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Most of the time you have to do an air compressor repair only due to a faulty air compressor pressure switch. And having a faulty pressure switch from time to time is a natural thing.

Air Compressor Repair

So, doing an air compressor repair yourself is easy. Plus, replacements are available in stores and by using our step-by-step guide with instructional images it’s become a lot easier, safer, and cheaper.

Air Compressor Pressure Switch Unloader Valve Problem

The reason why a compressor won’t start is because of the faulty compressor pressure switch. The problem lies with the compressor unloader valve.

This unloader valve is built into the pressure switch. Having an unloader valve malfunctioning is one of the most common issues that compressor owners usually have to deal with.

The compressor won’t start up due to the trapped air inside the compressor as the motor reaches the operating pressure.

In normal conditions, the unloader valve kicks out the leftover pressure to start the compressor quickly. The unloader valve in this condition makes a “Hissing or Psssst” sound.

Air Compressor Repair – Compressor Unloader Valve Problem

My Air Compressor Just Hums Won’t Start, But Why?

On the other hand, due to a faulty unloader valve, the trapped air will not release and the motor against this great exerting pressure makes a humming sound.

This load of trapped air over the piston is enough to block the compressor from starting and your compressor continues to hum.

Why The Compressor Pressure Switch?

As you know, this small black box holds immense importance for your air compressor. Because it completes the entire circuit of your compressor.

It measures, manages, and controls the pressure when the tank pressure reaches beyond the set higher or lower pressure.

Tools Needed For Air Compressor Switch Repair

Below are the tools with their description that you need and why and where you need them to fix your compressor.

Heat Gun

The heat gun belongs to the class of versatile power tools. They are used in paint removal, welding, plumbing, bending plastic, DIY, crafting, and loosening up screws and bolts. It emits hot air usually within a temperature range of 100 to 500°C.

In our air compressor repair guide, we’ll use the heat gun for the outlet, pipe, gauge thread, and other joints. Because, in some cases, the joint due to the old compound doesn’t even move. So, the heat gun softens up the old sealant so it can easily be unscrewed.

Small Wire Brush

The small wire brush is used for cleaning out the rust, dust, and old sealants accumulated in the threads of tank pipes, safety valves, and other pipe joints.

If you don’t do it then the pipe thread sealant i.e., the Pipe Dope or Teflon Tape you apply will not be effective and the joint will not sit tight as it should be. This can also cause the ring to become free. In the worst case, compressor air leaks.

Needle Nose Pliers

These are special types of pliers used for handling mini-jobs where our fingers can’t reach. They are mostly used for handling wiring in tight places.

Here we’re gonna use the needle nose pliers for connecting and disconnecting the pressure switch wiring to their respective terminals. Since it is difficult for our fingers to do that.

Simple Wrench Set

The simple wrench set or also known as screw wrench has specifically sized wrenches used for screwing and bolting small bolts and pipe joints. Here we’re gonna use this wrench set for unscrewing the check valve, and tube fittings, and removing other small joints.

Ratcheting Screwdriver Set

The ratcheting screwdriver set is a multi-purpose screwdriver with different types of screwdriver bits. The bits are detachable and can be used for small screws and bolts.

Here we’re gonna use it for removing different screws and wire connections in the pressure switch.

Adjustable Wrench Or Slip Joint Pliers

The adjustable wrenches or split joint pliers are phenomenal hand tools. They have an adjustable jaw that can be used for removing and tightening up large bolts, nuts, and pipe joints.

We’re gonna use one of these to remove or tighten up the pressure gauge, pressure regulator, and switch assembly.

Pipe Thread Sealant (Pipe Dope Or Teflon Tape)

The pipe thread sealants are adhesive compounds specially used in the pipe joint threads for a tighter and more secure fit. These sealants remove joint leakage and the free joint problem. The most commonly used pipe thread sealants are Pipe Dope and Teflon tape.

How To Do An Air Compressor Pressure Switch Repair Yourself?


Below are simple and easy steps which you can follow to do an air compressor repair by yourself.

Time Needed To Complete This Project: 20 minutes

1. Before Repairing Air Compressor


Before you begin just check the tools that you need for your air compressor repair are there on the table:
1. Heat Gun
Small Wire Brush
Needle Nose Pliers
Simple Wrench Set
Ratcheting Screwdriver Set
Adjustable Wrench Or Slip Joint Pliers
Pipe Thread Sealant (Pipe Dope Or Teflon Tape)

2. You Should Wear Safety Gloves


Before you began to replace/repair the pressure switch you should wear safety gloves to protect your hands.

3. Turn Off The Compressor


Unplug the electric cord and also turn off the compressor power switch to avoid electrical shocks.

4. Air Compressor Safety Valve Ring


Pull the safety valve ring to bleed out all the tank air pressure to avoid any problems during unscrewing and removing the piping later on.

5. Remove The Air Compressor Pressure Gauge


Now, use the wrench set to remove the tank pressure gauge. Sometimes the old compound in the thread joints and piping causes them to stuck and they won’t even budge. So, here use a heat gun to soften up the compound and unscrew the joints.

6. Unscrew The Compressor Check Valve And Tube Fittings


The next step in air compressor repair is to unscrew the tube fittings from the check valve and pressure switch and remove the pressure switch tube.

