Freon works as the refrigerant in air conditioning systems. Because the chemical is under pressure, the typical way of measuring the amount of Freon is based on the pressure within the closed refrigeration system. Some gauges measure both the pressure as well as the temperature. The pressure lets you know if it is the proper range for the device and is considered the "charge" of the unit.
Open the hood of your automobile and locate the air conditioning system. Your vehicle's manual tells you where in the engine compartment the AC unit lies.
Find the proper service fitting coming from the unit. If you are using a high-pressure gauge, attach the hose to the high-pressure outlet. If you are using a low-pressure gauge, fasten it to the low-pressure outlet.
Start your engine and turn the air conditioning to the maximum possible coolness and fan level.
Check the pressure level on the gauge. The low pressure ranges between 25 and 40 psi. A high-pressure gauge should range between 200 to 225 psi.
