Replacing A Compressor Pressure Switch

We recently had the need, and stumbled through the process of, replacing a compressor pressure switch on one of our air compressors.

There was nothing wrong with the switch itself. The problem was that one of the fittings that entered the manifold base of the pressure switch had cracked the base, and it was continuously leaking. In removing the pressure switch to replace the base, we found that the base itself was part of the switch, meaning that we had to replace the pressure switch. Here’s what the disassembled pressure switch  looked like after we had removed it from the compressor.

Replacing a compressor pressure switch - pressure switch disassembledNo, we are not interested in trying to reassemble this pressure switch. We expect the folks that build them are good at it, but the time it would take us would cost far in excess of what a new switch would cost, so we are obtaining a new one. Since the base is part of the switch and nowhere can you find a separate base, we would have to get a new switch anyway.

Here’s a look at the compressor with the switch removed. The fitting on the left is where the unloader valve line connects, and the vertical nipple on the right is where the pressure switch is mounted on this small DIY air compressor. The copper line sitting on the tank is the unloader line which connects from the tank fitting / tank check valve on the left over to the unloader valve on the pressure switch itself.

Replacing a compressor pressure switch - pressure switch mounting point on my compressor Now we want to remove the wires from the switch itself. There are two sets of wires. One set comes into the pressure switch from the motor, and the other set comes into the pressure switch from the supply side – the cord that you plug in to the wall socket.

We continue by removing the various wires from the old pressure switch connections.

Replacing a compressor pressure switch - the terminal connections inside the pressure switchThe power supply wires on this compressor are the black wire one of which comes from the cord to the plug, and the other is from the motor.The white wires, one from the power cord and the other from the motor circuit are the return wires.

The black and white terminal connections inside this switch are show in the image above. When this switch trips, power flows on one of either side of the switch, so, on this switch, both black wires are on one side, and both white on the other. As the switch works, alternatively, the black wires will be live or the white return wires will be live. Other switches may work differently, and you will need to read the terminal mounts to see what wire goes where.

The terminals will typically be marked motor or load.  That’s where the wires from the compressor motor are attached. The other wire terminals may be marked supply or power and that’s where the wires from the power cord are attached.

This next image is of the green wire mounting locations on this switch. The green wires are the ground wires and must be attached to a metal part of the pressure switch. One of these green wires from the power cord and the other is from the motor wires. It doesn’t matter which green wire goes in which of these two spots in this pressure switch, as long as both wires are attached to the proper ground point.

Replacing a pressure switch - pressure-switch-ground-wires

Continue replacing the pressure switch by removing all of the wires from the old switch.

Part of doing that will mean that you will have to disassemble the strain relief fittings As the wires enter the pressure switch they are held in place by these strain relief fittings. These hold the wires securely to help prevent a disconnect should either wire be pulled on aggressively. Typically there is a plastic nut inside the switch housing that has to be removed, as  is shown on the right in the image above unthreaded, and on the left, still threaded onto the strain relief fitting. Both plastic nuts will have to be removed.

The image below shows both wire sets – the ones from the power cord and the set from the motor circuit, removed from the pressure switch, and sitting on the compressor tank. You can see the rest of the strain relief fittings on both sets of wires.

strain relief fittings on pressure switch wiresWe will have to remove the rest of the strain relief fittings from the two wire sets. Reason being, we obtained a replacement pressure switch that has integral strain relief fittings.

The new one is also a pressure switch  that has the unloader valve built into it, rather than having it hanging on the side of the switch as the old one had.

More right here on replacing a pressure switch.

Comments

  1. Thanks for your good instructions for replacing the pressure switch on my compressor. My only problem is that I cannot work out how to remove the cover on the old pressure switch to access the connections for releasing the wires for transferring them to the new pressure switch. I tried every which way to get the black cover off to expose the wire connections, but it would not budge. I suppose I could break it open, as I will be replacing the whole unit.

    Please assist if you can

    Thank you

    • Odd that, David. No recessed nut on top, no edge locks where the cover extends past the base, nothing? Wish we could see that. In any case, you are right, since you are replacing the whole switch, have at the cover and see what you can see when you dislodge it. Just don’t cut any wires until you see what’s what.

  2. Hi, I was about to order a pressure switch on eBay and was wondering what you recommend using on the thread when screwing it onto the actual tank? I’ve been told not to use the white plumbers tape but to instead use a ‘High Strength Threadlocker’ type adhesive, or even ‘Locktite 242 blue’? Does it really matter? I’m from Australia by the way, your site is very helpful, thanks so much!

    • Anthony, the reason that tape sealant isn’t generally recommended for sealing threads on air fittings etc. is not because it doesn’t work, but we think it’s because folks can be a bit careless when they install it. If the tape is threaded onto the fitting in the direction that the thread is turned into the air port, the tape will stay on the thread. If careless in installing thread sealing tape, and a bit of that tape gets into the air stream, it can block air paths in any devices the bit of tape is blown into. If a paste sealant is used, and care is taken with its use, once it sets up, it can no longer be blown into the air stream.

      Thread sealant tape really doesn’t, in our opinion, provide sealing properties. The tape acts like a thread lubricant, allowing the fitting to be turned further into or onto a mating thread, developing greater thread to thread contact than would be achieved without using the tape, and a more air tight result.

      Thanks for your kind comment.

      As far as we are concerned, use any method you wish. Just be sure nothing can get into the air stream to foul up downstream equipment.

  3. Bob Beale says:

    My last compressor cost me $163.00 for a replacement switch and fitting (Aus) with this info from this page i bought 1 for on Ebay for $16.00 and fitted myself, works great Thank You. B.B.

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