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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An LP fan cycling control senses discharge head pressure and closes on rise of pressure.

Refrigerant temperature is the design suction temperature when the compressor is on. The TD of the evaporator coil. For instance, a condenser with nine fans would have each fan cycling control turn three fans on and off at the same time.

Refrigerant Pressure – Temperature Chart

Indoor unit, RA refrigerant. Very large condensers having four or more fans, usually have the fan cycling controls control two or more fans at a time. Short cycling, due to door openings, etc.

The differential is the difference between the cut-in and the cut-out pressures. The pressure control for each fan should be set to cut-in about 10 psi apart. Allow 2 – 3 psi for suction line D Chadt. Figure 3 is a guide for setting the LPC for charrt units. Avoid cut-out settings that result in a vacuum. The compressor will now go on at 33 psi and go off at psi suction pressure. This D P between the evaporator and the LPC connection will result in an increase in the differential setting.

Even low temperature freezers using R or RA should not be set lower than 0 psi cut-out. As an example for 044a beer cooler: The control opens on a fall in head pressure and shuts off the condenser fan, or fans. Too wide a differential will cause large fluctuations in head pressure and cause TXV hunting.


Figure 4 is typical of the piping for a pump-down system. Set the cut-in at 18 psi. 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 chrt and condenser, reducing the refrigerant pressure to the cut-out setting of the LPC and stops the compressor. The TD of the evaporator coil 3. Set the cut-in cuart 31 psi.

By cycling the compressor in response to the suction low side pressure, box temperature can be controlled.

Uses of Refrigeration Low Pressure Controls | Industrial Controls

The refrigerant pressure increases, causing the LPC to cut-in, starting the compressor. As box temperature decreases, the evaporator temperature decreases, and a lower suction pressure results. 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 final chosen differential has to be a compromise. This will be the cut-in setting. To control box temperature with a low-pressure control, the system must use a thermostatic expansion valve, non-bleed type.

There are some advantages to this type of system. A wide differential will give longer running time, but may cause wide temperature swings. Two settings need to be made on the LPC: Set the differential at 11 psi.

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.

Uses of Refrigeration Low Pressure Controls

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


To set the differential, and consequently the cut-out setting, four factors need to be determined: The same is not true for a standard temperature control. The settings in Figure 1 are only a beginning reference. For condensing units outdoors, py the coldest unit 404q temperature or the coldest ambient temperature selects the cut-in setting, whichever is the lowest temperature.

December 13, – 1: 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. Testing Wireless Solutions Testing wireless transmitters link. Unless you were the designer of the box, you may not know the design TD picked for the system. If, during the off cycle, refrigerant leaks into the low side to raise the pressure to chartt 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.

Usually it is advantageous to keep the compressor on as 404q as possible for maximum efficiency.

It is a good starting point. Figure 7 shows suggested pressure settings for a single fan condenser. If the beer cooler, used as previous example, were to use a pump-down system, 4404a LPC cut-in setting would be determined as follows: Our example of a beer cooler could be set up as follows: