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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Figure 5 and Figure 6 show two of the more common wiring diagrams for pump-down systems. Figure 4 is typical of the piping for a pump-down system. The TD of the evaporator coil. This type of control is most popular in small-refrigerated boxes such as beer coolers. 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.
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. 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. Allow 2 – 3 psi for suction line D P. By cycling the compressor in response to the suction p side pressure, box temperature can be controlled.
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. Figure 3 is a guide for setting the LPC for outdoor units.
The refrigerant pressure increases, causing the LPC to cut-in, starting the compressor. Set the cut-in at 18 psi.
As an example for a beer cooler: Usually it is advantageous to keep the compressor on as long as possible for maximum efficiency. Figure 8 is a chart for condensers with multiple fans.
For units located indoors, determine the lowest operating temperature of the unit. There are some advantages to this type of system. A 35 to 50 psi differential is suggested, depending on usage. Unless you were the designer of the box, you may not chary the design TD picked for the system.
Figure 7 shows suggested pressure settings for a single fan condenser. The differential chosen will determine the compressor on time. 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. Unless gauges are installed at the outlet of the evaporator and at the LPC connection to the system, not practicalthis D P 044a be estimated.
Even low temperature freezers using R or RA should not be set lower than 0 psi cut-out. Since we know the cut-in we want, this is easily determined. The same is not true for a standard temperature control.
For instance, a condenser with nine fans would have each fan cycling control turn three fans on and off at the same time. Two settings need to be made on the LPC: 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: The pressure control for 044a fan should be set to cut-in about 10 psi apart.
A differential setting of 5 psi to 10 psi will result in a reasonable cut-out setting of 8 to 13 psi. Remember—too close a differential may maintain close temperature control, but cause short cycling, greatly shortening equipment life.
It is xhart good starting point.