404A PT CHART PDF
RA Pressure Temperature Chart. PRESSURE-TEMPERATURE CHART .. Refrigerants 22, a, A, and values are based on °F liquid temperature and the stated evaporator. PRESSURE-TEMPERATURE CHART .. Refrigerants 22, a, A, and values are based on °F liquid temperature and the stated.
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Figure 1 shows the usual starting set points to set up a LPC for various applications.
P T Chart 404a
Figure 8 is a chart for condensers with multiple fans. A differential setting of 5 psi to 10 psi will result in a reasonable cut-out setting of 8 to 13 psi. Note that when the solenoid valve is closed off the refrigerant is essentially trapped between the solenoid valve and the discharge valves of the compressor. If the beer cooler, used as previous example, were to use a pump-down system, the LPC cut-in setting would be determined as follows: For units located indoors, determine the lowest operating temperature of the unit.
Unless gauges are installed at the outlet of the evaporator and at the LPC connection to the system, not practicalthis D P can be estimated.
Remember—too close a differential may maintain close temperature control, but cause short cycling, greatly shortening equipment life.
Refrigerant Pressure – Temperature Chart
Avoid cut-out settings that result in a vacuum. For instance, a condenser with nine fans would have each fan cycling control turn three fans on and off at the same time. Too fhart a differential will cause short cycling of the condenser 404 and shorten the fan motor life. Set the differential at 11 psi. Set the cut-in at 31 psi. Allow 2 – 3 psi for suction line D P. Product Code Quantity 1 2 3 4 5. It is a good starting point.
These brief occasional cycles are not objectionable, but if they occur too often, are an indication of a leaky solenoid valve or leaky compressor valves. By cycling the compressor in response to the suction low side pressure, box temperature can be controlled.
The cut-out setting should be a reasonable amount of PSI lower than the cut-in, but not so low that the compressor will have difficulty reaching the cut-out setting. This will be the cut-in setting.
Very large condensers having four or more fans, usually have the fan cycling controls control two or more fans at a time. Refrigerant temperature is the design suction temperature when the compressor is on. An LP fan cycling control senses discharge head pressure and closes on rise of pressure.
The compressor will now go on at 33 psi and go off at psi suction pressure. Figure 7 shows suggested pressure settings for a single fan condenser.
Uses of Refrigeration Low Pressure Controls
Figure 3 is a guide for setting the LPC for outdoor units. The control opens on a fall in head pressure and shuts off the condenser fan, or fans. A 35 to 50 psi differential is suggested, depending on usage.
When the thermostat opens the circuit to the solenoid valve, the valve closes and the compressor pumps the refrigerant from the evaporator and suction line into the receiver and condenser, reducing the refrigerant pressure to the cut-out setting of the LPC and stops the compressor. Our example of a beer cooler could be set up as follows: For condensing cyart outdoors, either the coldest unit 440a temperature or the coldest ambient temperature selects the cut-in setting, whichever is the lowest temperature.
As box temperature decreases, the evaporator temperature decreases, and a lower suction pressure results.
Wiring is simplified and installed cost is reduced. Below that, flooded condenser valve systems should be used.
Uses of Refrigeration Low Pressure Controls | Industrial Controls
The differential is the difference between the cut-in and the cut-out pressures. Depending on how well the system balance was made, that is, matching the evaporator to the compressor capacity at the selected suction temperature, the compressor run time will be long enough to give good efficiency and not short cycle.
Set the cut-in at 18 psi.
Since these systems are small and usually closely coupled, the D P in the suction line should be somewhere around 2 to 4 psig. The LPC cut-in setting should be selected first.
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