Making A Fridge Compressor Into A Vacuum Pump

I have wanted a vacuum pump for some time, but I refuse to pay the price for a new one that looks of sufficient strength and duty that I imagine I need.

I have read in different forums about the making of a vacuum pump from a fridge compressor, but with the mixed reviews I was reading I was a hesitant. I am glad I finely did. What a nice unit. I have not used it for any applications yet as I just completed the unit yesterday and have been testing it.


In an attempt to produce more airflow (CFM) I broke this vacuum. I am glad I have started to find these for free. I tried to drill out the discharge to see if I could get more air flow. I have to say don't bother. The line inside is far more restricting and what a pain in the arse to fix, and still have it not work.

The new pump I found is not as good as this one, but should still work for my needs. I will be keeping my eye out for another.

If you are hunting for one look for a compressor with the starting capacitor like this first one. The only real difference between the two compressers I have is that the first had one and the new one does not, and the new one seems to have a hard time starting against the higher pressures.
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Lovot4 months ago

The reason for the low CFM is a very small displacement piston, which is excellent for high pressure low volume applications. The compressor I am messing with easily pushes 500PSI (Then the seals on my pressure hose started to blow, after that). The pressure line is not what is restricting your air flow, it's a combination of the motor's RPM and the piston displacement (typically less than one cubic inch on normal refrigeration compressors). I have taken a few broken compressors apart in the pursuit of knowledge.

Vacuum pumps are usually two stage pumps, which means they have two pistons connected in series to obtain a high vacuum. Refrigerator compressors normally only have one piston. Another factor in the amount of vacuum a compressor can obtain is how well the piston seals, and it's compression ratio.

zapro3 years ago
You REALLY should not open up a sealed system and let out the refrigerant to the atmosphere. Even R143a is 30 times as harmful as CO2 for the environment, and in some states you will get a BIG fine if it is found out that you let out refrigerant. Just keep this in mind.. I had 3 portable aircon's i'd like to disassemble for the compressors, but as i could not find anyone who was willing to recover the refrigerant i ended up giving them away for their intended use :-/
Why didn't you just pour it into a sealed container and go from there?
As it is a pressurized gas-system, you cannot just "pour" it out. You need to get a piercing valve, clamp that onto on one of the refrigerant lines, then get an empty gas canister, vacuum it out and then connecting a recovery pump between the canister and the appliance you are emptying from refrigerant. (An old refrigerator compressor will do just nicely, too) I do not have the equipment, and nowhere to turn in the refrigerant for reclaiming. Putting refrigerant back into containers not inteded to do so is penalty by fine too, so it's only for the professionals. This is partly because you can suffocate from R134a, since it's heavier that air, and does not smell at all, so you suffocate without even knowing it before it's too late. Another is the environmental issue, which isn't to be overlooked...
The Freak zapro4 months ago

Mine had R600a in it, which is methylpropane (also named isobutane). Flammable, but other then that pretty harmless compared to the old stuff (in my oppinion).

zapro The Freak4 months ago

Yep, the new ones have R600a in them, which you can safely vent outside. There is no interest in reclaiming it.

long3465 zapro5 months ago

One of the side duties my father has at the trash processing
facility where he works, is that he drains the fridges or anything that uses coolant.
I am not sure what the charge but, he does it a lot, during and after summer time.
The separate out the 3 main types and can sell that to someone who does who
knows what with it. But my point is, find the yard where the process fridges,
you notice them when you see hundreds of sad broken fridges. Ask if the guy who
does coolant collection in the fridges is working and ask them.

