How to Charge a Home AC Compressor With R-22


Most homes with an air conditioning system manufactured before January 1, 2010 use R-22 as the refrigerant. The AC compressor circulates the refrigerant through the system's pipes, metering devices and coils. AC systems with a low R-22 charge do not perform at peak efficiency. In a clean and sealed system, an R-22 charge of less than 58 psi forms ice on the evaporator coil -- the inside coil. If the AC system has clean, leak-free coils, a clean filter and both fans operating at the correct speed, then charging an AC with the correct amount of refrigerant maintains peak performance.

Things You'll Need

  • Adjustable wrench
  • R-22 manifold gauges
  • Thermometer
  • Pressure/temperature chart
  • Turn on the air-conditioning system. Turn the thermostat to its coolest setting.

  • Remove the caps covering the outside AC unit's R-22 refrigerant valves. These are found on the pipes entering the outside unit. Some valve covers twist off by hand, and some require an adjustable wrench.

  • Screw an R-22 manifold gauge's left-hand hose onto the valve on the large refrigerant pipe. Only charge an AC system with gauges designed for R-22, as stated on the left-hand gauge.

  • Screw an R-22 manifold gauge's right-hand hose onto the valve on the small refrigerant pipe.

  • Purge the air from the manifold's hoses. Open each manifold handle for one second. The air in the hoses will exit the manifold's middle hose.

  • Screw the R-22 manifold gauge's middle hose onto a jug of R-22 refrigerant.

  • Turn the R-22 jug upright, so its valve faces upward. Open the R-22 jug's valve. This keeps the liquid refrigerant away from the valve.

  • Let the system's refrigerant pressures equalize. The needle on the left-hand gauge will stop falling, and the needle on the right-hand gauge will stop rising when the system has equalized. This can take from three to five minutes.

  • Look at the psi reading on the left-hand gauge. If the gauge reads below 60 psi, then open the left-hand gauge's handle for 30 seconds. Allow the pressure to equalize. Repeat this until the psi reading reaches 60. Allow the system to run for five minutes.

  • Place a thermometer on the large refrigerant pipe 6 inches from the service valve. Take the thermometer's reading, called super-heat, once it has stopped dropping.

  • Find the refrigerant pressure that relates to the thermometer's reading. If the manifold's left-hand gauge has a temperature scale next to the psi scale, then use it. If not, then use a pressure/temperature chart -- called a P/T chart.

  • Compare the super-heat reading to the gauge's psi reading. If the super-heat reading is more than 20 degrees above the P/T chart's reading, then add R-22 until the super-heating reading reaches the optimal range -- between 8- and 18-degree super-heat, depending on the environmental conditions. Many technicians charge the system until it has a 12-degree super-heat; about 70 psi at 85 F. If the super-heat reading is below 7 degrees, then the system usually has an overcharge, a stuck metering device or a dirty coil.

  • Close the R-22 jug's valve. Then disconnect all of the hoses, and replace the service valve caps.

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  • Photo Credit Schäferhund image by Angelika Bentin from
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