Air compressors are extremely useful tools. But as you may have found out, they are not cheap. So, if you need an air compressor and can’t afford to buy one, then you need to know how to build an air compressor.

Building an air compressor is a relatively straightforward DIY project as long as you have some low-level experience in a few other fields.

To be able to build an air compressor, you must first already have some experience in welding and general carpentry. It’s also good to have some electrical knowledge as you will be working with exposed, high voltage wiring. 

Building an air compressor simply amounts to using a compressor motor to store air in a tank in a controller manner using a pressure regulator. Most important aspects of building an air compressor are controlled and taken care of by the regulator. So, all you really have to do is wire everything up and attach the air hoses properly. 

In this article, we will provide you with a general guide and outline to build a DIY air compressor.

Parts Needed To Build An Air Compressor

The first thing you need is a way to compress the air. If you are wondering how to build an air compressor, one of the most common ways to do that is to use a compressor from an old, discarded refrigerator or air conditioner.

These compressors are used to compress a refrigerant, but they are also more than capable of compressing air. 

NOTE: It’s important to purge the refrigerant from the compressor correctly. If you are lucky, whatever AC compressor you find for this project will already be empty.

If it’s not, however, you must pay a professional to properly capture the gasses stored in the tank. Do NOT purge those gases to the atmosphere. Doing so is breaking the law in just about every developed nation on Earth. 

The other main component needed to make an air compressor will be the tank the compressed air is stored in.For this, you can use a standard 20lb propane tank or a refrigerant recovery tank. 

One of the best things about using an AC or refrigerator compressor to build an air compressor is the fact that type of compressor is specifically designed to run quietly. 

You will also need a pressure switch. When it comes to a home-built air compressor, there is really now way to build one without a pressure switch.

This part is essential the brain, ECU, or controller of the entire machine. While they are not the fastest compressors, AC compressors are among the highest power. 

So, while they may take a little longer to fill an air tank, it can do so with much more force than a traditional air compressor motor and could blow up a tank.

For this reason, you absolutely must have a pressure regulator. It’s the difference between ‘How To Build An Air Compressor’ and ‘How To Build An Air Bomb.’

How Do I Find The Inlet And Outlet Of The Compressor?

The best way to determine which one is the inlet and which is the outlet is to turn the compressor on and see which line blows and which line has suction. You want to cut all the copper going in, other than the oil fill tube which will already be crimped off.

Other Components Needed For DIY Air Compressor

To build an air compressor, you are going to also need a start capacitor, a power cord, a pressure relief valve and a couple pressure gauges. You are going to need to know the pressure of your tank and the pressure of your tank’s output, so you need two of those. 

An air filter is also needed. A tank drain valve is essential because as you take a volume of air and put it in a smaller space, whatever moisture that was in that air becomes concentrated. Various ¼” inch pipes. You will need some way of coupling your home-made air compressor to a hose, so for that you can get a quarter quick coupler socket. 

The AC compressor will usually have three wires. If you are lucky, they are labeled as ‘run’, ‘start’, and ‘common’. As with any inductive load, the startup is going to take more energy than running. On startup, different windings are used in the motor as compared to when the motor is running. 

So, most AC compressors have a built-in relay that will switch power from the start wire to the run wire once the motor gets going. Common is the motor’s ground connection. Attach your run wire to one side of the start capacitor and your start wire to the other side. 

WARNING: It’s important to drain the capacitor. If you are not using a brand new start capacitor, then it could still have a lethal amount of charge stored inside it. While in most cases if you shock yourself with a fully charged start capacitor you won’t die, if you have a heart condition or just particularly unlucky, you could. 

NOTE: While most capacitors do have a polarity, the type of capacitor used in an air compressor does not. So, that means that in this case, it does not matter which side you hook into the capacitor. 

Add handles on the side. Lots of air compressors are missing a mechanism to store the cord.

When you are building a home-made air compressor, make sure to temporarily plug the ends of the AC compressor after you test it to prevent any dirt, dust, or anything else getting down in there.  

Prepare The Tank For Compressor Installation

If there is any kind of top or handle installed on your doner tank that you are using to store the compressed air, make sure to remove that. To do this part you will need a grinder or some other heavy-duty cutting tool. 

Also, make sure to sand down your doner tank to give it a nice, smooth finish. This part is optional, sure, but if you are going this far, you might as well make it look nice. Also, sanding and painting or otherwise finishing your tank will protect it from rust. 

All the connections that need to be made to your home-made air compressor will conveniently run through the pressure regulator.

So, you only need to make one hole and one connection to your air tank. To do that, simply drill, tap, and connect the pressure regulator to the tank using a quarter inch threaded pipe. After that, install your moisture drain plug in the bottom of the tank. 

You will need some quarter inch high pressure hose to make all of your air compressor’s internal air connections. Also, you will have to flare out the ends of the copper tubes coming from the AC compressor in order to properly mate them to the flexible air hose. 

The good news is, this is easy to do without any kind of special tools. Simply take a phillips head screwdriver of an appropriate size and gently push it into the copper tube while twisting back and forth. Continue this process until the copper connections are sized correctly for your hose. 

A simple air filter can be attached to the AC compressor’s inlet and soldered to the side of the tank. 

NOTE: For any part of this project that requires threads. You must use PTFE tape to create a perfect seal. Without PTFE tape, it will be nearly impossible to get an air-tight seal.

Most air tanks already have some mechanism to stay level. So, you more than likely won’t need to add any feet to your tank to keep it stable. 

Create A Platform For Your Compressor Motor

The next step is to find or create some sort of frame to attach to the top of your tank. This is where the AC compressor will sit. The easiest way to do this is to take a flat sheet of metal and bend it in a 90 degree U shape. After that, weld it on top of your doner air tank. Now you have a platform for your AC compressor. 

Once you have the above, simply drill 4 holes in the top side of the U-shaped plate and mount your AC compressor with rubber grommets. 

Paint And Finishing Touches

A simple can of spray wait will do just fine to give your custom home-made air compressor a nice, official look. It’s important to use lock nuts and lock washers when you are building your air compressor. 

Remember, it’s an air compressor! So, that means this machine will be vibrating quite a bit for extended periods of time. If you don’t use lock nuts and lock washers, at some point it will just shake itself apart. 

Conclusion 

Making an air compressor at home is pretty easy to do if you have a little experience in the related fields needed to do so. You need to be able to weld to be able to do this, but that is really the only hard-requirement.

Everything else involved can be learned on the spot, really. Just keep in mind that you will be working with high voltage wiring, so it’s good to have some basic electrical knowledge.

When it comes down to it, all that is involved with building an air compressor is using a compressor motor to put air in a tank. The good news is that all of the house-keeping tasks such as turning on and off the compressor motor are taken care of by the pressure regulator module.