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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It is a good starting point.

The LPC cut-in setting should be selected first. Set the cut-in at 18 psi. Usually it is advantageous to keep the compressor on as long as possible for maximum efficiency. This D P between the evaporator and the LPC connection will result in an increase in the differential setting. For instance, a condenser with nine fans would have each fan cycling control turn three fans on and off at the same time.

This will be the cut-in setting. Figure 4 is typical of the piping for a pump-down system. 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. Unless gauges are installed at the outlet of the evaporator and at the LPC connection to the system, not practicalthis Chatr P can be estimated. 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.

Two settings need to be made on the LPC: To control box temperature with a low-pressure control, the system must use a thermostatic expansion valve, non-bleed type. The differential chosen will determine the compressor on time. Even low temperature freezers using R or RA should not be set lower than 0 psi cut-out. The settings in Figure 1 are only a beginning reference. Figure 7 shows suggested pressure settings for a single fan condenser.


Fine-tuning the differential setting should produce the desired results. 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: There are some advantages p this type of system. Testing Wireless Solutions Testing wireless transmitters link.

Figure 5 and Figure 6 cjart two of the more common cahrt diagrams for pump-down systems. 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.

Refrigerant Pressure – Temperature Chart

Allow 2 – 3 psi ppt suction line D P. The TD of the evaporator coil 3. Since we know the cut-in we want, this is easily determined. The same is not true for a standard temperature control. A 35 to 50 psi differential is suggested, depending on usage.

Since these systems are small and usually closely coupled, the D P in the suction line should be somewhere around 2 to 4 psig. Unless you were the designer of the box, you may not know the design TD picked for the system. 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. Too small a differential will cause short cycling of the condenser fan and shorten the fan motor life.

As box temperature decreases, the evaporator temperature decreases, and a lower suction hcart results. The refrigerant pressure increases, causing the LPC to cut-in, starting the compressor.

Refrigerant temperature is chaart design suction temperature when the compressor is on. Wiring is simplified and installed cost is reduced. 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. 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 control opens on a fall in head pressure and shuts off the condenser fan, or fans.

In a pump down system, a thermostat controls a solenoid valve in the liquid line. Request Our Free Catalog. The final chosen differential has to be a compromise. Below that, flooded condenser valve systems should be used.

Product Code Quantity 1 2 3 4 5. 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.

Remember—too close a differential may maintain close temperature control, but cause short cycling, greatly shortening equipment life. The TD of the evaporator coil. This type of control is most popular in small-refrigerated boxes such as beer coolers. Variations in systems will probably require small corrections of the settings. Figure 8 is a chart for condensers with multiple fans.

December 13, – 1: Figure 1 shows the usual starting set points to set up a LPC for various applications. To set the chatr, and consequently the cut-out setting, four factors need to be determined: For units located indoors, determine the lowest operating temperature of the unit.

Refrigerant Pressure – Temperature Chart

Set the cut-in at 31 psi. Figure 3 is a guide for setting the LPC for outdoor units. TD is the temperature difference between the box temperature and the refrigerant temperature in the evaporator.