Most homes with air conditioning systems built before January 1, 2010 use R-22 as the refrigerant. The air conditioner compressor circulates the refrigerant through the system’s piping, metering devices, and exchangers. Air conditioning systems with low R-22 charge do not perform at peak efficiency. In a clean, sealed system, an R-22 charge of less than 58 pounds per square inch (psi) forms ice in the evaporator exchanger (on the inside surface of the exchanger). If the air conditioning system has clean, leak-free exchangers, a clean filter, and both fans running at the proper speed, then charging the air conditioner with the correct amount of refrigerant maintains its maximum efficiency.
Turn on the air conditioning system. Turn the thermostat to its coldest setting.
Remove the caps that cover the outside R-22 refrigerant valves. These are located on the piping going into the outdoor unit. Some caps are turned by hand, others require an adjustable wrench.
Screw the left hose from the R-22 gauge manifold to the valve on the large refrigerant line. Only charge air conditioning systems with gauges designed for R-22.
Screw the right hose from the R-22 gauge manifold to the valve on the small refrigerant line.
Bleed air from the manifold hoses. Open each manifold handle for one second. The air in the hoses will go out the center manifold hose.
Screw the center manifold hose from the R-22 gauge onto a canister of refrigerant.
Place the canister in an upright position, so the valve is pointing up. Open the valve. This keeps the refrigerant away from the valve.
Allow the coolant pressures in the system to equalize. The needle on the left gauge will stop going down, and the needle on the right gauge will stop going up when the system has equalized pressures. This may take three to five minutes.
Look at the psi reading on the left gauge. If the gauge reads below 60 psi, open the left hand crank for 30 seconds. Allow the pressures to equalize. Repeat the procedure until the psi reading approaches 60. Run the system for five minutes.
Place a thermometer in the large refrigerant line 6 inches from the service valve. Note the thermometer reading, called superheat, once it has stopped dropping.
Find the coolant pressure that corresponds to the thermometer reading. If the left manifold gauge has a temperature scale next to the psi scale, use that. If not, use the pressure/temperature chart called the P/T chart.
Compare the superheat reading to the psi gauge reading. If the superheat reading is more than 20 degrees higher than the P/T chart reading, add R-22 until the superheat reading reaches the optimum range – between 8 and 18 degrees superheat, depending on ambient conditions. Many technicians charge the system until it is 12 degrees superheat; approximately 70 psi at 85 degrees Fahrenheit. If the superheat reading is less than 7 degrees, then the system may have an overload, a stuck gauge or a dirty exchanger.
Close the valve on the R-22 canister. Then disconnect all hoses, and replace the service valve caps.
Tips
Only U.S. Environmental Protection Agency-registered technicians may legally purchase R-22.
Warnings
The right hose connects to a high-pressure refrigerant line. High-pressure R-22 can cause frostbite damage when it touches the skin. The right gauge should never read more than 300 psi.