Can you provide guidance for wiring pressure switch?

by michael ramphal
(florida)

It’s for a husky m#h27508uwk year manf 2004?

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Hey Michael. I could not find an image of your air compressor, but an on line compressor parts supplier showed a schematic kind of identifying the switch.

Many pressure switches have the schematic for that switch stenciled under the lid. I take it yours doesn’t?

If the image of the switch I saw is correct, you will have three wires coming to it from the power cord, and there will be 2 or three wires coming from the compressor motor.

Usually one of the wires will be green, and that’s the ground wire. Somewhere near the terminals on the switch there will be an image something like this… and that’s where the ground wires from the power cord and if one on the motor lines, get connected.

Ground symbol identifies the grounding terminal on an electrical device.

Ground symbol identifies the grounding terminal on an electrical device.

The pressure switch is just that… a switch. Instead of you flipping a toggle to allow power to flow through the switch, like you do to a light bulb, the pressure in the tank acts on a diaphragm inside the switch, which pushes against a spring. At a certain temperature, the pressure will push against the spring hard enough to cause it to flip to the other direction. This typically turns off the power.

When the tank pressure drops the spring flips the switch inside the pressure switch (usually called points) and the power stops flowing to the motor and the compressor stops, just like someone had tripped the light switch to off to turn off the light.

So, power (the power from the wall plug cord) has to be on one side of the terminals on the pressure switch, and the load (the other two wires from the motor have to be on the other side of the terminals inside the pressure switch, so that when the pressure switch trips to off, power from the cord cannot flow across the switch to the wires on the motor side.

Examine the terminals on both sides of the internals of the switch.

One set will likely say “line” or “power”. Those are the cord side, and the black wire and the white wire from the power cord side gets wired to  each of those.

On the other side of the switch the terminals may be marked “load” or “motor”, something to indicate that those are for the compressor motor. One black and one white from the motor goes to each of these.

Hope this helps.

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Pressure switch wiring instructions
by: SGT KILLDIE

First of all I’m quite sure there are SOME kind of schematics on a sticker or molded into the plastic, but if not, do this….

Pull the cover off of the switch (if i have to tell you to unplug it first, then you’ve got more problems than i can solve)

The switch will most likely have 2 bars which move up and down when you hit the on/off switch.

Locate these and wire the white from the wall to the moving contact and the white from the motor to the fixed contact.

Do the same on the other side with the green wires. and obviously the black will be your ground which is most likely going to be mounted to a nearby screw, which should have a small symbol on or near it that looks like one of those 70’s era tv roof antennas. I’m not an expert, but this is pretty basic stuff…Hope this helps.

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Nope!

Black is Ground?
by: Anonymous

Wouldn’t black and white be the power wires and green the grounding wire?


Wiring hook up questions.

How do the electrical wires hook up on the pressure switch?

On the electrical hookups on the switch it reads line on one side and motor on the other.

The name brand of the switch is Furnas electric co.

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Hello, and thank you very much for writing in.

If you take a look at some of the questions and answers on this page, you’ll find photos and help.

Pressure switch terminal wiring

Pressure switch terminal wiring

I’ve uploaded a photo of typical compressor pressure switch wiring.

The line wires are the supply, the motor terminals are the wires for the motor.

If you aren’t comfortable with what these mean, I don’t think you should be attempting your own re-wiring.

That’s why I always recommend that folks that aren’t comfortable with wiring theory take a digital photo of their wiring before they start to disconnect components, to help in the re-wiring process.