Buying A Compressor
       Pressure Switch

While at first glance buying a compressor pressure switch is intimidating, breaking what you need to know into bite-sized chunks will make it easy for you to buy the right replacement compressor pressure switch for your make and model of air compressor.

Buying a compressor pressure switch is often a problem if the compressor is old and no OEM parts are available. Even if the air compressor is relatively new so many compressors available in today have no spare parts available at all.

Yet, since the compressor pressure switch simply turns the electric power supply to the compressor motor ON and OFF based on the pressure in the compressor tank, pressure switches for compressors with electric motors pretty much all work in a similar fashion. You just have to get the one that fits your air compressor. Here's how!

Buying a compressor pressure switch -
Just one type of compressor pressure switch.

The first step is to look at the existing pressure switch to see if there is a name or model number anywhere on it. The top of the pressure switch cover may have a name. A name and model number may also be on a label inside the cover. Please make sure that the power to the compressor is disconnected before removing the pressure switch cover. Did you find a name or model number? If so, Google that, and see if what pops up looks like your switch.

No luck with that? No worries. Here's how to carry on buying a compressor pressure switch.

If you simply Google "compressor pressure switch, you will find many different shapes, sizes and functions.

The things you will want to look for
              in the new, replacement pressure switch are:

The voltage of your air compressor.

When buying a replacement compressor pressure switch make sure the pressure switch you select has that same voltage as your compressor.

In North America if your compressor is plugged into a standard wall socket, then the voltage is 120 VAC. Some really small air compressors may have a transformer to convert 120 to 12 or 24 DC, but for other than tire inflators, that's not that common.

Usually a compressor with higher voltage than 120 VAC will have special wiring possibly including a control panel of some sort.

The switch voltage may not be a big issue anyway as many of the modern compressor pressure switches are rated for both 120 and 240 volt power supplies. Just check to be sure what the voltage your compressor is, and make sure that the switch you buy is rated for the same voltage or a range of voltages that includes that of your existing compressor.

What is the pressure range?

The pressure switch turns power to the compressor motor on and off. It does this by having pressure settings at which the switch opens to stop power flow, and closes to allow power flow to the compressor motor.

The pressure point at which the pressure switch allows power to flow to the motor is the cut in pressure setting. The pressure point at which the pressure switch stops power flow to the compressor motor is the cut out pressure setting.

Your old switch may have had a cut in of 90 PSI and a cut out of 120 PSI, for example. If you cannot remember the settings, look under the cover of the old switch, or in some cases, on the cover, for the cut in / cut out info. Or, check the compressor manual.

You need this information to obtain a new pressure switch that has either the same pressure settings as the old, or one that has adjustable pressure settings, so that you can set the new switch to the old settings. Do NOT vary the settings on the new switch by more than 5 PSI if you are setting them. The compressor is designed to be run within certain pressure ranges, and allowing pressures outside of those ranges can be hard on the compressor or result in a dangerous component failure.

The compressor pressure switch mounting?

The pressure switch must be able to "see" the pressure in the compressor tank. Therefore it will be mounted so that an air line connected to the tank will enter the pressure switch.

External compressor pressure switches typically have a threaded port in the bottom into which an air line is threaded. Some pressure switches have multiple ports. Some are bolted to a manifold, or threaded onto a pipe in a manifold.

Buying a compressor pressure switch -
This pressure switch is mounted on a manifold. The air path from the tank to the pressure switch is via a male thread under the manifold that is screwed into the compressor tank. The pressure switch is threaded onto a pipe protruding vertically from this manifold. Other manifolds may vary in shape and size..

Mounting of the pressure switch on the compressor can be accomplished in many ways. Carefully examine how the pressure switch is mounted on your compressor as you will need to select a replacement that mounts the same way.

Buying a compressor pressure switch -
This pressure switch has a base with multiple outlets. All of the outlets connect to the pressure switch, so which of these ports is plumbed to the compressor tank is immaterial. If this switch fits your compressor by using one of the holes in the base, if the pressure range is correct or adjustable, and the voltage is correct (this one is 120 VAC and 240 VAC) then this switch might work on your compressor. Unused ports in the base are plugged.

What are these things hanging on the side
              of my compressor pressure switch?

Have a look at the pressure switch in the photo below. It shows an ON/OFF lever on the left of the photo. Does your existing pressure switch have one of these?

Buying a compressor pressure switch -
In this view we see the bottom of this Lefoo pressure switch. On the left we see a lever. This is the ON/OFF switch for this pressure switch. Take a moment too to look at the various ports into which things like PRV's, regulators etc. can be plumbed.