LowEnergy zapro9 months ago
Thanks for that note. Really important. If you can get one that has already had the refrigerant reclaimed, it's safer for you and the environment.
CO2? Photosynthesis!
And compare IR absorption with the far more abundant H2O...
dagyboy9 months ago
i just wondered if anyone on here has converted a 240 volt chest freezer into a propane gas freezer???? yes i know they can be bought online, but they require you buy bulk. so has anyone tried it?
sconner11 year ago
My harbor freight vac pump only does -30 inches and it cost $160.
I bought it to pull a vacuum for the A/C system in my car.
I'd never thought of using a reclaimed refrigeration pump for air.
And I always thought the sealed tube end was to fill the refrigerant.
Vac pumps as tools are expensive.
I never understood why, now I know there's no excuse for it.
yotnomuk5 years ago
i've got a couple ofquestion. im using a fridge compressor to replace the motor on my 1.5 hp 3 gallon craftsman so that the whole setup is quieter, the switch turns on below 90 psi and off at 125 psi. the question is , do i need a starting capacitor for this setup and should i put a check valve on the "out" line so that the pressure in the air tank does not back up to the compressor? thanks
strmrnnr (author)  yotnomuk5 years ago
I can't be of much help here as I have been dealing mainly with the vacuum side of the compressor. I do have some questions for you though. Are you really able to reach those pressures and how long does it take for the 3 gallon take to get there? I would have said that the arrangement would not be up to par as the fridge compressors are only 1/3 to 1/2 hp and the CFM seems pretty low. People are able to use them for low volume air brushes though so it would all depend on your application and unique situation. As far as the starting capacitor goes - it is best to have a compressor that does have one. I went through 4 compressors before I found the biggest one I have now. They all acted differently. Without the capacitor the pumps most of the time did not start against a higher vacuum. With a capacitor they start fine at all vacuums. The check valve would be safest, again, depending on your situation. On the vacuum side the vacuum holds for over and hour - drops about 2 inches of mercury in the hour.
I started this project after watching this video and it looks very promising. thanks for your help. just have one more question, what kind of oil do i use to replace the compressor oil, are they common in hardware store(home depot/menards)?
strmrnnr (author)  yotnomuk5 years ago
Home depot should have some. I picked mine up at Canadian Tire. It is a common oil for air compressors. It is in a bottle like motor oil, but the oil is clear as water when new. It will turn a golden motor oil color as it wears.
Deeg strmrnnr2 years ago
Where did you add the oil? Into the air-intake tube?
Deeg Deeg2 years ago
Nevermind, I'm a dork. I totally missed the maintenance step.
As far as the capacitor goes the one already on your unit should be fine. And a check valve is always needed to separate the tank from the compressor. Otherwise the pump is too hard to rotate and may not start (trip breakers or stall).
When the compressor gets up to pressure (cut out) and shuts off, the line from the pump to the tank will bleed down its pressure through the pump allowing the pump to start easier.
I used to repair air compressors.
Or you can get valves which I think are called something on the lines of an unloading valve which sits between the tank and compressor so that as soon as the compressor stops the tank is sealed and the air line bled. If you ever listen to a compressor that is what the sharp hiss is after the motor stops :)
This is a great instructable.
I have managed to find an old deep freezer that still works with coils attached - Was wondering how to remove the coils?
You cannot do this. You'll let out the charge of refrigerant, and it's very bad on the Ozone layer. Find a compresser elsewhere... (see my earlier answers further up etc.)
joe.grent3 years ago
How about using a water cooler compressor instead for low air volume containers?
what kind of compressor was in it?
strmrnnr (author)  golddigger15593 years ago
The last one was an old 8ft long deep freeze.
jaaz953 years ago
k mine didn't have a wiring diagram on it. so how do i wire it up? it has the two main black coards for main power, then 3 red, white and blue wires that i have no idea what they do. also how strong of a capacitor do you need to start it?
gummypaul4 years ago
I made one of these last week to use to pull a vacuum on automotive a/c systems. Works great. I've heard these should not be started under vacuum as it puts a strain on compressor. Don't know if its true but I put a tee on it with a small valve in case I have to turn it off and back on.
BobS4 years ago
As I understand, one unit would be able to suck the air out to about 1/30. Putting 2 in series would theoretically result in a vacuum of ca. 1/900 (about 1 mbar).
 Of course there are losses. What could be the pressure achieved?? Would adding a third stage still improve the vacuum?
strmrnnr (author)  BobS4 years ago
I do not think that you can get below 30 in merc.  unless we change the laws - the world is changing though so give it a shot. Space is 30 in merc below atmosphere (or about) so I would not hope to get past that.

The unit I have gets to 28, which is -14 psi. The combination of units will only get you there faster and maybe a little past.
petercd4 years ago
I have found the small fridge type compressors to be unsuitable for this sort of application, usually  the connecting rod breaks because its only spot welded onto the "big end" bearing.
Internally, the motor rests on rubber grommets, so tipping it over onto its side usually trashes the compressor. ( the reason why fridges are only transported vertically )
However the main problem is that the refrigerant and oil mix which keeps the motor from burning out in its original setting, can no longer fulfill its function once the motor is hacked from the fridge.
Thus its lifespan is very limited.

A much better idea is to use a rotary piston compressor like that used in split system aircons.
These rotary piston types have an accumulator tank to store the oil and don't spray an oil mist over everything, also these pumps include a thermal cutout on top of the motor housing, and a plus factor is that the field coils/motor is welded to the casing, so no tip over problems.

I picked up mine at the scrapyard and it worked fine, I bought some compressor oil ( Reflo 68A ) from a specialist aircon supplier, and its been running sweetly for 4 years now.

DAEWOO fridge compressor.jpgmatsushita rotary compressor.jpg
with the split system air con, do you use the outside unit, or the inside unit?
its usually the outside unit, with the noisy compressor motor, in it
kelseymh5 years ago
Very nice! Not everyone on this site is electrically experienced (or competent). If you could, I think it would be very helpful to expand your Step 3 (or add steps between 3 and 4) which include some closeups inside your Handy Box, showing the wiring connections to the switch. You might also consider (for safety :-) using a plastic quad-size Handy Box to enclose the startup cap as well, and then run the power cord out through a grommeted and strain-releived knockout.
Stuff and nonsense, it's not that complicated - the red wire and the black one do exactly the same thing, it doesn't matter if the main is on or not, and people who tell you to check the voltage are just wusses.
I nominate Lithium Rain for today's Darwin Award
I'd invite her to the awards ceremony, but it's well known that the winners are always late. >ba-da-bing<
strmrnnr (author)  kelseymh5 years ago
I can do that, but I think i will wait until I get a proper three prong plug, cord, and a mouting board I like. then I can add a couple of steps.
photon3034 years ago
You need to have the coolant inside the fridge removed by a professional. Most of the old fridge have coolant that are pretty bad for the ozone layer.
Nice job! A couple of tips from my experience:
I use a similar setup for vacuum bagging carbon regularly. To get the bulk of the air out I use a standard shop-vac. Pulls the mass of the air out in seconds.
As a reservoir, I use an old fire extinguisher. By adding two T-valves you can hook up both ends of the compressor to it and switch between pump and vacuum. Put the manometer and vacuumeter on the input of the valve otherwise you will pull a vacuum on the manometer, which will ruin it.
When using as a pump, add a filter to the vacuum side to prevent dust from entering. Dust will kill the pump very fast.
Use a mechanical timer to switch it on and off every 15 minutes. If you pulled a full vacuum and the system is otherwise sealed, this is enough to maintain the vacuum without over-heating.
mobolised4 years ago
It depends on what refrigerant the compressor is running on, probaly R22 and there for it needs a heavier oil which is a thick and colden but if it is R407 it should run on 3MA oil which is ligher.
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