Air compressors are useful tools in many carpentry and mechanical jobs but compressors must be adjusted properly to ensure maximum performance. For example, pneumatic nail guns allow much faster installation of carpentry projects if the air compressor is adjusted to drive nails to the correct depth. If the pressure is too low, nails will not fully seat in the lumber. If the pressure is too high, nails will sink too deep and cause indentations in the lumber.
Remove the air compressor's pressure switch cover. The pressure switch cover is a black plastic cover on top of the air compressor. It is removed by turning the screw on top of the cover counterclockwise with a Phillips screwdriver. Set the cover aside.
Plug in the air compressor and turn the on/off switch to the on or automatic position. The air compressor will start immediately. Let the air compressor run until it shuts off. Observe the compressor's pressure gauge while it is running and take note of the pressure reading when it stops running. This is the cut-out pressure setting.
Bleed the air out of the air compressor. First, attach the hose by pulling back on the air fitting and sliding the fitting onto the air compressor nozzle, then releasing the hose nozzle. Attach a blowgun air tool to the opposite end of the air hose in the same manner.
Press the handle down on the blowgun to release air from the air compressor while watching the air pressure gauge. The air pressure gauge will show a decrease as air evacuates the tank. Take note of the pressure reading when the air compressor restarts. This is the cut-in pressure. Wait until the air compressor stops.
Use a small flat screwdriver to turn the compressor's main calibration screw to the right to increase the cut-in pressure. Turn the screw to the left to decrease the cut-in pressure. Test the pressures by bleeding air out of the air compressor and repeating these procedures until reaching the correct cut-in pressure.
Adjust the cut-out pressure of the air compressor by turning the differential pressure screw with a small flat screwdriver. Turn the screw clockwise to increase the differential or counterclockwise to decrease the differential pressure. Bleed air out of the air compressor as in the first adjustment and notice the pressure reading on the air pressure gauge. Continue bleeding and adjustments until reaching the correct cut-out pressure.
The main calibration screw is either above the differential adjustment screw, to the left of it or is the only metallic screw. Refer to the air compressor owner's manual to identify each adjustment screw correctly. Set compressor adjustment screws in the order specified. Reversing the order results in the main calibration pressure moving with each adjustment to the differential. This process will change both the cut-in and cut-out pressures at once and make them hard to calibrate. Differential pressure is the difference between the cut-in and cut-out pressure rates.
Refer to the owner's manual for the minimum differential pressure the manufacturer recommends. If the differential is lower than the suggested minimum, the air compressor will turn on and off too quickly and the motor will not cool properly between cycles.