R22 is a commonly used refrigerant for residential, commercial and industrial air conditioning. It is slowly phasing out.
Many digital manifold gauges are equipped with pressure temperature charts for each refrigerant. You can use this information to determine superheat automatically without having to do any calculations.
The High Side
The r22 pressure chart high and low side is an interesting concept that shows the relationship between temperature and pressure. It is not just a fancy looking chart that looks great on the wall, but it can help you get the most out of your air conditioner or heat pump.
To illustrate, here are the hottest and coldest temperatures that R22 refrigerant can handle. At 95 degrees, you’ll be lucky to get a 125 degree condensing temperature (ambient plus 30 degrees). A cooler indoor temperature of 80 degrees will give you a 40 degree evaporating temperature. This is the smallest amount of R22 that you can safely charge into your compressor. The RT chart shows that at 85 degrees, the best you can do is 155.7 psi. The big news here is that this number translates to the same watts of electricity you’d pay for in a hair dryer, but for air conditioning and heat pump purposes it means you have to run your compressor longer to get the same results.
The Low Side
The low side of an air conditioning system involves the suction line, which connects the refrigerant gas from the evaporator to the compressor motor. This line usually has a relatively small value, less than 100 psi, which can be tested with a sealed vacuum test gauge.
When the compressor is off, the entire system pressure equalizes so that the low-pressure number stays close to the outdoor or room temperature. Therefore, it is a good idea to use this R22 PT chart to check what pressure the refrigerant gas is at different temperatures.
For example, on a 65-degree day, the pressure of R22 is 111.3 psig. This is within the normal operating pressure for the refrigerant. Similarly, on an 85-degree day, the pressure of R22 settles at 143.7 psig.
The Evaporator Saturation Temperature
At a certain pressure, the refrigerant in an HVAC system will begin to change from liquid into vapor. This process is called saturation.
The refrigerant must be at a certain temperature and pressure to enter this phase change, which is why you’ll find a chart for each refrigerant on the PT (pressure-temperature) charts. It’s an important tool for HVAC professionals to have on hand and one that can be used to solve problems.
This chart will show the evaporator and condenser temperatures for each refrigerant as well as their pressures at each temperature. This helps you diagnose problems with the evaporator and condenser as well as troubleshoot how much refrigerant is in the system.
The evaporator and condenser coils add and remove heat to the refrigerant, which allows the molecules to enter the liquid or vapor state. When the molecule is in the vapor or liquid state, it’s at the saturation temperature.
The Suction Saturation Temperature
R-22’s suction saturation temperature is similar to water’s boiling point in that it depends on the pressure. When the pressure increases, the temperature of the refrigerant changes as well.
This change of state allows the refrigerant to be converted from liquid to vapor. This process is called evaporation and can occur in a refrigeration system at the same time as condensation.
Essentially, the saturation temperature is the temperature at which the vapor pressure of the refrigerant equals the system pressure. This can happen because of the refrigerant’s own properties or it can be influenced by a combination of those factors.
There are several ways to calculate the evaporator or suction saturation temperature of a refrigerant. You can use a traditional PT chart or you can use digital manifold gauges that have the corresponding pressure temperature charts saved in their programming.