Introduction: Making a Fridge Compressor Into a Vacuum Pump

Picture of 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.

Step 1: Finding a Fridge Compressor

Picture of Finding a Fridge Compressor

I found mine out back of a local Motel.

The unit is from a small bar fridge that is common in Motel rooms. Someone else had already removed the coil from the back so I could not scavenge that, but the coil and the coolant was gone.

Note: If the coil is still attached to the fridge there is a good chance that there may still be some pressure on the system, so be careful when cutting lines. There was also talk of oil spilling out of compressor, but mine did not spill oil, even when turned upside down.

I snipped the lines, leaving as much as possible, with a heavy set of side cutters I carry in the truck. The wires were cut as long as possible and the starting capacitor was unstrapped and saved.

What I needed besides was:

A power Switch w/face plate
Junction Box
Cord w/plug (junk TV I had)
Tennis ball ( with a few small scraps of rag)
Copper tubing
Vacuum gauge
Plastic tubing
Compressor Oil


Soldering torch w/solder
Small pipe cutter
Screw Driver
Hot Glue gun
Large syringe

Step 2: Maintainance

Picture of Maintainance

first things first. Clean all the pieces of the unit with a rag and some cleaner.

On the side of the compressor there is a diagram that makes it pretty straight forward what you are dealing with. There are the three tubes: In, Out, and Process.

Air comes in. Air goes out. Process is for the oil.

As I had heard so much about oil spilling out and mine did not I was a little concerned that the unit may not have any in it. I cut the sealed end off the unit with the pipe cutter, leaving it as long as possible. I then turned the unit upside down so the pipe drained into a collection dish. there was a good amount of oil in the unit, but it looked pretty dirty compared to new oil. It looked like a golden motor oil, where a new compressor oil is a water clear oil.

I marked the level of the oil on the container where the old oil rose to and stored this oil in another container for disposal. I then filled the first container to mark I had made, plus about 50ml more. I did not get a proper measurement, but will estimate a total of 250ml was put back into the compressor via a large syringe which extended into the process tube.

This tube then had the end squeezed down and soldered tight.

Step 3: Putting the Pieces Together.

Picture of Putting the Pieces Together.

One the out tube, I cut the squeezed end off and reamed out the opening for a good air flow. You will see that this opening is not very large, so bigger is better. (This makes me think that I should remove the small line altogether and just use the larger pipe - More CFM.)

I installed a piece of 1/4 inch copper tubing over the out pipe and soldered it in place. I then bent the pipe up to a level higher then the top of the compressor and installed the tennis ball.

The tennis ball is slightly modified by puncturing holes and being stuffed with scraps of rags before installation. It works as an oil vapor collector and muffler at the same time. The compressor is very quiet, but with the ball, there is no noise from it at all.

As a note, some people use these compressors as compressors for air brushing with paint. The install a proper oil collector inline and from this they run a line to the air brush for painting.

On the In pipe I just straightened the pipe out so that it ran horizontal and cut the squeezed end off with the pipe cutter.

I have gone a bit cheap on this section right now because it was late at night and the stores were closed, and I can.

I took a piece of 1/4 I.D. plastic and hot glued it to the pipe. It can be easily cut off later if desired, but will be good to run a few tests.

The wiring is pretty straight forward - follow the diagram on the box the switch came in. The wires run into the junction box, attach the wires to the switch, attach the switch to the box, then put on the cover plate.

The starting capacitor it left as is and should not be altered.

Step 4: Testing.

Picture of Testing.

For testing I made a 'T' fitting out of 1/4 inch I.D. plastic pipe and hot glue. The 'T' fitting was connected to the vacuum gauge and the other plastic tubing by 3/8 inch vinyl tubing pieces I had laying around.

It worked pretty good and held the air, but I can see it is not that strong for everyday use, and will be replaced with proper fittings when I get around to it.


I can get down to 27 inches of Mercury of Vacuum which is converted to 9.668 T/square metre. The pump can also hold this vacuum pretty good when switched off. I lost about 2 inches of Mercury in one hour. The pump also had no trouble starting with 25 inches of mercury vacuum on the line working against it. I am pleased.

