Buying A Compressor Pressure Switch
              - continued

This is page two of a step-by-step process to finding the right replacement compressor pressure switch for your compressor. If you wish to start reading from the beginning, page one of Buying a compressor pressure switch is here.

We left off on page one talking about the things you may find hanging on the sides of your pressure switch. The first was the ON/OFF switch or lever. That's covered on the preceding page.

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.