This chart shows the four scales of measurement of pressure, we examined two for absolute pressure and excess pressure. Two pressure sensor scales are combined into one, because that's what they usually appear on the composite service rut.
Refrigerant pressure and temperature saturation are so closely related, that we need to know only one thing to know the other. Saturation temperature is really boiling point for the refrigerant. Any liquid boiling point is determined by the nature of the liquid and pressure on him. For example, the water is boiling temperature at sea level 212F at atmospheric pressure (PSIG 0 or 14.7 psi). If we enclose it in a pressure cooker and water pressure rises to 15 psi or 29.7 PSIA, its boiling temperature rises up to 250F.
For all liquids, the higher the pressure, the higher the boiling point, and less pressure causes a lower boiling point.
Refrigerant R-22 boils at -41 F at normal atmospheric pressure (PSIG 0). Unlike water, no fire is needed to make it boil because the surrounding 75F air provides enough heat to cause the refrigerant vigorously boil.
To obtain R-22 to a boil ("evaporate" in refrigeration terminology) at a temperature that has practical value for air cooling in comfort air conditioning system, it must be placed under pressure. Normal saturation temperature in the evaporator about 40F, which takes place in about 68.5 pounds per square inch. The pressure in the system determine the saturation temperature of the refrigerant.
Saturation temperatures, which correspond to various types of pressure, which can be quickly found for the refrigerant. For example, if you measure the pressure 68,5 PSIG evaporator coil, you can find a match saturation temperature in the left column Pressure-Temperature (P-T) card. For systems using R-22, 40F. Pressure for other refrigerants are also shown on the map. Since P-T-cards are intended for the use of the service people, pressure shown on them a pressure sensor.
In addition to the pressure of scale, some of the sensor sets the saturation temperature for the most common refrigerants printed on them. For sensor set, as shown here pressure reading (PSIG) corresponds to the saturation temperature -41 F on R-22 -28F the R-500. All you need to know what is the refrigerant into the system contains.
Although cooling, pressure can be used to determine the saturation temperature, these facts do not warrant that the refrigerant in the saturated. Temperature-enthalpy schemes used earlier in this module, we have seen that in any single refrigerant pressure can exist as a supercooled liquids, saturated liquid, saturated liquid-vapor mixture, vapour, or superheated gas. If liquid and gas States refrigerant are both present in one place, refrigerant on the saturation temperature.
If liquid is present, may be on the saturation temperature (saturated liquid), or it may be below the saturation temperature (supercooled liquid). The temperature will be needed in addition to the pressure reading to determine its condition.
The same applies to gas. For example, if the pressure on R-22 system reads 68.5 PSIG at the outlet of the evaporator coil, and the gas temperature measured by the refrigerant pipe evaporator-55F, then the temperature above the saturation temperature and superheated gas. This can be seen on the temperature-enthalpy diagram shown here.
This chart shows three refrigerant storage of cylinders; each of them has its liquid and gas States refrigerant. Notice how the pressure is the same for everyone. Pressure corresponds to the temperature of the refrigerant, which is the same as the air temperature in the place where they are stored. Liquids, saturated liquid and gas-saturated gas because the fluid and gas are present. Pressure is not changed because the amount of liquid and gas in each. We can say that both liquid and gas are shaking cylinder.
If the temperature in the room where the data is stored tanks came up to 100F and stayed there for a few hours, the saturation temperature of the refrigerant will also go up to 100F, as the heat from the room, crossing the steel wall of the cylinder in the refrigerant.
Pressure in each cylinder would rise to 195.9 pounds per square inch, that is the selection pressure, the saturation temperature of 100F on R-22. A practical way to apply their knowledge saturation temperature and pressure, it should be recognized that the temperature at which you store refrigerant cylinders will influence the pressure available from the cylinder for purposes of collection system. Cylinder R-22 stored outdoors in a very cold day will be very little pressure available for charging systems...