R22 Pressures

R22 pressures are used in a wide range of air conditioning and heating devices. However, r22 refrigerant is starting to be phased out.

There are several reasons why r22 is being phased out. One is the fact that it is an ozone depleting substance. Another is the fact that it is dangerous for the environment.

Suction Pressure

A suction pressure is the pressure that is inside an air conditioning system when a refrigerant gas, like R22, comes from the compressor motor, through the suction line, to the evaporator. This value is usually less than 100 psi and can be tested by connecting the suction line to a sealed vacuum test gauge on the same line.

This pressure reading can be used as a reference for the normal operating or charging pressure of an AC unit and refrigerant. Typically, charts are published in manufacturer manuals or in local building codes showing what the suction line pressure should be for a number of refrigerants and based on the system, lines and current temperature.

Using the same refrigerant and compressor model, if the outdoor air temperature is 85 degrees, the service chart shows that the incoming or suction line pressure should be 75 psi. This is the low side or normal operating pressure of the compressor motor.

Discharge Pressure

Discharge pressures are the pressures at which a refrigeration system’s refrigerant condenses with the cooling medium (air or water) flowing across its condenser. They vary based on the type of refrigerant in use and the temperature of the available cooling utility.

R22, which is slowly phasing out due to its ozone depletion potential and high global warming potential, has an average discharge temperature of 34.5degC. This is 17 to 30degC higher than the temperature of R 410A.

The normal discharge pressure in a refrigeration system can be determined by a combination of the type of refrigerant in use, the ambient air or water temperature of the available cooling utility and the amount of sub-cooling required at the evaporator.

The normal discharge pressures of dry screw compressors without liquid injection can range from 2.5 to 6 depending on the gas molecular weight and isentropic exponent. However, a case-by-case decision is required.

High-Side Output Pressure

The high-side output pressure is the refrigerant gas pressure used to run the compressor motor, which compresses and condenses refrigerant. This pressure is called “output” and usually ranges from 260 psi on the low side to 76 psi on the high side, depending on the model of compressor motor and the refrigerant gas being used.

R22 is a low-pressure refrigerant gas that flows through the suction line and then into the air handler where it is compressed and converted to a high-pressure refrigerant liquid. This is done to transfer heat from a hotter space into a cooler space.

Low-Side Output Pressure

R22 pressures at low temperatures are typically lower than those of other refrigerants. This is due to the refrigerant being a bit less dense than R134a and requires a larger condenser to work efficiently.

When using R22 for residential air conditioning or heat pump systems, it is crucial to know the static or equalized refrigerant pressure at different ambient temperatures. This knowledge allows you to adjust the suction and discharge line pressures to match the ambient temperature for optimum performance.

A common rule of thumb is to subtract 45 degrees from the incoming air temperature. This should result in the low-side output pressure being about 75 psig when the outdoor air temperature is 80 degF or higher.