Carrier 69NT20-531-300 manual Refrigeration Circuit 2.5.1 Standard Operation

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2.5 REFRIGERATION CIRCUIT 2.5.1 Standard Operation

Starting at the compressor, (see Figure 2-6, upper schematic) the suction gas is compressed to a higher pressure and temperature.

In the standard mode, both the economizer and unloader solenoid valves are closed. The gas flows through the discharge service valve into the oil separator. In the separator, oil is removed from the refrigerant and stored for return to the compressor when the oil return solenoid valve is opened by the controller. The oil return solenoid valve is a normally open valve which allows return of oil during the off cycle.

The refrigerant gas continues into the air-cooled condenser. When operating with the air-cooled condenser active, air flowing across the coil fins and tubes cools the gas to saturation temperature. By removing latent heat, the gas condenses to a high pressure/high temperature liquid and flows to the receiver which stores the additional charge necessary for low temperature operation.

When operating with the water cooled condenser active (see Figure 2-6, lower schematic), the refrigerant gas passes through the air cooled condenser and enters the water cooled condenser shell. The water flowing inside the tubing cools the gas to saturation temperature in the same manner as the air passing over the air cooled condenser. The refrigerant condenses on the outside of the tubes and exits as a high temperature liquid. The water cooled condenser also acts as a receiver, storing excess refrigerant.

The liquid refrigerant continues through the liquid line service valve, the filter-drier (which keeps refrigerant clean and dry) and the economizer (which is not active during standard operation) to the evaporator expansion valve. As the liquid refrigerant passes through the variable orifice of the expansion valve, some of it vaporizes into a gas (flash gas). Heat is absorbed from the return air by the balance of the liquid, causing it to vaporize in the evaporator coil. The vapor then flows through the suction modulation valve to the compressor.

The evaporator expansion valve is activated by the bulb strapped to the suction line near the evaporator outlet. The valve maintains a constant superheat at the coil outlet regardless of load conditions.

On systems fitted with a water pressure switch, the condenser fan will be off when there is sufficient pressure to open the switch. If water pressure drops below the switch cut out setting, the condenser fan will be automatically started. When operating a system fitted with a condenser fan switch, the condenser fan will be off when the switch is placed in the “O” position. The condenser fan will be on when the switch is placed in the “I” position.

2.5.2 Economized Operation

In the economized mode the frozen range and pull down capacity of the unit is increased by subcooling the liquid refrigerant entering the evaporator expansion valve. Overall efficiency is increased because the gas leaving the economizer enters the compressor at a higher pressure, therefore requiring less energy to compress it to the required condensing conditions.

During economized operation, flow of refrigerant through the main refrigerant system is identical to the standard mode. (The unloader solenoid valve is de-energized [closed] by the controller.)

Liquid refrigerant for use in the economizer circuit is taken from the main liquid line as it leaves the filter-drier (see Figure 2-7). The flow is activated when the controller energizes the economizer solenoid valve. The liquid refrigerant flows through the economizer expansion valve and the economizer internal passages absorbing heat from the liquid refrigerant flowing to the evaporator expansion valve. The resultant “medium” temperature/pressure gas enters the compressor at the economizer service valve.

2.5.3 Unloaded Operation

The system will operate in the unloaded mode during periods of low load, during periods of required discharge pressure or current limiting, and during start-up.

During unloaded operation, flow of refrigerant through the main refrigerant system is identical to the standard mode. (The economizer solenoid valve is de-energized [closed] by the controller.)

In the unloaded mode, a portion of the mid-stage compressed gas is bypassed to decrease compressor capacity. The flow is activated when the controller opens the unloader solenoid valve (see Figure 2-7. Opening of the valve creates a bypass from the economizer service valve through the unloader solenoid valve and into the suction line on the outlet side of the suction pressure modulation valve.

As load on the system decreases, the suction modulating valve decreases flow of refrigerant to the compressor. This action balances the compressor capacity with the load and prevents operation with low coil temperatures. In this mode of operation, the liquid injection solenoid valve will open as required to provide sufficient liquid refrigerant flow into the suction line for cooling of the compressor motor.