I pull the plug on my air compressor after every use. Since the ON/OFF lever or switch essentially does the same thing - cutting the power supply to the pressure switch - I really don't see the need to have an ON/OFF switch on my compressor pressure switch too. If I were replacing my compressor pressure switch, I'd simply skip the ON/OFF lever. But... to make it easier for you, if your present switch has an ON/OFF lever (or similar) and you are not comfortable with changing the setup on your compressor, best to get one that's exactly the same.

Now, when you Google compressor pressure switches, you can skip all of the ones you see that do NOT have an ON/OFF lever or switch like yours.

Now let's talk a moment about the other thing that is commonly hanging on the side of, or found inside of, the typical external pressure switch. That is an unloader valve. If you aren't sure about what they do, see the information page on this site for complete details about what they are and what unloader valves do.

Buying a compressor pressure switch -
This pressure switch has an external unloader valve.

If your present pressure switch has an unloader valve located the side of the switch like, or similar to, the one shown in the photo above, you must acquire a replacement pressure switch that has the same type of unloader valve on the same side of the pressure switch as yours.

Otherwise you will be unable to install the replacement, or... and this is the voice of experience talking... you will spend an inordinate amount of time, bust a few knuckles, and turn the air blue as you try to fit the square peg into the round hole!

Internal Unloader Valve

Just to make things a bit more complex, a pressure switch may have an internal unloader valve. How do you tell if yours is one of these?

Buying a compressor pressure switch -
This pressure switch has an internal unloader valve.

If you have not removed your existing pressure switch from your compressor as yet, look under it, and see if there is an air line plugged into the bottom of the pressure switch. The air line may use a fitting like the brass colored fitting one in the photo above, or, it may be what is known as a "quick connect" fitting. That's a fitting with a hole in it into which you push the air tube.

Typically, the air line connected to the bottom of the pressure switch unloader runs from a fitting in the tank. This is also where the line from the pump head is connected to the tank.

Once again, you need not get an exact replacement for your compressor pressure switch if you are comfortable modifying components. Otherwise, when selecting your replacement switch, make sure you get one with an unloader port in the bottom of your new switch if there is one in the old.

How do the wires connect through the pressure switch cover?

This next photo has a red box drawn around the point where, on this switch, the cables enter the switch..

Buying a compressor pressure switch -
The cable access connectors on this switch are outlined in red.

There are two "cables" that connect to a typical switch. One is the power supply cord or cable which has the plug on it, and the other is the cable or wires that go from the pressure switch to the motor circuit on the compressor.

When you look at your existing pressure switch, how is the power supply cord getting through the pressure switch cover? How are the wires going to the motor from the pressure switch exiting the pressure switch cover. Are the wires on your existing pressure switch passing through "strain relief" connectors like the one shown in the photo above?

While strain relief connections are not specifically required, they are useful if circumstances result in the power cord ever being pulled aggressively away from the compressor, like, you forget to unplug it and roll the compressor away to a new location. Just make sure that you know how the power supply to the pressure switch and from the pressure switch to the motor can get through the pressure switch cover on the new model.

A brief recap

In order to buy a new pressure switch, you need to know:
  • check to see if there is an existing make and model number on the switch to make finding a replacement easy
  • what the compressor voltage is
  • what the pressure range of the old switch was
  • how the existing switch is mounted onto the compressor
  • whether the old switch has an ON/OFF lever or switch
  • whether the old switch has and external or internal unloader valve
  • how the power supply gets into the pressure switch and from the switch to the motor circuit

Answer all of the above and then Google compressor pressure switches and find one that's convenient to obtain and one within your budget.

One more thing...

I can't find the compressor pressure switch?

Fractional and small air compressors that have a tank have a pressure switch. Bet on it.

Those pressure switches will not look anything like those you've seen so far. This picture shows another type of compressor pressure switch.

Buying a compressor pressure switch -
This, too, is a compressor pressure switch!

Where is this one located? When you pull the cover off your small compressor, look for the ON/OFF switch. See the power line coming in from the plug? Follow the wire on the other terminal. It will normally go to the pressure switch.

Find a switch on line that looks similar, has the same pressure range, the same voltage, (ignore the unloader, ignore the ON/OFF lever or switch as they aren't on this type of switch) and find a match!

One more, one more thing...

If you have a question about your pressure switch you can certainly ask it here. I expect you'll get an answer quite quickly. Just be sure to click on the notification button so that you'll know when your question gets answered.