Plenty of pressure for anything I will be doing. Maybe too much for some projects. There is a pressure switch I am looking at building that can regulate this. It uses a vacuum valve from a car and a power switch. It looks about the best for fine adjustments to the line vacuum output.

The problem I see at this point is the CFM is very low. I am not sure the exact amount but estimates are 1.5 CFM. This is where I think if I can remove the chocking line in the discharge path that the vacuum CFM may be increased.

Another option is a reservoir. This could be installed in parallel with the pump and used to make an initial large evacuation then the pump could take the chamber down to a final vacuum pressure if desired.

This is a rough finish with many things left to be done, but from here anyone should be able to modify the system to their personal needs and shop area. Hope it works out and happy vacing.

Step 5: Bigger IS Better

Picture of Bigger IS Better

If you can find one go for a bigger ROTORY compressor.

I found one in a great big, old deep freezer. The freezer itself was at least 5 feet long, maybe 6.

I wish I could have taken the whole thing, I would have made a solar drier out of it or something, but I don't have the room.

Anyway the compressor is awesome. About twice the volume in size, but three to four times the CFM. Just what I was looking for.

Also I ran the pump for about 30 minutes under full load and it was barely warm to the touch.

It still did not go past the -27 inches of mercury, though. Fine with me.


freddyzdead (author)2017-05-17

@strmrnnr I don't understand why you are concerned about what you call "CFM". There is no such thing when you are dealing with vacuum. The trouble is, you are trying to use a compressor backwards. So, the pump has to evacuate the whole enclosure before it can start giving you vacuum. That will obviously take some time. It will take forever to pull it down to 30 inches, if it ever does. The whole idea of CFM is kind of meaningless; what flow there is will get smaller and smaller, assuming there are no leaks. Eventually it will be next to nothing. I think there might be long-term consequences for the pump as well. The motor is normally cooled by the refrigerant coming from the evaporator, which we obviously don't have here. There will inevitably be some oil expelled, so you need to pay good attention to recycling it. I doubt the tennis ball will do a good job. I wouldn't expect much difference in time to pull a vacuum for the smaller compressor vs. the large one. Finally, 27 inches of mercury is not a very good vacuum. If that's all it will manage, you're wasting your time. This might be because the pump is working backwards to what it was designed for.

labdude (author)freddyzdead2017-06-04

Well, you noted that CFM is a measure of flow, and while meaningless for vacuum, it does bear on how fast it will pump down to a desired level. Add while 27 inches may not be a great vacuum, for many applications it is perfectly acceptable. We are not all trying to simulate deep space, or build a tokamak; for home science experiments, or stabilizing/dyeing wood blanks, 27 in/Hg is just fine.
I'd be more concerned about repeated use without proper cooling/lubrication. My understanding was that many A/C refrigerants have a lubricating component - or maybe was that mostly for auto A/C, I haven't messed with that since they used real Freon.

dagyboy (author)2013-10-21

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?

freddyzdead (author)dagyboy2017-05-17

No, but when my car a/c stopped working, I regassed it with LPG. Barbecue gas. Works just fine. I pulled a vacuum on it first. To do that, I BOUGHT a vacuum pump on ebay. Just under $100 and it works very well. I wouldn't have even bothered trying to make one from an old compressor.

zapro (author)2011-01-11

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 :-/

GroundingStick (author)zapro2012-06-20

CO2? Photosynthesis!
And compare IR absorption with the far more abundant H2O...


I have been thinking about this for a long time. It's unlikely you will read this after 5 years, but... Photosynthesis Indeed! Why is this never mentioned? Plants breathe in Carbon Dioxide. They breathe out Oxygen. And if the CO2 levels are increasing, could it have any correlation with the vast areas of jungle vegetation that have been cleared? Although, I have read that most of our oxygen is produced by ocean algae. But we are doing as good a job at ruining the oceans as we are the land. Plague species, we are. We just can't leave things alone. Anyway, I just can't sit with blaming climate change on carbon dioxide. It can't be that simple.

tinstructable (author)zapro2011-07-26

Why didn't you just pour it into a sealed container and go from there?

zapro (author)tinstructable2011-07-27

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 (author)zapro2014-03-20

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 (author)The Freak2014-03-20

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

long3465 (author)zapro2014-02-14

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 (author)zapro2013-10-14

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.

yotnomuk (author)2009-07-29

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

Skipper333333 (author)yotnomuk2011-06-20

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.