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T-309

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Contents Service Model Safety Summary 309 Safety-2 Safety-3 309 Table of Contents Table of Contents Check Controller Function Codes Connect Remote MonitoringPrecheck Procedure Checking The Stepper valve Valve ReplacementEvaporator Coil Replacement Evaporator Heater Replacement Replacing The Evaporator Fan AssemblyElectrical Wiring Schematic Refrigeration Circuit Schematic Economized Operation Refrigeration Circuit Schematic Standard OperationList of Tables DataCORDER Configuration VariablesUnit is fitted with a scroll compressor Section IntroductionManual, T-300 Section Description Evaporator Section Compressor Section Condenser Section Communications interface module For further information Module which allow communication with a masterOil level range, with the compressor off Model RSH105 Weight Dry 46.5 kg 103 lbTemperature Approved Oil Mobil ST32 Oil Charge 2957 ml 100 ouncesElectrical Data Safety and Protective Devices Refrigeration Circuit 2.5.1 Standard Operation Standard Operation with Receiver Refrigeration Circuit Schematic -- Economized Operation Section Microprocessor Temperature Control SystemKEY Function Controller Software Modes of Operation Perishable Mode -- Economy Controller Alarms Unit PRE-TRIP Diagnostics DCF02=6 Thermistor inputssupply & returnDCF02=2 DCF02=5 Usda thermistor inputsRaw Data Report for ABC1234567 Standard Configuration Download ReportLogging Interval dCF03 DataCORDER may be powered up in any one of four waysDataView DataCORDER Alarms SnAP CnF11 Defrost Off Selection NoOFFStd, Full CnF33 Snap Freeze OptionDisplay Only Functions Plicable with frozen set points Defrost temperature sensor reading is displayedPossibly delaying a needed defrost cycle Sensor ReadingController Function Codes Sheet 3 Controller Alarm Indications Sheet 1 Controller Alarm Indications Sheet 2 Controller Alarm Indications Sheet 3 Memory failure Error DescriptionOnds Draw test is done after 15 secondsP1-1 Draw test is done after 10 secondsCrease, the test fails Supply is comparedTest fails P6-2Requirements Control temperature must be at least 15.6C 60F Pressure switch is open or the condenser fan switch is openTimer is started Denser fan is started and a 60 second timer is startedBy starting P10-0 over Requirements Control temperature must be at least 7.2C 45FSet point, the test proceeds to test Inapplicable Functions Display Title Data 10 DataCORDER Alarm Indications 69NT Fresh AIR Makeup OperationTo start a pre-trip test, do the following Will be displayedWill be displayed Pull Down Falling Rising Controller Operation -- Perishable ModeController Operation -- Frozen Mode Frozen Mode Defrost Section Troubleshooting Unit will not heat or has insuffi Bent motor shaft Will not initiate defrostSuperheat Unit reads abnormal currents Current sensor wiring Check Valve Frontseated Backseated Section ServiceCompressor in a deep vacuum, internal dam- age will result Refrigerant Leak Checking Remove all refrigerant using a refrigerant recovery system Refrigerant Charge Compressor Upper Mounting Compressor OIL Level Condenser FAN and Motor Assembly Removing the Expansion Valve Two expansion valves are used, the evaporatorWrapped with Insulating compound. See Check superheat refer to step Cleaned regularly. The preferred cleaning fluid is freshIf applicable, braze the equalizer connection to Equalizer line14. Unloader Solenoid Valve Start unit and check operationEvaporator FAN Motor Capacitors Valve Override Controls Precheck Procedure TP1 Mounting Stud Type Cut one replacement sensor wire opposite color Cut wires 5 cm 2 inches from shoulder of defecCut one wire of existing cable 40 mm 1-1/2 inch Shorter than the other wireMaintenance of Painted Surfaces 23 Door Hinge Repair Crack, Chip & Hole Repair Kit 24. Insert Location In-lbs Ft-lbs 13.99 18.86 In-lbs #10 Ft-lbs 12.72 17.1414.6 49.4 37.08 12.3 41.6 31.25 32.8 24.64 22.7 17.00 11.9 Section Electrical Wiring Schematic Schematic Diagram Wiring Diagram Sheet 1 Wiring Diagram Sheet 2 Index 309 Index-2

69NT20-531-300 specifications

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