Carrier WeatherExpert 48N2 Controls, Start-up, Operation, Service And Troubleshooting Instructions

Also see for WeatherExpert 48N2: Installation instructions Installation instructions Controls, start-up, operation, service, and troubleshooting Installation instructions

Contents

Carrier WeatherExpert 48N2 Controls, Start-up, Operation, Service And Troubleshooting Instructions Manual pdf 61 page image

61When a condenser fan output is common to both refrigera-tion circuits, in other words when the fan(s) will affect both cir-cuit A and circuit B, the following logic is used: in order to adda fan stage, the SCT of either circuit must be above SCT.H for30 seconds and in order to subtract a stage, the SCT of both cir-cuits must be below SCT.L for 30 seconds.Whenever the outdoor ambient temperature (OAT), isabove 70 F, the maximum stage will always be on when thecompressors are on.On the initial start-up of a circuit, the condenser fans willstart 5 seconds prior to the compressor starting in order to en-sure proper head pressure of the compressor immediately atstart-up. After the compressor starts, the normal head pressureroutine will begin 30 seconds after the condenser fan pre-start.What stage fans starts depends on the outdoor ambient temper-ature. The three situations are:OAT < 50 F50 F < OAT < 70 FOAT > 70 FSee Fig. 10-13 for what stage of fans starts for eachscenario.ECONOMIZER INTEGRATION WITH MECHANICALCOOLING — When the economizer is able to provide freecooling (Run StatusECONACTV = YES), mechanicalcooling may be delayed or even held off indefinitely.NOTE: Once mechanical cooling has started, this delay logicis no longer relevant.Multi-Stage Cooling Economizer Mechanical CoolingDelay — This type of mechanical cooling delay is relevant tothe following machine control types:C.TYP = 1 VAV-RATC.TYP = 2 VAV-SPTC.TYP = 3 TSTAT-MULTIC.TYP = 4 SPT-MULTIIf the economizer is able to provide free cooling at the startof a cooling session, the mechanical cooling algorithm(SumZ), checks the economizer’s current position (Run StatusECONECn.P) and compares it to the economizer’smaximum position (ConfigurationECONEC.MX) – 5%.Once the economizer has opened beyond this point a 150 sec-ond timer starts. If the economizer stays beyond this point for2.5 minutes continuously, the mechanical cooling algorithm isallowed to start computing demand and stage compressors andunloaders.Heating Control — The N Series ComfortLink controlsoffers control for six different types of heating systems to satisfygeneral space heating requirements: 2-stage gas heat, 2-stageelectric heat, SCR (modulating) electric heat, steam heat, modu-lating gas heat, and hydronic heat. Heating control also providestempering and reheat functions. These functions are discussed inseparate sections. Reheat is discussed under Dehumidificationfunction on page 87.Variable air volume (VAV) type applications (C.TYP = 1 or2) require that the space terminal positions be commanded toopen to minimum heating positions when gas or electric heatsystems are active, to provide for the unit heating system’sMinimum Heating Airflow rate.Also, for VAV applications, the heat interlock relay (HIR)function provides the switching of a control signal intended foruse by the VAV terminals. This signal must be used tocommand the terminals to open to their Heating Open posi-tions. The HIR is energized whenever the Heating mode is ac-tive, an IAQ pre-occupied force is active, or if fire smokemodes, pressurization, or smoke purge modes are active.Hydronic and steam heating applications that use the unit’scontrol require the installation of a communicating actuator onthe hydronic heating coil’s control valve. This actuator (with orwithout matching control valve) may be separately shipped forfield installation.All heating systems are available as factory-installedoptions. The hydronic or steam heating coil may also be field-supplied and field-installed; the actuator is still required if unitcontrol will be used to manage this heating sequence.POST FILTER APPLICATION — Gas heat controls also usean airflow switch when post filter option is installed in unit.Lack of airflow will prevent gas heat from operating.Electric heat controls add filter temperature switches at thepost filters. The filter temperature switches will prevent electricheat from operating when high temperatures are experienced.SETTING UP THE SYSTEM — The essential heating con-figurations located at the local display under ConfigurationHEAT. See Table 34.Heating Control Type (HT.CF) — The heating control typesavailable are selected/configured with this variable.0 = No Heat1 = 2 Stage Electric Heat2 = 2 Stage Gas Heat3 = Staged Gas Heat or Modulating Gas Heat4 = Hydronic Heat (Hot Water or Steam)5 = SCR Electric HeatHeating Supply Air Set Point (HT.SP) — In a low heat modefor either modulating gas, SCR electric, or hydronic heat, thisis 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.