7. Unscrew The Compressor Pressure Regulator Assembly


Now, use an adjustable wrench or slip-joint pliers to carefully unscrew and remove the compressor pressure regulator assembly.

8. Remove The Pressure Switch Cover


Use the ratcheting screwdriver to unscrew and remove the pressure switch cover. With a ratcheting screwdriver, you can change bits according to the requirement.

9. Disconnect The Pressure Switch Wires


Use the needle-nose pliers to unhook the two black wires from their respective terminals. Pull out the two big power cord strain reliefs. Now, Use the ratcheting screwdriver to unbolt and disconnect the two green wires from the pressure switch.

10. Remove The Compressor Safety Valve


Use the wrench set to unscrew and remove the pressure switch safety valve. If the valve won’t budge or unscrew then use the heat gun to soften it up a little bit.

11. Using The Heat Gun


Before you began to remove the whole pressure switch assembly use the heat gun on the tank pipe. Due to heat, the adhesive sealant compound will soften up and you can easily remove the whole assembly without applying any force.

12. Unscrew The Air Compressor Pressure Switch Assembly


Now, use the adjustable wrench or the slip-joint pliers to turn and remove the pressure switch assembly from the pipe. It depends on your compressor’s pressure switch assembly fitting that which type of wrench or plier can easily unscrew the assembly.

13. Removing Pipe Thread Sealant


Use the small wire brush to clean up all the dust/rust or old sealant between the tank pipe thread.

14. Apply, The New Pipe Thread Sealant


Now, apply the new pipe thread sealant on the tank pipe thread for air-tight fitting. So, the ring doesn’t get free.

15. Now, Replace Air Compressor Pressure Switch


Bolt up the repaired or new pressure switch on the pipe connected to the tank. 1st do it with hands so the pressure switch can sit right on the pipe without any tilt.

16. Aligning The Compressor Check Valve And Tube Fittings


Now, use either a wrench or slip-joint pliers to tighten the pressure switch. The added pipe thread sealant will firmly lock the pressure switch assembly in its place. Here make sure to align the tube fittings with the check valve.

17. Cleanup The Compressor Safety Valve Threads


Now, use the small wire brush to properly clean out any rust/dust particles from the safety valve thread and apply the pipe thread sealant to the safety valve threads.

18. Tighten Up The Safety Valve


With sealant, the valve can sit tightly in the pressure switch. Then use the small wrench to screw up and tighten the safety valve.

19. Reconnect The Green Wires


Use the ratcheting screwdriver to remove the outer cover of the new pressure switch and bolt up the previously disconnected two green wires to their respective terminals.

20. Insert The Power Cord Strain Relief


Now insert the two big power cord strain reliefs into the side brackets. Make sure they are fitted perfectly.

21. Reconnect The Black Wires


Use the needle-nose pliers to insert the two black wires into their respective terminals of the new pressure switch. Now, use the screwdriver to bolt up the external cover of the pressure switch.

22. Brushing Up And Applying Sealant


Again use the wire brush to clean the pressure regulator threads. Apply the pipe thread sealant again to the pressure regulator’s connecting pipe threads for a snug fit.

23. Attach The Compressor Pressure Regulator


Screw the pressure regulator with your hand. Make sure the tank gauge head is facing upward.

24. Reconnect The Compressor Pressure Switch Tube


Here use the wire brush to clean up the remaining thread joints and apply the sealant. Now, use the screw wrench to reconnect the disconnected pressure switch tube with the check valve and pressure switch.

25. Tighten Up The Compressor Pressure Gauge


Again here clean the pressure gauge thread with the wire brush. Apply the pipe thread sealant to the pressure switch gauge threads. Use the same old slip-joint pliers to tighten up the gauge firmly on the pressure regulator.

26. Finally, Start Your Air Compressor


Finally, plug in the air compressor electrical cord and start your air compressor to begin your work.

Air Compressor Repair FAQs

Q: What is an air compressor unloader valve?

Ans: An air compressor unloader valve is a small, mostly brass-colored part that is located with the compressor pressure switch. Its main function is to vent out the trapped tank air in the compressor to reduce the load on the piston so the motor can start again. It usually sizes up 4″ to 5″ in length/width.

Q: How to fix an air compressor that won’t start?

Ans: Your compressor not working due to a faulty check valve, pressure switch, or the motor pump itself. Replace the check valve, if there’s air in the tank and still air compressor won’t start. If there’s no air in the tank and still the pressure switch doesn’t start the pump motor then replace the compressor pressure switch. Finally, replace the pump motor itself, if the pressure switch is doing good but the motor is not starting up.

Q: Why is my air compressor leaking air?

Ans: Air compressor leaking problem is caused due to the check valves that failed to shut off completely. Leak in the air compressor oil cap or fill tube, you should verify the piston seals and replace them. And finally, air leaked out from the compressor hood caused by a faulty tank valve. It mostly happens in small air compressors.

Q: Why is my air compressor slow to build pressure?

Ans: Usually when an air compressor takes longer to fill it is due to a failing pressure/intake valve, due to a pump gasket, or a pump seal problem.

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