Carrier WeatherMaker 48A2020 Controls, Start-up, Operation, Service And Troubleshooting Instructions

46The Loadshed Group Number (SH.NM) corresponds to theloadshed supervisory device that resides elsewhere on the CCNnetwork and broadcasts loadshed and redline commands to itsassociated equipment parts. The SH.NM variable will default tozero which is an invalid group number. This allows the loadshedfunction to be disabled until configured.Upon reception of a redline command, the machine will be pre-vented from starting if it is not running. If it is running, thenDEM.L is set equal to the current running cooling capacity (RunStatusCOOLC.CAP).Upon reception of a loadshed command, the DEM.L variable isset to the current running cooling capacity (Run Status COOL  C.CAP) minus the configured Loadshed DemandDelta (SH.DL).A redline command or loadshed command will stay in effectuntil a Cancel redline or Cancel loadshed command is re-ceived, or until the configurable Maximum Loadshed time(SH.TM) has elapsed.HEAD PRESSURE CONTROLHead pressure refers to the refrigerant pressure at the dischargeside of the compressor. Thus it is sometimes refers to as “dis-charge pressure.” Head pressure control for will be managed di-rectly by the ComfortLink controls (no third party control).The head pressure control stages fixed speed fans and modulatingfans, if available, to maintain the head pressures of circuit A andcircuit B within acceptable ranges. For controls purpose, the headpressures are converted to saturated condensing temperatures(SCTs) as the feedback information to the condenser fans (also re-ferred to as “outdoor fans”). SCT.A is the saturated condensingtemperature for refrigeration Circuit A, and SCT.B is the saturatedcondensing temperature for refrigeration Circuit B. There are a to-tal of up to 6 condenser fans (depending on unit size and installedoptions) for controlling the head pressures of the 2 refrigerationcircuits, of which up to 3 fans can be controlled by each VFD(variable frequency drive) upon installation option.The control described in this document is also referred to ascondenser fan control. Where Greenspeed ® control is involved,it may also be referred to as low ambient control.The Greenspeed/low ambient or the factory-installed Motormastercontrol will be directly implemented in the ComfortLink soft-ware. It is not compatible with the field-installed Motormaster Vcontrol as found in CESR131343-07-xx and earlier software ver-sions that used an accessory with part numbersCRLOWAMB018A00 through CRLOWAMB026A00. Thesefield-installed accessory Motormaster V speed controls are com-pletely self-contained control units and are not controlled by theunit’s ComfortLink controller. On 48/50A 060 RTPF units with 6fan motors, the Motormaster control configuration (M.M.) mustbe set to YES for this field-installed option.Head Pressure Control OperationCondenser head pressure control for the 48/50A Series roof-tops is controlled discretely by the unit, except when the unit isequipped and configured for Greenspeed/low ambient or facto-ry-installed Motormaster Option control where head pressureswould be controlled via factory-installed VFDs. For a unit withthe factory-installed Motormaster option, the control would beable to cycle up to three stages of outdoor fans (see Table 49)to maintain acceptable head pressure.For 48/50A units, fan stages react to discharge pressure transduc-ers (DPT) (Pressures  REF.P  DP.A and DP.B) which areconnected to the compressor discharge piping in circuit A and B.The control converts the pressures to the corresponding saturatedcondensing temperatures (TemperaturesREF.TSCT.A andSCT.B).Unit size (ConfigurationUNITSIZE), refrigerant type(ConfigurationUNITRFG.T), and condenser heat ex-changer type (ConfigurationUNITCND.T) are used todetermine if the second stage fans are configured to respond toa particular refrigerant circuit (independent control) or both re-frigerant circuits (common control). The 48/50A 060 unitswith microchannel (MCHX) condenser heat exchangers are theonly units that utilize independent fan controls.If the unit is equipped with the optional Greenspeed / low ambi-ent control, the Outdoor VFD installed configuration (Configu-rationCOOLOV.EN) must be set to YES, to fully utilizehead pressure control function for optimal operations.The SCT.A and SCT.B sensors, which are connected to thecondenser coils in circuit A and B, will be used to measure thesaturated condensing temperature and may be used to controlhead pressure. The saturated condensing temperatures can beviewed in the TemperaturesREF.T submenu. The equiva-lent refrigerant pressure values, DP.A and DP.B, can be viewedunder the PressuresREF.P submenu.Head Pressure ConfigurationsThere are two configurations provided for head pressure con-trol that can be found at the local display based on the optionbeing installed in the factory:Configuration  COOL  OV.EN (Outdoor VFD Enabled)and ConfigurationCOOLLASP for units with Green-speed/low ambient optionConfigurationCOOLHPSP (Head Pressure Setpoint)Head Pressure OutputsThere are two condenser fan relays used to control head pres-sure for standard non-outdoor VFD option units:Condenser Fan A (OutputsFANSCD.F.A)Condenser Fan B (OutputsFANSCD.F.B)For units with Greenspeed/low ambient option, the head pres-sure would be controlled by the Outdoor Fan VFD A and B(OutputsFANSOV.A / OV.B).For units with factory installed Motormaster option, the headpressure would be controlled by the Motormaster VFD:MotorMastr Fan Circuit A (OutputsFANSMM.F.A)MotorMastr Fan Circuit B (OutputsFANSMM.F.B)MotorMastr Fan Command A (OutputsFANSA.VFD)MotorMastr Fan Command A (OutputsFANSB.VFD)Head Pressure AlgorithmThe following logic will describe the head pressure controlroutine when any compressor has been commanded on:• CD.F.A = ON• If the highest active circuit SCT is above the HPSP:CD.F.B = ON• If OAT is above 75°F: CD.F.A = ON and CD.F.B = ON(until OAT temperature drops below 73°F or the compres-sors are turned off)• If the SCT on an active circuit drops 20°F below the HPSPfor 2 minutes: CD.FB = OFF** For 60 ton size units not configured for Greenspeed/lowambient control or factory-installed Motormaster option,the control stages down differently than the other units.Because the condenser fan relays each turn on a differentnumber of outdoor fans, the control, when staging downwill first turn off condenser fan relay A and then in 2 moreminutes will turn off relay B and turn back on relay A.The details of fan staging are summarized in Fig. 8 and 9 foreach scenario.