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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    46 Discussions

    I am a licensed refrigeration technician and I notice that you fail to
    mention that this is both ILLEGAL and DANGEROUS. Pressures inside that
    system when the unit isn't operating can reach well over 100PSI and when
    you cut any of those lines that refrigerant will flash off into a gas
    and this will cause an extreme temperature drop and the result will be
    instant frost bite if it contacts your skin. You cannot, by law,
    intentionally vent any refrigerant into the atmosphere. You state here
    and other places that the "freon" used today isn't as bad for the
    environment and that is wrong on every level imaginable. Refrigerants
    used in low temp equipment are going to be either R22, R134a and in
    some cases R404A. These are NOT environmentally safe substances and
    therefore are regulated by the EPA. In fact R22 has been phased out
    because of this. Venting carries a hefty fine and rest assured this will
    be reported accordingly.
    Furthermore, using a refrigeration
    compressor as an air compressor isn't very wise. The unit uses the
    actual refrigerant, that you illegally removed, to cool the internals.
    The oil that is inside the system is considered hazardous waste.

    3 replies

    134 a is not regulated it is able to be bought and sold without a epa certification and has an ozone depletion potential of 0 % according to epa regulations 404 is also 0% 134a has gwp of 1600 404 which is not used in residential refrigeration has gwp of 3300 the new replacement for r22 which is 407c has1600 gwp and they say its safe enough to be used in residential sysems replacing r22 a so quit being a debbie downer and get ur info straight before u start being epa police cause I know in the 20 years i have done hvac service it is near impossible to recover 100% of any refrigerant from any system and the epa requires up to 90% recovery from any equipment if compressor is operational & 80 % if not operational so leave these people alone cause im sure in the time u have been doing hvac u have vented off more than what is recommended by epa just by taking ur hoses of the service valves. And if u think freon destroys air what do u think factories and cars are doing u dont see people dogging u for driving let them be

    i agree in part. the oil is special in that it will not mix with the refrigerant. their are other non wax based oils that can be used. as far as heat. which is a big issue. i suggest using aluminum heat transfer vanes. the outside housing is powder coated. and that will need to be sanded off. but the vanes could be soldered to the compressor. they do take lots of heat in manufacture. these compressors have been known to run 30 years and be beat all to ____. and still go strong.

    Actually, R134/a (is BORDERLINE Environmentally safe, as most 'Air Duster', Sports Horn, and Even most aerosol products are pressurised with it.. But I well understand your concern, having been a Firefighter/Haz-Mat-II warm-zone first responder.

    To the author, I also would HIGHLY suggest bringing a salvage refrigerator to a HVAC contractor, to have the refrigerant safely extracted. (vacuum pump system) (since it could be R12, which is still illegal to vent.) and leaving the system sealed at least 20 minutes before allowing venting to the atmospheric level. I haven't read further into the instructable, But also drain as much of the refrigerant oil as possible, and replace it with air-compressor oil, which will not foam, and cannot be contaminated like the refrigerant oil does. (But NEVER more than the amount you drain! as this will get oil into the output air.)

    One note to HVACPro, Not entirely unwise, as most compressors are essentially the same inside, as air-cooled, and using the Air Compressor oil will also provide cooling, carrying the heat to the metal case.. The thickness of the case is usually adequate incase of seizing/exploding. (as long as the case remains welded!) I've seen plenty of videos of converted compressors, and 'Exploratory Autopsies' of failed compressors to know the case is there for a reason. (especially one of a dual-compressor outdoor system, where the crank arms on a 6-cyl. Compressor failed, and shattered inside. Resulting, eventually burned-out the 2nd compressor's windings)

    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.

    6 replies

    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.

    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?

    0
    None
    mark49

    1 year ago

    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.

    Hi,

    I built a small fridge compressor and is running fine to load air in to tank. I set it to cut in in about 5 bars and cut out 7 bars. Its load in the air fine but when reach cut in 5bars should starts but it doesn't. I think its happens because its too hot and need to cool down. Any idea how to fix it? Ideal will be cut out 7 and cut in 6. Also I notice when using airbrush nad compressor is running, it struggle to load air in to the tank. Any idea how long fridge compressor can run continuously before break?

    Thanks.

    3 replies

    often the problem is not that compressor needs to cool down but rather that it cannot start against the head of pressure. It is best to use an unloaded valve so,that the line between the compressor and tank is empty when it restarts. To do this you need a one way valve in the plumbing to prevent unintended back flow

    Your site sucks and it's nothing but spam.

    SPAM!

    Hi,

    if the unit output tube's diameter is right (8mm, 6mm etc.), you can possibly get rid of the whole compression fitting and use standard plug-in fittings for plastic tubes. I did it on my compressor and it works like a charm, no leaks. Just clean the output tube with sandpaper and cover it with a thin and uniform layer of solder, which will prevent the fitting from slipping off.

    My compressor has a 5 liter tank from a cheap Stanley portable compressor and it's good enough for pumping tires or blowing the dust off. Working with air tools or painting is out of question, of course :).