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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The pressure control for each fan should be set to cut-in about 10 psi apart.

Uses of Refrigeration Low Pressure Controls

It should be long enough to prevent short cycling, but not so long as to cause wide temperature variations or excessively low suction pressure, which may cause motor overheating or inadequate lubrication. 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.

The LPC cut-in setting should be selected first. Unless gauges are installed at the outlet of the evaporator and at the LPC connection to the system, not practicalthis D Chaart can be estimated.

Uses of Refrigeration Low Pressure Controls | Industrial Controls

For units located indoors, determine the lowest operating temperature of the unit. Very large condensers having four or more fans, usually have the fan cycling controls control two or more fans at a time. The final chosen differential has to be a compromise. Even low temperature freezers using R or RA should not be set lower than 0 psi cut-out.

Testing Wireless Solutions Testing wireless transmitters link. To control box temperature with a low-pressure control, the system must use a thermostatic expansion valve, non-bleed type.

Two settings need to be made on the LPC: Variations in systems will probably require small corrections of the settings. Figure 4 is typical of the piping for a pump-down system.


As an example for a beer cooler: Wiring is simplified and installed cost is reduced. Set the cut-in at 31 psi. The TD of the evaporator coil. Avoid cut-out settings that result in a vacuum. The refrigerant pressure increases, causing the LPC to cut-in, starting the compressor. It is a good starting point.

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. The differential is the difference between the cut-in and the cut-out pressures.

Allow 2 – 3 psi for suction line D P. Set the differential at 11 psi. The control opens on a fall in head pressure and shuts off the condenser fan, or fans. Product Code Quantity 1 2 3 4 5. Short cycling, due to door openings, etc. This type of control is most popular in small-refrigerated boxes such as beer coolers.

December 13, – 1: Figure 3 is a guide for setting the LPC for outdoor units. Remember—too close a differential may maintain close temperature control, but cause short cycling, greatly shortening equipment life.

Fine-tuning the differential setting should produce the desired results. If, during the off cycle, refrigerant leaks into the low side to raise the pressure to the LPC cut-in setting, the LPC will start the compressor for a short period until the pressure is lowered to the cut-out point and the compressor is once again stopped. Indoor unit, RA refrigerant. An LP fan cycling control senses discharge head pressure and closes on rise of pressure.

The same is not true for a standard temperature control. Set the cut-in at 18 psi.

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Figure 5 and Figure 6 show two of the more common wiring diagrams for pump-down systems. The settings in Figure 1 are only a beginning reference. A 35 to 50 psi differential is suggested, depending on usage. A differential setting of 5 psi to 10 tp will result in a reasonable cut-out setting cahrt 8 to 13 psi. Too small a differential will cause short cycling of the condenser fan and shorten the fan motor life. The compressor will now go on at 33 psi and go off at psi suction pressure.


Since we know the cut-in we want, this is easily determined.

The differential chosen will determine the compressor on time. Below that, flooded condenser valve systems should be used. The TD of the evaporator coil 3. This D P between the evaporator and the LPC connection will result in an increase in the differential setting. 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.

By cycling the compressor in response to the suction low 044a pressure, box temperature can be controlled. What all this means is that one picks cut-in and cut-out settings that should result in good temperature control, monitors the system, and then fine-tunes each specific job to achieve the desired results.

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. A wide differential will give longer running time, but may cause wide temperature swings. Figure 1 shows the usual starting set points to set up a LPC for various applications. For ;t units outdoors, either the coldest unit operating temperature or the coldest ambient temperature selects the cut-in setting, whichever is the lowest temperature.

TD is the temperature difference between the box temperature and the refrigerant temperature in the evaporator.