Kitchen Designs

Understanding R-22 Operating Pressures

R-22 has been phased out as a refrigerant and many comfort air conditioning systems are now using the newer, higher-pressure replacement refrigerant R-410A. As a result, this requires technicians to gain additional knowledge and training on the differences between the two refrigerants.

It also means that gauge manifold sets, hoses, recovery cylinders and the recovery machine must be rated for working with R-410A. This is a major safety issue.

High Side

R22 is a refrigerant used in many older air conditioning and refrigeration systems. However, it has been phased out and replaced with R 404A or R407C.

If you have an r22 vehicle, check your AC high side operating pressures to make sure they’re within the normal range of what your system should be doing. If they’re not, it could be an issue with your condenser or the compressor itself.

Your high side pressure gauge should read between 125 and 175 psi when your system is working correctly. If it’s too low, you need to get a mechanic to check it out.

When it comes to the low side, your AC compressor pressure gauge should read between 25 and 35 psi when you turn the system on. If it’s too high, it could be a leak in the system that needs to be repaired.

Low Side

The low side operating pressures of r22 vehicles vary as a function of the refrigerant used, compressor model and size. They can also vary as a result of changes in the ambient temperature of the building and the outdoor air temperatures at which refrigerant is returned to the compressor.

Typical residential unit refrigerant pressures are based on “Charging Charts” that are provided in service manuals to determine target suction vacuum (negative) pressure and output pressure for a specific compressor motor.

This “rule of thumb” gives pressures a bit higher than shown in our R-22 pressure and temperature table above. Calculated pressure: R-22 High-Side pressure = (75 x 2) + 50 which is 200 psig.


Suction Line

The suction line operating pressures of r22 vehicles are typically less than 100 psi. However, this may not be the case in your system because of variations in refrigerant, refrigerant type, evaporator/condenser design, outdoor ambient temperature, and more.

Some manufacturers have published charts showing what the suction line pressure should be for a certain refrigerant, based on the system, lines and current temperature. These are very useful to technicians.

In general, when using R-22, the vapor line suction pressure should be 35-40 degF below the building’s return air temperature measured at the air handler/furnace. This is also called the “design temperature difference.”

Discharge Line

R22 (hydrochlorofluorocarbon 22) is a refrigerant that’s being phased out because of its ozone depletion and global warming potential. However, it can still be found in older HVAC devices such as air conditioners and refrigerators.

The discharge line operating pressures of R22 vary depending on the outdoor temperature and indoor humidity. A general rule is that a properly charged unit should have a discharge line temperature of 100@ above ambient.

However, this rule of thumb is only useful as an indication and doesn’t always reflect actual performance of the system. For example, if the discharge line is too hot, you may add refrigerant to lower it. On the other hand, if the discharge line is too cold, you may remove refrigerant to raise it. This can lead to system problems such as oil starvation or compressor damage. So, it’s important to get accurate readings of the liquid and suction line temperatures as well as the discharge line temperature.

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