Teach Me: Fixing an air compressor pressure switch

I just picked up a 60 gallon air compressor for cheap. The reason: it won't turn on. It will run if you bypass the pressure switch with a jumper wire. The pressure switch looks like this:

From the googles the springs set the kick on and off pressures. I'm assuming that the contacts in the kick on switch are dirty. Any idea on how to get at them?

Thanks,

Hmmm.

My guess here is that as the pressure increases to a certain level it pushes up on the bottom plate and the contacts open to turn off the motor. In other words this is a normally closed switch that opens when a certain level of pressure is reached.

If this is the case I'd put money on the mechanism being bound up rather than the contacts being worn. Can you find the moving parts and "exercise" them with the power off? Maybe ten or so cycles would do it. Some electrical grade lubricant may be helpful too- I would assume that bottom plate is guided by something. A couple squirts between the plate and the guiding surface could do wonders!

If the contacts are simply dirty you can try cleaning them with some aerosol contact cleaner, but if they've arced and are sticking I'd replace the switch. It's one thing to have the switch fail in the off position but you really don't want it to fail in the on position.

Thanks guys, got it working. I was able to remove the grey switch part from the spring assembly. The contacts were black with carbon and the plastic was slightly melted near the contacts. I cleaned the contacts with a file and reassembled it. Works well now and the contacts don't get warm now.

It looks like you could also use a points file through the square ports on the side to clean the contacts without disassembling the switch.

Usually they fail from the contacts burning or breaking up (fatigue from hammering back and forth) from use. Saw it happen on my parent's well switch, we were smacking it for a few days to keep it working till the weekend, I was horrified when I swapped it out and tore down the old one. One wrong move would have had a 220 volt 30 amp dead short. A new ~$25 Square D is a cheap way to avoid an electrical fire.

a replacement switch is cheap..

Some of those switches have a valve built in and the compressor output runs through them in such a way that when the compressor motor initially starts the compressor vents instead of building pressure in the tank until the motor is up to speed. Much easier starts, longer component life. If you find yourself having to replace it you may want to look at different types.

Along the same vein, one of the single best mods you can do is to tap a wire into your switch and use it to open a solenoid valve on the drain through an orifice or cracked open valve. When the compressor runs the drain will blow down a bit and you won't have to worry about the bottom of the tank rusting out.

Cheap as in $9.99 cheap....but wait there's more... http://www.surpluscenter.com/Electrical/Switches/Air-Pressure-Switches/

This switch has the unloader valve option. A replacement for this model switch is $40-$60 from my googling. I will see how my repair works, and if it seems iffy I will replace it.

In reply to oldopelguy:

That's a good idea. I noticed the tank had some water sloshing around it it when I was transporting it.

Mine just started popping the breaker everytime it comes on. I was told It was the pressure switch but unless it's stuck I can't see it doing that.

chandlerGTi wrote: Mine just started popping the breaker everytime it comes on. I was told It was the pressure switch but unless it's stuck I can't see it doing that.

Sounds like a bad motor to ground or a bad capacitor?

I was thinking it was a cap but I haven't had time to mess with it.

I don't think a shorted start or run cap will throw a breaker instantly. I bet you'll find the contacts in the switch have broken off and shorted between the poles.

My air compressor sometimes will start really slowly and if I turn off the lights it can help. Sometimes popping the blow off valve helps too. I don't think it's got a start cap, but I think I should add one.

I think the wiring to the garage is substandard.

In reply to RossD:

That's likely a wiring problem and really bad for the motor.