How to Modify a Fridge Compressor Into a Silent Air Compressor

Intro: 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

Comments

[warhawk8080]

Very neat...I drilled a hole in the bottom of my compressor, drained all the hydroscopic freon oil out of it..used a self tapping sheet metal screw to seal the hole...then used standard 10w30 motor oil as the lubricant in the motor...only used about 2oz (1/4 cup) to refill it...just let it suck it in thru the intake tube...if it got too much oil...it will blow it out the output line till it reached the required level
oh, by the way the freon had already vented from the line...this is why they threw the refrigerator out...

[Morris Runn]

(Ignore the “professionals” who say you will begin a thermonuclear meltdown by doing this)

if you turn the unit upside down the oil will flow out of the IN port (it does not connect to anything inside, just lets the air into the sealed housing). Mineral oil is what they used in “the old days” and is “food safe”. You can get just over 500ml from Walmart as baby oil for a couple bucks.

For a smaller water cooler compressor I drained about 240ml. I did a couple flushes of 250ml each to get all the old oil out and then added 250ml of the baby oil.

Since it was a reasonable size, I left the condenser coil and drier attached. (I am mainly going to use this with CO2)

i used 1/4” flare fittings because they are compatible with the cheap refrigeration gauges you can get on eBay (less than $30) that show vacuum and pressure to 500psi. My little unit has no problem getting up to 500psi. (Enough to liquify CO2 at a reasonable temperature)

Morris

[adambendror]

I am finding that a small amount of oil constantly comes
out the air outlet of the compressor. I understand that the oil is
needed to lubricate and cool the compressor. I am worried that
eventually the compressor will push all of its oil out. I also don't
want oil being pushed through the air line. Is it normal for this to be
happening? What is the best way to stop oil coming out? I am using the
compressor to bubble air through water so there is not a a lot of
pressure in the system..

[first180]

there is not much you can do to stop the oil coming out with the air other than add a water trap to the output to catch the oil/water as it comes out and add an oiler to the intake to introduce new oil. in its original sealed designed setup the oil that escapes from the output would just circulate the system and back into the intake.

[first180]

how hot will a fridge compressor run without damage? i drained the oil and filled it with hydrolytic oil, it runs fine but gets very hot after a few minuets, how would i work out what its max working temperature would be and any suggestions on case cooling in order to make it run continuously. even temperature controlled programmatically i don't like the idea of stopping and starting it if its to hot as that introduces the complication of failing to start under output load. im thinking of maybe sitting it on a thermal pad water cooled heat sink or the like, the bottom seems to get much hotter than the top, any suggestions on cooling would be appreciated.

[mark49]

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.

[shepvandelay]

the best advice. also old water tanks can make for bad air tanks if theyre rusty. always remember to drain your air compressor tanks regularly too, folks. thinking of.,. i need to go outside and do mine. she all sloshy

[donroi]

So now we have air under pressure in an oil mist and an electrical motor with the possibility of spark generation all in that sealed cylinder. Is that not a bit dangerous?Bearing in mind that most lubricating oils will burn hotter than and have a lower flash point than diesel.

[shepvandelay]

if you get a leak in the low pressure side of your fridge, itll let the refridgerant out and start sucking air, which will lead to rust and clogs on the high pressure side capillary tubes and soon enough your fridge compressor will be pumping on side to max with no cooling what so ever. people usually toss their fridge at this point. (i liek to fix emn) either way, they rarely blow up, as far as i know. and by rarely i mean never... never ever heard of a fridge dieseling and going off.

[robertgibbs2128]

I thought the hole in the ozone layer closed itself up years ago when the funding dried up to study it

[hemic2]

Fridge compressor has really high compression ratio and uses oil to lubricate the cylinder head. Air + high compression + oil = diesel engine. For those of you who make this, understand that there is some (small) chance that the thing will explode. Be safe out there

[DennisG]

This is great but, what happens to the two tubes that you show as being cut from the radiator attached to the back of the fridge?

[1111elektro111]

air compressor form the refrigerator-- oil
https://www.youtube.com/watch?v=3FKQzHvwxCw

[Yi Lingxing]

Hi, i just see this good share,but there is a question i want to ask,if the compressor from the one refrigeratior can be used in other ways ,for example ,another refrigerator which compressor was broken down?
if not ,i will consider to choose a new compressor online https://okmarts.com/compressor/hitachi.html
Could anyone can give me some idea, how to choose a fit compressor? thanks so much.

[H3xx]

I have a powered water bottle dispenser that puts out nasty, rusted water, but still has a working compressor, would that compressor work for this? I now live in a place with drinkable tap water and no longer need the dispenser even if it can be repaired.

Also, will a party helium tank work as an air tank? Since they're inexpensive and the gas inside isn't flamable or toxic?

[HVACPro]

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.

[mribble1]

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

[r01walker]

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.

[Gelfling6]

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)

[LowEnergy]

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.