Things You'll Need
Air compressor or air source
Low air pressure switches are useful and serve various purposes in the house. These switches can be found on devices such as shop air compressors, central ventilation fans and some water heater models. Sometimes you may have to test the switch if the device that has the switch is malfunctioning. Testing the switch for function will help you troubleshoot and isolate the source of the malfunction. You can utilize the low air presure switch troubleshooting process for high pressure switches as well.
Remove the electrical power to the device by unplugging it or shutting off the electrical breaker that supplies its power.
Take off the low pressure switch cover by removing the center screw with the appropriate screwdriver.
Isolate the two wires running from the low pressure switch to the terminal block and disconnect them. You will know these wires by their colors -- either brown or blue. Do not disconnect the black and white wires, as these are for power.
Use an air compressor to apply air to the low pressure switch.
Apply one lead of the ohmmeter to the end of one of the exposed wires and the second lead to the other wire while air pressure is being applied to the low pressure switch. You will get a zero ohm reading if the switch closes while air pressure is being applied, which means the low air pressure switch is in good condition. You will get an "OL" reading, for "Open," if the switch does not close. If this is the case, you need to adjust the set-point switch.
Turn the set-point screw counterclockwise as you are applying air pressure to the low pressure switch. If the switch still does not close, the switch is damaged and needs replacement.