R134a Refrigerant Charge is widely used in the heat pump and refrigerator circuit, has a some industry related and commercial applications. It is a compound that go across a phase transition from a liquid form to a gas form and then again returns to a liquid form.
Some of the zeotropic blends have very less glide (from I° F to 2.5° F). For these blends, the vapor and liquid pressures are only separated by 1 or 2 psi. Because the difference is quite less between the two values some of manufacturers' PT charts only display one column for these blends. Blends with higher glide (greater than 5° F) will generally have both columns presented.
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Two-column PT Saturation chart:
When checking a superheat or subcool temperature the procedure is the same as for a single-component refrigerant. Superheat is tested by measuring the temperature of the vapor line, measuring the pressure, then subtracting the saturated temperature from the measured temperature. In the case of a blend, you Simply read the saturated temperature next to the pressure in the vapor (dew point) column of the chart.
When checking the subcool condition the technician will measure the temperature of the liquid line, the pressure at that point and subtract the measured temperature from the saturated temperature at the end of the condenser. With the blend you read the saturated temperature next to the pressure in the liquid (bubble point) column of the chart.
For a single-component or azeotropic refrigerant, the operating pressure for the low side of a system can be found by cross referencing the desired coil temperature on the PT chart. For high-glide blends, however, the desired coil temperature is the average (or midpoint) temperature of the coil.
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INTERPRETING PRESSURE READINGS |
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Low-Pressure |
High-Pressure |
Action |
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IN RANGE |
IN RANGE |
A/C is working properly. |
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LOW |
LOW |
Add Refrigerant. |
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LOW |
HIGH |
Need service, possible blockage of the |
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HIGH |
LOW |
Needs service, possibly faulty compressor. |
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HIGH |
HIGH |
System is overcharged. Slowly remove |
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It is illegal to vent 134a refrigerant into the atmoshpere. |
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The problem with two-column PT charts is that the conditions at the endpoints of the temperature glide are presented, not the midpoint. In this case, you should add half of the temperature glide to the desired midpoint temperature, then read the saturated vapor column to estimate the operating pressure