What has happened to it when your air compressor pressure switch is leaking air?
Essentially, there are two reasons why this can occur.
But first, lets talk about what the pressure switch does for the air compressor.
A pressure switch reacts to pressure. In the case of your air compressor, the pressure switch is typically plumbed so that the air from the compressor air tank can flow to the switch. It is the air in the compressor tank that the pressure switch is sensing.
Compressed air pressure pushes equally in all directions at the same time. So, if the tank gauge reads 120 PSI, then there is 120 lbs of force pushing on each square in of tank area, and through the line up to the pressure switch, 120 lbs. of force is pushing on each square inch of the diaphragm inside the pressure switch.
It is the tank pressure pushing on the diaphragm inside the pressure switch that causes the pressure switch to trip.
Why a compressor pressure switch is leaking air – reason one
Reason one why your compressor pressure switch is leaking air is that, over time, the diaphragm inside the switch has cracked or worn a hole, and air is blowing from inside the tank, through the hole in the diaphragm, and existing the switch housing through any convenient opening.
In the photo above, the electric wire ports would be logical places for air to exit the cover should the pressure switch diaphragm have become holed. If the wire strain-relief fittings fill the apertures in the switch, then it may be necessary to pull the cover off the switch to investigate for leaks. If you do this, ensure that the compressor has been unplugged from any power source.
In this photo, note also that the unloader valve for this pressure switch is located on the outside of the switch. If air is exiting the pressure switch cover, then it is almost certain that the diaphragm has failed. That may not necessarily be the case if the
If, when the air compressor has reached cutout pressure and stopped, you notice that air is blowing out any openings in the pressure switch cover, or if you remove the cover and feel air escaping, and particularly if the unloader valve is plumbed outside of the switch, then you either disassemble the switch and replace the diaphragm, or you replace the switch with one of the same pressure and voltage rating as the old model.
Getting parts for pressure switches may be difficult. Disassembling them and reassembling them is, too, quite complex, particularly when you may only do it once or twice in a lifetime.
If it were us, we’d simply purchase a new switch and replace the old. In this manner the removal and re-installation is straightforward, you get a new diaphragm in the switch, and you also get new points, which are another wear item in a typical compressor pressure switch.
Why a compressor pressure switch is leaking air – reason two
If you notice that the pressure switch on your compressor is leaking air, locate the unloader valve, and try to determine if the air is leaking from the unloader valve or from the switch itself.
If air is leaking from the unloader valve when the air compressor is stopped, that points to a problem with the compressor tank check valve not seating properly, or its failure.
If the air is leaking from the unloader valve, then see the page under Fixing Compressor Problems about air continuously leaking from the unloader valve for more information.