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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In a pump down system, a thermostat controls a solenoid valve in the liquid line. Too small a differential will cause short cycling of the condenser fan and shorten the fan motor life. For instance, a condenser with nine fans would have each fan cycling control turn three fans on and off at the same time.

This D P between the evaporator and the LPC connection will result in an increase in the differential setting. Fine-tuning the differential setting should produce the desired results.

Refrigerant Pressure – Temperature Chart

Request Our Free Catalog. The final chosen differential has to be a compromise. Figure 1 shows the usual starting chqrt points to set up a LPC for various applications. A 35 to 50 psi differential is suggested, depending on usage. The refrigerant pressure increases, causing the LPC to cut-in, starting the compressor.

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 fhart of the compressor. As an example for a beer cooler: Figure 4 is typical fhart the piping for a pump-down system.


Refrigerant temperature is the design suction temperature when the compressor is on.

Figure 8 is a chart for condensers with multiple fans. Usually it is advantageous to keep the compressor on as long as possible for maximum efficiency.

Uses of Refrigeration Low Pressure Controls | Industrial Controls

Wiring is simplified and installed cost is reduced. For units located indoors, determine the lowest operating temperature of the unit. Figure 3 is a guide for setting the LPC for outdoor units.

This will be the cut-in setting. The settings in Figure 1 are only a beginning reference. An LP fan cycling control senses discharge head pressure and closes on rise of pressure. Since we pf the cut-in we want, this is easily determined. Since these systems are small and usually closely coupled, the Char P in the suction line should be somewhere around 2 to 4 psig. Two settings need to be made on the LPC: This type of control is most popular in small-refrigerated boxes such as beer coolers.


The LPC cut-in setting should be selected first. Very large condensers having four or more fans, usually have the fan cycling controls control two or more fans at a time. Figure 404z shows suggested pressure settings for a single fan condenser.

Allow 2 – 3 psi for suction line D P. As box temperature decreases, the evaporator temperature decreases, and a lower suction pressure results.

The TD of the evaporator coil.

P T Chart 404a

Variations chatt systems will probably require small corrections of the settings. The control opens on a fall in head pressure and shuts off the condenser fan, or fans. 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 cjart cause motor overheating or inadequate lubrication.

Indoor unit, RA refrigerant. The same is not true for a standard temperature control. To set the differential, and consequently the cut-out setting, four factors need to be determined: Set the differential at 11 psi. Short cycling, due to door openings, etc.

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