How to Read R22 Low Side Pressure

If you have an air conditioning system that contains R22 refrigerant, then it is important to know how to read the low side pressure. If you are unsure how to do this, take a piece of paper and line up the pressure reading with the corresponding temperature chart for that specific refrigerant.


The temperature of r22 low side pressure is important because it determines how well the refrigerant is transferred to the condensing coil. When the temperature of the refrigerant goes up, it increases the pressure, too.

If you’re in the HVAC field, you know what this means: a high temperature or high pressure on the r22 low side can mean an air conditioner that isn’t running correctly. Typically, the r22 low side pressure should be around 60 PSI to 85 PSI.

The temperature of r22 low side pressure depends on the type of refrigerant used and the operating conditions in the system. You can consult an r22 temperature chart to find out the best pressure for your application.


A typical residential air conditioning system has a suction line that connects the outdoor compressor motor to the indoor coil of the evaporator. A sealed vacuum test gauge is connected to the suction line in order to measure low side pressure during compressor operation.

Typically, the suction vacuum (negative) pressure for a compressor motor is determined by charging charts that are provided in service manuals. These charts are designed to target a specific suction vacuum (negative) pressure and output high-side compressor pressure for each model, compressor motor size and refrigerant type.

For example, the target suction vacuum (negative) pressure for an R22 evaporator running at 40F saturation temperature is 68.5 psig. Should the suction pressure drop below 57 psig, the evaporator coil will begin to freeze-up.


R22 refrigerant is a toxic chemical that depletes the ozone layer and is slowly being phased out of use. In the meantime, it is a good idea to upgrade your air conditioning system to use a newer, more environmentally-friendly refrigerant.

Superheat is a function of the temperature and pressure of the liquid refrigerant. It is an indication of how much heat load can be handled by the evaporator coils.

The best way to determine the proper level of superheat is to follow the manufacturer’s specifications for the equipment in question. This information is normally listed on a charging chart inside of the condenser or on the installation manual for the equipment.

Another method is to calculate the suction gas temperature at the expansion valve’s remote bulb location. This temperature is then subtracted from the saturation temperature of the suction gas (determined using a Pressure-Temperature chart) to get the superheat.


Subcooling is the process that occurs inside of your condenser coil just before refrigerant leaves and moves on to the evaporator coil. It’s a key element in air conditioning efficiency because it helps refrigerant absorb heat.

One way to check if your system is suffering from subcooling issues is to measure the temperature of the liquid line that runs from the evaporator to the expansion valve. Set a thermometer roughly six inches from the liquid line and take notes of the reading.

Then subtract the corresponding evaporator saturation temperature and you’ll have a good idea of how much refrigerant is leaking from your system.

The pressure of R22 is typically between 260 psig and 76 psig on a 65-degree day, but that can vary based on the model, compressor motor size and design. That’s why it’s important to check your “Charging Charts” in service manuals to determine target suction vacuum (negative) pressure and output pressure for each compressor motor.

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