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How to modify a fridge compressor into a silent air compressor

Picture of 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.
 
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Step 1: How to remove the compressor from a fridge

Picture of 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.
This is a diagram of a NLY7F compressor. I'm having trouble figuring out which wire to connect to what. Can ye help me out? Thanks a mill. :)
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DonaldF219 days ago

Thanks for sharing these great guidelines. Everyone can go through http://aircompressorjournal.com/ to learn more about air compressor. Many thanks. Hope to see more tips in the future.

HVACPro1 month ago

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.

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)

en2oh5 months ago

that diagram showing what appears to be an outlet trap seems backward would it not be better to reverse the flow?as you currently have it, once the condensate/oil reaches the outlet tube, it will act as a siphon.

I am using this to build a high pressure bottle burster.

I am using this to build a high pressure bottle burster.

rimar20001 year ago
Very useful instructable. I am using one of these compressors since maybe 30 years. It has very high compression but very low flow. I use it only to inflate my bicycle wheels. I tried to use it to paint, but because of its low flow it did not worked.
antonc81 rimar200011 months ago

You could run it through a pressure switch to an air tank. The pressure swithc will shut off the compressor when pressure in the tank reaches a preset pressure, then will turn back on when pressure drops below another preset.

rimar2000 antonc8111 months ago

Thanks, antonc81.

kerimil (author)  rimar20001 year ago
You can also use air conditioning compressors - they offer a lot higher flow.
Thanks for the info, I didn't know that.
guys, if you do want to use refrigerant compressors, please contact your local HVAC technician about recovering the refrigerant inside. The ones that are extremely harmful are R-12, and R22. There are plenty more but in residential applications, these are it. R-134a is considered an HFC which doesn't have chlorine, so it has a 0% ozone depletion. But it's a greenhouse gas. For those wondering, 1 chlorine molecule can destroy 100,000 ozone molecules. So at least contact someone to recover these units.
LowEnergy1 year ago
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.
kerimil (author)  LowEnergy1 year ago
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.
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
agguilar1 year ago
hi, can i use a air conditioner compressor ? thank you!
kerimil (author)  agguilar1 year ago
Yes, of course you can. They are even more practical for everyday use than fridge compressors, because their CFM/minute is higher. I haven't ever built one because they are hard to get where I live but everything is pretty much the same. Here's one thread found on them - http://www.spudfiles.com/forums/i-have-an-a-c-compressor-to-convert-questions-t18828.html

There are like tons more examples there but be warned that the search function really sucks ;-)
Very clever use of more "throw away" stuff in our disposable society.