+ a silent compressor
+ a high pressure compressor
+ have little space and/or don't need a typical shop compressor
Typical fridge compressors are 100 - 300 watt units, deliver 0.7 - 1 CFM of air and can reach pressures over 500 psi.
Here is a video where I discuss the process briefly (I'll make a new one soon - feel free to comment or ask questions)
There are two ways to get a fridge compressor you want to turn into an air compressor:
A) buy a salvaged compressor
B) salvage one yourself from an old fridge
In case you choose option B then you have to remove the compressor from the fridge yourself - that process is described in the next step. If you already have a salvaged compressor then go to step 2.
Step 1: How to Remove the Compressor From a Fridge
Quite a lot of fridges are thrown out even though the compressor is perfectly ok. You can test it by plugging it in and the compressor should start. If that's the case you can proceed to wire, as shown here (requires an on/off switch all the other parts are already there)
In some cases the compressor is working, but its starting circuitry is broken - and the owner didn't knew it. I have experienced this on two occasions so it is not rare at all. You can test the compressor electrically using an ohm meter
Here is my video on how to perform this:
The pic below shows where to cut the copper tubes. You should always salvage as much of tubing as you can. It doesn't really matter what tool you use just make sure not to crimp the tubes - nice square cuts are preffered.
Don't forget to salvage the mains cable with the plug. Most fridges have a sort of junction box right on the side of the compressor as well as starting relay/PTC relay (all of it is house in a rectangular plastic enclosures you find on the side of the compressor). There will be a wire running from the fridge compressor to the inside of the fridge - it goes to the thermostat and powers the light inside the fridge - again the longer the lenght that you salvage the better.
Step 2: Finishing, Adding All Blows and Whistles ( Work in Progress - Sorry)
once you have the compressor and have it running you need:
1) way to connect the output tube (ie your air output) - ALREADY MADE A VIDEO ON IT (go to the last step)
2) an overpressure valve (ie a pop off valve - for safety reasons)
3) water/oil filter
Step 1 involves buying a pop off valve
Step 3 is covered in one of the pics - you might buy an off the shelf water oil seperator but my homemade filter works just fine
Step 3: Attaching to the Output Tube
Here is a simple compression fitting that can be build using just 2 male - femal fittings, 2 or more rubber washers and 2 steel washers. It's pretty straight forward -> the rubber washers are sandwiched between the two fittings and the entire assembly is put onto the output tube. Once in place you tighten the fittings and that compresses the rubber washers forcing them to form a seal around the tube.
Here's a video I've just made on this
The compression fitting holds onto it surprisingly securely - I have never had any leaks or problems with it. It's greatest advantage is that is servicable - meaning that you can untighten the fitting and remove it if you have to