The A/C system of most automobiles uses freon coolant to lower the temperature of the car's interior. This coolant requires an amount of lubricant for the compressor and other equipment bushings to function properly. The oil is replaced in the same manner as the freon, through the low-pressure nipple with a valve kit. The average backyard mechanic can replace lost compressor oil in about 30 minutes.
Turn the valve to clockwise to close it, or make sure the trigger is released. Attach the can of lubricant to the valve's screw-on adapter. The adapter has a needle embedded into it that will puncture the can and pressurize the valve. Turn the can clockwise until it is tight, but do not over-tighten.
Attach the nozzle of the valve to the low pressure side of the A/C system by pushing the nozzle tip against the A/C line's nipple while sliding the nozzle tip's outer ring backwards. Release the ring and the tip will grab the nipple.
Crank the vehicle and turn on the A/C system to its maximum setting. Pull the trigger on the freon can valve, or turn the valve counterclockwise. The can will begin to hiss as the lubricant is sucked into the system by the vacuum of the line. If the valve has a gauge, the pressure will be shown with a needle on a color graph.
Disconnect the nozzle from the low-pressure nipple once the can is emptied, which should take about 2 minutes, then unscrew the can of lubricant. Attach another can, or a can of freon, and repeat the procedure until the system does not take in any more.
