Carrier AquaSnap 30MPA Series Controls, Start-up, Operation, Service, And Troubleshooting

Also see for AQUASNAP 30MPA: User manual Operation and service manual Installation instructions

Carrier AquaSnap 30MPA Series Controls, Start-up, Operation, Service, And Troubleshooting Manual pdf 17 page image

17Electronic Expansion Valves (EXV) — All30MP050-071 units are equipped from the factory with EXVs.The 30MPA and 30MPW units with medium brine tem-perature brine also have the EXV set at the factory to maintain9°F (5° C) suction superheat leaving the cooler by metering theproper amount of refrigerant into the cooler.The EXV is designed to limit the cooler saturated suctiontemperature to 50 F (12.8 C). This makes it possible for the unitto start at high cooler fluid temperatures without overloadingthe compressor.Capacity Control — Capacity control is determined bythe difference between the leaving fluid temperature and theControl Point (Run StatusVIEWCTPT) and its rate ofchange. The Control Point (CTPT) is the current set point mod-ified by a temperature reset command. This can be from thetemperature reset function or the dual chiller routine. The ca-pacity control routine runs every 30 seconds. The algorithm at-tempts to maintain the Control Point at the desired set point.Additionally, the control calculates a rise per stage knowingwhich compressor is on, its capacity and the temperature differ-ence across the cooler (entering fluid temperature minus leav-ing fluid temperature) to determine the best time to turn on oroff the next compressor, institute Minimum Load Control, orchange the digital response, if equipped. Entering and Leavingfluid temperatures can be monitored at the unit's interface de-vice Run StatusVIEWEWT and Run StatusVIEWLWT. With this information, a capacity ratio is calculated to de-termine whether to make any changes to the current stage ofcapacity. This ratio, Capacity Load/Unload Factor (Run Sta-tusVIEWLOD.F) value ranges from –100% to +100%times Deadband Multiplier (ConfigurationSLCTZ.GN).See Deadband Multiplier on this page for more information. Ifthe next stage of capacity is a compressor, the control starts(stops) a compressor when the ratio reaches +100% (–100%)times Deadband Multiplier (Z.GN). Once a change in capacityoccurs, a 90-second time delay is initiated and the capacitystage is held during this time delay.When the unit is at stage zero (Requested Stage Run Sta-tusVIEWSTGE=0) as part of the capacity control routine,the control adds a 1.2 factor on adding the first stage to reducecycling.If the unit is equipped with a digital compressor, it is nor-mally the first compressor started. If the lead compressor is adigital compressor, and is enabled and available (not in alarm),the compressor will start fully loaded for 90 seconds prior tostarting to cycle between loaded and unloaded. Once the digitalcompressor is on, positive changes in LOD.F will cause thecompressor to load. Negative changes to LOD.F will cause thecompressor to unload. This process can occur every 30 sec-onds. Changes to the digital loading are not subject to the 90-second delay. See Digital Scroll Option on page 36 for addi-tional information.If the unit is equipped with Minimum Load Control, it willnot be active until the unit is on its last stage of capacity. It toois treated as a stage of compression. As a result, MinimumLoad Control will be activated when capacity is decreasing,Requested Stage STGE=1, and Capacity Load/Unload FactorLOD.F= -100% times Deadband Multiplier (Z.GN). See Table14 for capacity step information.MINUTES LEFT FOR START — This value is displayedonly in the network display tables (using Service Tool,ComfortVIEW™ or ComfortWORKS™ software) andJ667REDBLKRED REDBLK BLKBLKREDBLKREDSENSOR 1 SENSOR 2 SENSOR 3 SENSOR 4J667REDBLKREDBLKSENSOR 2SENSOR 1REDREDBLKSENSOR 3SENSOR 4BLKBLKREDRED REDBLK BLKSENSOR 8 SENSOR 9SENSOR 5REDBLKSENSOR 6SENSOR 7BLKREDSPACE TEMPERATURE AVERAGING — 4 SENSOR APPLICATIONFig. 12 — Space Temperature AveragingLEGENDFactory WiringField WiringSPACE TEMPERATURE AVERAGING — 9 SENSOR APPLICATION