How to Modify a Fridge Compressor Into a Silent Air Compressor

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Introduction: How to Modify a Fridge Compressor Into a Silent Air Compressor

Here is my how to on modifying fridge compressors into silent air compressors. They are ideal if you need:
+ 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)

I do realise you might have some problems with wiring - I'll make a video on it soon

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

Once you have the compressor running you need to find a way to securely attach a fitting to it's output tube. Of course you can just use a clamp and put a lenght of air line onto it, but that's not the best method - especially if you plan to use the compressor at more than 10-15 bar.

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

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    I just don't understand the drawing after the air comes into the 1/2" T what is the ball valve at the bottom for, is it to drain water?

    44 Comments

    It's important to note that if you cut the tubes you release the refrigerant. Old refrigerant is bad for the ozone layer...new refrigerants are not as bad for the ozone layer but they still are thousands of time worse for global warming than CO2. So to do this responsibly, you have to either get a fridge that has already had the refrigerant removed, or you have to find a refrigeration technician who can do that for you.

    Very cool to make good use of scrap--sorry to have to inject this note of caution.

    Yes, you are right. But freon hasn't been used for about 20 yrs so vast majority of fridges you will find won't have it. What's more, if you leave an old fridge with freon it will leak out the refrigerant anyway.

    Freon hasn't been used, but as I noted, new refrigerants are bad in a different way. But definitely don't just leave a fridge rusting in the shed, and don't put it in a landfill. Take it to get recycled. The refrigerant will get reclaimed.

    Sorry but you are completely wrong here.

    30 years experence, retired hvac service technician.

    Which part do you disagree with? The only part of this that you would experience directly by working as a HVAC tech would be

    "If you cut the tubes you release the refrigerant"

    Do you really dispute that claim?

    It is for y author
    I removed compressor from my old fridge .that time it was working
    But after words i droped by mistake
    It was tilted up side down
    Then after it is not working
    I tried a lot but it is not workingat al lhelp me out of this!!!.
    Plz......

    That's right--classic freon (CFC), which had the worst ozone layer effect, was phased out in 1995. If you find a 20-year-old or older junk fridge, that's what's in it. The main replacement used since then is HCFC. That has something like 10% of the effect on the ozone layer--not nearly as bad but still pretty bad. And there are HFC refrigerants now that have no effect on the ozone layer.

    However, all three--HFC, HCFC and CFC--are bad for global warming--thousands of times worse than CO2! So even if you do this with a fridge made in the last few years, it's a serious problem. In most places, there are programs to make sure fridges are safely taken care of, with the refrigerant collected. They'll pick up old ones for free, or even pay you for them. You can check in your area, or find many of the programs by zip-code here:

    http://www.jacoinc.net/recycleNow.aspx

    Never mentioned is the refrigerant in the system that will vent when the tubes are cut. It's against Federal law to purposely spill ozone depleting refrigerant. These domestic refrigerators do not have access ports for checking refrigerant pressure. Spraying refrigerant can frost bite skin and damage eyes. Be legal and safe.

    You must be very careful using home made compressors. I worked on a job several years ago where we used a home made compressor consisting of a belt driven freezer compressor, a pressure switch and a hot water tank used for air storage. The compressor was located in a garage under a bedroom. The pressure switch malfunctioned and the compressor didn't shut off resulting in a rocket that went from the garage through the bedroom and out through the the roof of the house. This sheared a section out of a 2X12 floor joist as it went. I often wonder how much pressure was built up in that hot water tank. By the grace of God no one was hurt. A safety pressure release valve is always a good idea.

    Get these type compressor pumps free!

    And, these free ones are better then the
    small fridge ones - go to a HVAC company and ask for an old compressor/pump
    from a HVAC heat pump.

    These are removed and replaced all the time and
    the HVAC company should have properly decommissioned units with
    refrigerant already removed and be happy to give you one as they just
    dump these in the trash.

    I once went to a local HVAC company and
    ask if they could sell me a decommissioned HVAC system heater for a green house,
    they took me out back and said here are 5 nice HVAC heater units, all
    work great, with fans, and you can have one or all for free.