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.
No, 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.
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.
The 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.
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.
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.