Carrier Infinity 24VNA6 Series Service Manual

Also see for Infinity 24VNA6: Installation instructions Owner's manual

24VNA6 / 25VNA4: Service ManualManufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.9CONTROL FEATURES AND OPERATIONEquipment Configuration (Model Plug)The PCM detects the model plug value at power-up and configuresoperation of the equipment to the model identification specified by themodel plug for the remainder of the power cycle. Model plugdiagnostics will occur while the equipment is operating, but changes to amodel plug will not affect equipment operation until power is cycled.The PCM remembers the most recent valid model plug detected atpower-up. If a model plug is lost or missing during equipmentoperation, the PCM will continue to operate the equipment based on themost recent valid model plug detected at power-up. Model plug memoryis preserved across power cycles, so if a model plug becomes missing,proper equipment operation will continue even if power to theequipment is lost and then restored.An installed model plug at power-up takes precedence over a model plugvalue stored in memory. If a new valid model plug value is detected atpower-up, the model plug memory will be updated to that new value.Performance ModeThe PCM supports equipment operation in two performance modes:Efficiency and Comfort. Efficiency mode provides maximum possibleoperating efficiency. Comfort mode modifies operation to provideoptimal comfort to the home.Compressor OperationCompressor Protect DelayThe compressor is inhibited from running within 5 minutes of powerbeing applied to the equipment or within 5 minutes of previousoperation. The Compressor Protect Delay can be overridden as describedin Overrides in the Troubleshooting section.StartingThe compressor will not start if the differential pressure between suctionand discharge is greater than 100 psi. When a capacity demand isreceived, the outdoor fan begins operating first. Once the fan beginsoperating, the compressor is started. The compressor will ramp to 2,700rpm and dwell at that speed until the required amount of discharge superheat is developed.RunningOnce start-up super heat is reached, the compressor will ramp up ordown to the appropriate continuous operating speed. Compressoroperating speed depends on the capacity being requested by the InfinityControl, the Operating Mode (Cooling vs. Heating), the outdoor airtemperature, and the Performance Mode setting.Compressor Reliability ProtectionDuring operation, the PCM monitors the operating point of thecompressor relative to the reliability operating envelope. If operationattempts to exceed a reliability limit, system operation is modified tobring operation back within the envelope. Examples of modifiedoperation include increasing fan speed and reducing compressor speed.During extreme operating conditions, operation may not be able to bemaintained within the reliability envelope. If this occurs, the PCM willshut down the system and set a diagnostic code indicating the type oflimit being exceeded. Extreme operating conditions are usually partiallyor completely created by non-ideal operating conditions that can becorrected by equipment service. Examples of such conditions includeblocked or partially blocked coil on the indoor or outdoor equipment,and under-charged or over-charged systems.Sump HeatWhen the compressor is not running, the compressor sump may need tobe heated to prevent liquid refrigerant from collecting in the sump. Thiscondition is most likely with reduced outdoor temperatures.Some systems use an external Crankcase Heater installed around thebottom portion of the compressor. Other systems may use a statorheating function where the VFD flows a DC current through the motorwindings. This stator current heats the motor. That heat is transferred tothe compressor shell and heats the compressor sump.Fan OperationThe fan generally runs when the compressor is running. When theequipment begins to operate, the fan will start first, then the compressorwill start. Fan speed is adjusted based on the Operating Mode (Coolingvs. Heating), the outdoor air temperature and compressor speed.Intermittent Low Fan SpeedIn some operating conditions such as Low Ambient Cooling, airflowrequirements are below the minimum fan speed. In these cases, the fanwill operate intermittently. The fan on/off cycle during this operation isapproximately 40 seconds.Fan Operating ExceptionsThere are some operating conditions where the fan will operateindependently of the compressor. During the defrost cycle, the fan willnot operate while the compressor is running. It is possible for theequipment to shut down during a defrost cycle. On the next operatingcycle, the equipment will resume in defrost mode. In this case, the fanwill run briefly at power-up and then shut down while the previouslyinterrupted defrost cycle completes.The fan may intermittently shut down during Low Ambient Coolingoperation, especially at colder temperatures and if the wind is blowingduring operation.If the compressor is shut down due to a discharge pressure limit or VFDor compressor high discharge temperature limit, the fan will continue torun for a period of time after the compressor shuts down in order toalleviate the excessive temperature or pressure condition.Cooling ControlCooling mode will operate at any outdoor ambient temperature of 55°F(12.78°C) or higher. There is no upper limit of outdoor ambienttemperature operation. Full cooling capacity is available up to at least125°F (51.67°C) for properly installed and maintained equipment. IfLow Ambient Cooling is enabled on the Infinity Control, the coolingmode will operate down to 0°F (-17.78°C).Heating Control(25VNA4 Only)Heating mode will operate up to an outdoor ambient temperature of 75°F(23.9°C). Heating mode will start down to 0°F (-17.78°C). If theequipment is already operating when ambient temperature drops below0°F (-17.78°C), the equipment will continue to operate until some limitis reached. Heating capability should be available down to -10°F(-23.3°C) or lower for properly installed and maintained equipment.Super Heat ControlSuper heat control is provided by the EXV-H. The PCM continuouslyadjusts the EXV-H to keep suction super heat operating at the targetcontrol value.Defrost Mode(25VNA4 Only)Defrost mode is part of Heating Control. Because the outdoor coiloperates at a temperature below ambient, it has the potential forcondensing moisture from the air. When the coil temperature is atfreezing conditions, that condensation will occur as frost. As frost buildson the coil, the frost acts as an insulator and reduces the heating capacityof the coil. Periodic defrost is required to remove frost and restoreheating capacity.