How to Calculate the Amount of Refrigerant in a R134A System

by Tom Price

Recharging an air-conditioning system with the correct amount of R134a is important if the air-conditioning system is expected to work properly. For instance, if a 2001 Toyota Solara is supposed to take 2.2 pounds of R134a and the technician only puts in 1.5 pounds, the air conditioner will not cool the vehicle down properly. While it is not important to be able to calculate the exact amount of refrigerant in an R134a system, it is possible.

Step 1

Remove the cap from the low-pressure or low-side service valve by turning it counterclockwise with an adjustable wrench, and unscrewing it by hand. The low-side service valve is normally located around the firewall in the engine compartment.

Step 2

Remove the cap from the high-pressure, or high-side service valve in the same manner. The high-side service valve is normally located somewhere on the left side in the front of the engine compartment. On some vehicles, it may also be located in front of the condenser for easy access.

Step 3

Pull back the sleeve on the air-conditioner charging station's blue low-side quick connector and attach it to the low-side service valve. Release the sleeve. Connect the red high-side service hose to the high-side service valve in the same manner.

Step 4

Set an empty R134a tank on a scale and weigh it. Make note of the weight.

Step 5

Attach the air-conditioner charging stations yellow line to the empty R134a tank.

Step 6

Evacuate the air-conditioning system, following the air-conditioner recharging station manufacturer's instructions.

Disconnect the R134a tank from the recharging station. Set the tank back on the scale. Subtract the weight of the empty tank from the weight of the tank after evacuation. The result will be the amount of refrigerant in the R134a system.


  • Since there are several different types of air-conditioning recharging stations, refer to the charging station owner's manual for instructions on specific machines.
  • Normally the amount of R134a in any air-conditioning is inconsequential. If a leak develops, it all leaks out and the system must be evacuated and recharged.
  • When recharging an AC system, the correct amount of refrigerant is indicated by the PSI readout on the low side gauge on the air-conditioning recharging station.


  • Do not discharge R134a or any other refrigerant into the atmosphere. Federal laws and some state laws provide strict penalties for doing so.

Items you will need

  • Adjustable wrench
  • Air conditioning charger station
  • Empty Freon tank
  • Scale

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