Air compressors are useful tools in many carpentry and mechanical jobs, but they must be adjusted correctly to ensure maximum performance. For example, pneumatic nail guns make installation of woodworking projects faster if the air compressor is adjusted to insert nails at the correct depth. If the pressure is too low, the nails will not seat into the wood. If the pressure is too high, the nails will sink so deep that they will cause cracks in the wood.
Remove the pressure switch cover from the compressor. This is a black plastic cover on the top of the compressor. It is removed by turning the screw at the top of the cover counterclockwise with a Phillips screwdriver. Set the cover aside.
Plug in the compressor and set the switch to on or auto. The compressor will start immediately. Let it run until it shuts off. Watch the pressure gauge on the compressor while it is running and note the pressure reading when it stops running. This is the cut-out pressure.
Bleed the air out of the compressor. First, insert the hose by pulling the latch on the connector and sliding it onto the compressor nozzle, then release the connector from the hose. Insert an air gun into the opposite end of the hose in the same manner.
Press the gun handle to release some air while watching the pressure gauge. The gauge will show a decrease as air comes out of the tank. Note the pressure reading when the compressor restarts. This is the start pressure. Wait for the compressor to stop.
Use a small flat screwdriver to turn the main calibration screw to the right to increase the start pressure. Turn the screw to the left to decrease the start pressure. Test the new pressures by letting air out of the tank and repeating the procedure until the correct start pressure is achieved.
Adjust the compressor cut-in pressure by turning the differential pressure screw with the small flat screwdriver. Turn clockwise to increase the differential pressure or counterclockwise to decrease it. Bleed air from the compressor as you did for the first adjustment and observe the pressure reading on the gauge. Continue purging and making adjustments until you achieve the correct cut-in pressure.
Tips
The main calibration screw is located above the differential adjustment screw on the left or is the only metal screw. Consult the compressor owner’s manual to identify the correct adjustment screws.
Perform compressor adjustments in the order specified. Reversing the order results in the main pressure setting moving with each differential adjustment. This procedure will change both the start pressure and cut-in pressure at the same time complicating the calibration.
Warnings
Consult the manual for the manufacturer’s recommended minimum differential pressure. If the differential is less than the suggested minimum, the air compressor will cycle on and off too quickly and the engine will not cool properly between cycles.