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 compressor will now go on at 33 psi and go off at psi suction pressure. The pressure control for each fan should be set to cut-in about 10 psi apart.

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.

Fine-tuning the differential setting should produce the desired results. By cycling the compressor in response to the suction low side pressure, box temperature can be controlled. For condensing units outdoors, either the coldest unit operating temperature cahrt the coldest ambient temperature selects the cut-in setting, whichever is the lowest temperature.

Figure 5 and Chwrt 6 show two of the more common wiring diagrams for pump-down systems. Figure 7 shows suggested pressure settings for a single fan condenser. What all this means is that one picks cut-in and cut-out settings that should result in good temperature control, monitors pf system, and then fine-tunes each specific job to achieve the desired results.

This type of control is most chadt in small-refrigerated boxes such as beer coolers.


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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. Wiring is simplified and installed cost is reduced.

Figure 3 is a guide for setting the LPC for outdoor units. An LP fan cycling control senses discharge head pressure and closes on rise of pressure. If the cart cooler, used as previous example, p to use a pump-down system, the LPC cut-in setting would be determined as follows: Request Our Free Catalog. 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. A 35 to 50 psi differential is suggested, depending on usage.

Set the cut-in at 18 psi. This D P between the evaporator and the LPC connection will result in an increase in the differential setting. 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.

Set the cut-in at 31 psi.

The final chosen differential has to be a compromise. Allow 2 – 3 psi for suction line D P. Figure 8 is a chart for condensers with multiple fans.

Uses of Refrigeration Low Pressure Controls

Our example of a beer cooler could be set up as follows: Since we know the cut-in we want, this is easily determined. Figure 4 is typical of the piping for a pump-down system. To control box temperature with a low-pressure control, the system must use a thermostatic expansion valve, non-bleed type.


Figure 1 shows the usual starting set points to set up a LPC for various applications. Indoor unit, RA refrigerant. Short cycling, due to door openings, etc. Even low temperature freezers using R or RA should not be set lower than 0 psi cut-out.

Variations in systems will probably require small corrections of the settings.

TD is cyart temperature difference between the box temperature and the refrigerant temperature in the evaporator. Testing Wireless Solutions Testing wireless transmitters link.

The differential chosen will determine the compressor on time. Usually it is advantageous to keep the compressor on as long as possible for maximum efficiency. This will be the cut-in setting. Below that, flooded condenser valve systems should be used. Remember—too close a differential may maintain close temperature control, but cause short cycling, greatly shortening equipment life.

As an example for a beer cooler: Two py need to be made on the LPC: The control opens on a fall in head pressure and shuts off the condenser fan, or fans. Since these systems are small and usually closely coupled, the D P in the suction line should be somewhere around 2 to 4 psig.

Avoid cut-out settings that result in a vacuum. These brief occasional cycles are not objectionable, but if they occur too often, are an indication of a leaky solenoid valve or leaky charr valves. There are some advantages to this type of system. December 13, – 1: It is a good starting point.