EN). See descriptions above inthe Setting Up the System section for more information.If the unit is allowed to select a heat mode, then the nextstep is an evaluation of demand versus set point. At this point,the logic is the same as for control types SPT Multi-Stage andSPT-2 Stage, (C.TYP = 5,6) except for the actual temperaturecompared against set point. See Temperature Driven HeatMode Evaluation section.Tstat-Multi-Stage (C.TYP = 3) and Tstat-2 Stage (C.TYP =4) — There is no difference to consider for selecting a heatmode whether the control type is for TSTAT 2-stage or TSTATmulti-stage as this only refers to how cooling will be handled.With thermostat control the W1 and W2 inputs determinewhether the HVAC Mode is LOW or HIGH HEAT.W1 = ON, W2 = OFF: HVAC MODE = LOW HEAT*W2 = ON, W2 = ON: HVAC MODE = HIGH HEAT*If the heating type is either 2-stage electric or 2-stage gas, theunit may promote a low heat mode to a high heat mode.NOTE: If W2 = ON and W1 is OFF, a “HIGH HEAT” HVACMode will be called out but an alert (T422) will be generated.See Alarms and Alerts section on page 86.SPT Multi-Stage (C.TYP = 5) and SPT 2 Stage (C.TYP = 6)— There is no difference to consider for selecting a heat modewhether the control type is for SPT 2-stage or SPT multi-stage asthis only refers to how cooling will be handled. So, for a validheating type selected (HT.CF not equal to zero) the unit is freeto select a heating mode based on space temperature (SPT).If the unit is allowed to select a heat mode, then the nextstep is an evaluation of demand versus set point. At this point,the logic is the same as for control types VAV-RAT andVAV-SPT (C.TYP = 1,2), except for the actual temperaturecompared against set point. See Temperature Driven HeatMode Evaluation section below.TEMPERATURE DRIVEN HEAT MODE EVALUATION —This section discusses the technique for selecting a heatingmode based on temperature. Regardless of whether the unit isconfigured for return air or space temperature the logic is ex-actly the same. For the rest of this discussion, the temperaturein question will be referred to as the “controlling temperature.”First, the occupied and unoccupied heating set points underSetpoints must be configured.Then, the heat/cool set point offsets under Configuration→D.LV.T should be set. See Table 60.Related operating modes are under Operating Modes→MODE.The first thing the control determines is whether the unitis in the occupied mode (OCC) or in the temperature compen-sated start mode (T.C.ST). If the unit is occupied or in tempera-ture compensated start mode, the occupied heating set point(OHSP) is used. In all other cases, the unoccupied heatingsetpoint (UHSP) is used.The control will call out a low or high heat mode bycomparing the controlling temperature to the heating set pointand the heating set point offset. The set point offsets are used asadditional help in customizing and tweaking comfort into thebuilding space.ITEM EXPANSION RANGE UNITS CCNPOINT DEFAULTOHSP Occupied HeatSetpoint 55-80 dF OHSP 68UHSP UnoccupiedHeat Setpoint 40-80 dF UHSP 55ITEM EXPANSION RANGE CCN POINTMODE MODES CONTROLLING UNITOCC Currently Occupied ON/OFF MODEOCCPT.C.ST Temp.Compensated Start ON/OFF MODETCST