How To Wire And Adjust A Square D Pressure Switch
Square D pressure switches are commonly found on commercial air compressors. A faulty pressure switch will shut the air compressor down and you won't be able to use it again until you get a new one. Many people who use commercial air compressors may not know exactly how to wire and set the cut-in and cut-out pressure ranges on the switch. If you have a broken pressure on your air compressor and you're not sure how to wire the new one or set the pressure ranges, here is how you can wire and adjust the new pressure switch so you can start using your air compressor again.
Wiring the New Switch
After you've screwed the new switch onto the air compressor, you'll have to rewire it. Take the cover off of the switch to expose the four terminal connections for the wires. On some pressure switches, there are marking on the terminals so you know where to place the wires coming from the power cord and the wires going to the motor. If your switch doesn't have these markings, you should place the wires from the power cord on the outside terminals and put the wires going to the motor on the two inside terminals.
The power cord will have a black wire (which is the hot wire bringing the actual power to the switch) and a white wire. The white wire is neutral. You can place either wire on the outside terminals.
Adjusting the New Switch
Some new switches are pre-adjusted at the factory and others are not. If you have a switch that wasn't adjusted, or for some reason or another, got out of adjustment, here is what you should do.
There are two screws that you use to adjust the pressure on the switch. One screw is used to set the main cut-in pressure for the switch and the other screw is to set the cut-off for the maximum pressure the compressor should generate. The main cut-in pressure screw is the large one in the middle of the top of the switch. The cut-off screw is the small one next to the large one. You turn both screws clockwise to increase pressure and counterclockwise to decrease the pressure.
You should do the adjustments after you have installed the switch, restored the electricity, and hooked up the gauges so you can see the pressure readings you are getting. Refer to the owner's manual or consult professionals, like those from Compressor-Pump & Service, Inc., to find out what the pressure range should be set for the air compressor to make sure you set the cut-in and cut-out pressure screws properly.
