When demand for air is high the pressure switch doesnt kick on properly.
by Kevin Karwat
(Reese, Michigan USA)
I replaced the pressure switch and after a couple of hours of use the switch did not engage and allowed pressure to run down thus shutting my machines down.
Bill replies...
Hey Kevin, nice to hear from Reese, Michigan.
A pressure switch is a (although complex to make I would think) a pretty simple device.
It's got a set of points inside that, when closed, allow electricity to flow to the motor.
When the pressure in the tank drops to the cut-in pressure, the spring overcomes the resistance from the air, and closes the points, and your electric motor starts. That's pretty much how they work.
If the pressure drops past the cut-in point and the points close, then electricity flows, and if the motor doesn't start at that point, then it's probably a capacitor or motor problem.
After you changed the pressure switch, were the cut-out and cut-in pressure levels correct? Did the compressor always start when the pressure dropped to the cut-in pressure level?
You mentioned that it ran for a couple of hours of use then failed. During that two hours, was the operation flawless?
Can you get your compressor running at all?
If so, then before you start it, very carefully (when the circuit is live the points will be exposed. You can kill yourself if you aren't careful) pull the cover from the pressure switch, turn on the compressor, and watch what happens when the pressure in the tank reaches cut-out pressure. Do you see the points shift to cut off the electricity flow?
Now, open a line and bleed down the tank well past the cut-in pressure. If you don't see movement in the points then it's likely the pressure switch...again.
If the points move, then you have to look at the capacitor or motor for your problem.
Cheers,
Bill
