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

P T Chart 404a

Usually it is advantageous to keep the compressor on as long as possible for maximum efficiency. Unless gauges are installed at the outlet of the evaporator and at the LPC connection ppt the system, not practicalthis D P can be estimated. A differential setting of 5 psi to 10 psi will result in a reasonable cut-out setting of 8 to 13 psi.

This D P between the evaporator and the LPC connection will result in an increase in the differential setting.

This will be the cut-in setting. Too small a differential will cause short cycling of the condenser fan and shorten the fan motor life. Figure 3 is a guide for setting the LPC for outdoor units.

The control opens on a fall in head pressure and shuts off the condenser fan, or fans. Allow 2 – 3 psi for suction line D P.

Remember—too close a differential may maintain close temperature control, but cause short cycling, greatly shortening equipment life.

The Cart of the evaporator coil 3. Testing Wireless Solutions Testing wireless transmitters link. Indoor unit, RA refrigerant. Figure 8 is a chart for condensers with multiple fans. It is a good starting point.

Refrigerant Pressure – Temperature Chart

Below that, flooded condenser valve systems should be used. Since these systems are small and usually closely coupled, the D P in the suction line should be somewhere around 2 to 4 psig. 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. For instance, a condenser with nine fans would have each fan cycling control turn three fans on and off at the same time.


In a pump down system, a thermostat controls a solenoid valve in the liquid line. Figure 5 and Figure 6 show two of the more common wiring diagrams for pump-down systems.

The same is not true for a standard temperature control. TD is the temperature difference between the box temperature and the refrigerant temperature in the evaporator. The differential chosen will determine the compressor on time.

Our example of a beer cooler could be set up as follows: 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. Short cycling, due to door openings, etc. Since we know the cut-in we want, this is easily determined. Set the cut-in at 31 psi.

Wiring is simplified and installed cost is reduced. This type of control is most popular in small-refrigerated boxes such as beer coolers. As an example for a beer cooler: To control box temperature with a low-pressure control, the system must use a thermostatic expansion valve, non-bleed type. 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. 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.


Product Code Quantity 1 2 3 4 5. Very large condensers having four or more fans, usually have the fan cycling controls control two or more fans at a time. December 13, – 1: 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.

As box temperature decreases, the evaporator temperature decreases, and a lower suction pressure results. 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. Set the cut-in at 18 psi. Figure 1 shows the usual starting set points to set up a LPC for various applications.

Even low temperature freezers using R or RA should not be set lower than 0 psi cut-out. Unless you were the designer of the box, you may not know the design TD picked for the system. Two settings need to be made on the LPC: Figure 7 shows suggested pressure settings for a single fan condenser.

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. The pressure control for each fan should be set to cut-in about 10 psi apart. The LPC cut-in setting should be selected first. There are some advantages to this type of system. Too wide a differential will cause large fluctuations in head pressure and cause TXV hunting.

Last modified: January 6, 2020