JohnM993 (author)Skipper3333332016-09-01

If ya using a reciprocating comp from an old fridge you don't need a check valve , comp will start up against that kinda pressure no problem there designed for it

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 :)

strmrnnr (author)yotnomuk2009-07-31

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.

yotnomuk (author)strmrnnr2009-07-31

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)yotnomuk2009-08-02

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 (author)strmrnnr2012-02-08

Where did you add the oil? Into the air-intake tube?

Deeg (author)Deeg2012-02-09

Nevermind, I'm a dork. I totally missed the maintenance step.

swander (author)2016-07-02

ISO 10 is the usual oil in consumer refrigerators and the pump i pulled from a 14 foot kitchen fridge (already cut by scrapper for coils) had a stroke of 4.99 cm3. You can look up all sorts of specs by google the pump number. Mine was an EMY-60HER. Sure R134a is bad for environment, but i think its the same stuff that is in duster cans or air horns. I think it is not regulated when used outside the HVAC biz?

petercd (author)2010-02-10

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.

MartinG40 (author)petercd2015-11-08

I know the post I am responding to is over six years old as I type this, but since there are still people (like me) reading this Instructable today I wanted to point out that damage to the grommets is NOT why fridges and freezers are transported upright. The system lubricant in a closed refrigeration loop is in the refigerant (same is true for your car A/C). Tipping a compressor from vertical can cause the refrigerant to foam, which can trigger a vacuum lock in the pump. When the pump has a vacuum bubble in it then it is not being properly lubricated and can fail either immediately, or at least prematurely. This is why when a refrigerated appliance MUST be tipped for transport you must leave it in its new location for at least 24 hours before switching it on. This delay allows the foam to dissipate so the pump won't be damaged.

MichaelM793 (author)MartinG402016-06-17

Would a compressor from a PTAC unit be suitable?

petercd (author)MartinG402015-11-08

My point was somewhat vague, its not damage to the grommets that I was concerned about, but the fact that the motor wont seat itself back into the rubber mounting grommets and subsequently beats itself to death on the casing from the vibration when running.

MartinG40 (author)petercd2015-11-11

Nonetheless, while your scenario is possible I guess, the reason everyone says not to ship refrigeration devices on their side is due to the foaming/lubricant issue, not anything mechanical. Enjoyed your Instructable though.

lukeyj15 (author)petercd2010-02-22

with the split system air con, do you use the outside unit, or the inside unit?

petercd (author)lukeyj152010-02-23

its usually the outside unit, with the noisy compressor motor, in it

smandal13 (author)2015-08-23


vectorization (author)2015-06-17

This is what I'm working with. NLY7F compressor. Having trouble figuring out which wires to hook up to a switch. Could ye help me out? Thanks :)

LinB1 (author)2015-01-04

how high above sea level do you live ? At best ( at sea level) you will only pull 29 hg


Lovot (author)2014-03-20

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.

sconner1 (author)2013-02-28

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.

downunderkid (author)2009-11-08

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?

zapro (author)downunderkid2011-10-17

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.grent (author)2011-07-26

How about using a water cooler compressor instead for low air volume containers?

golddigger1559 (author)2011-05-12

what kind of compressor was in it?

strmrnnr (author)golddigger15592011-07-10

The last one was an old 8ft long deep freeze.

jaaz95 (author)2010-09-19

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?

gummypaul (author)2010-06-28

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.

BobS (author)2010-04-21

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)BobS2010-05-01

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.

kelseymh (author)2009-05-06

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.

Lithium Rain (author)kelseymh2009-05-06

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.

higgrobot (author)Lithium Rain2009-05-06

I nominate Lithium Rain for today's Darwin Award

kelseymh (author)higgrobot2009-05-06

I'd invite her to the awards ceremony, but it's well known that the winners are always late. >ba-da-bing

lukeyj15 (author)kelseymh2010-02-22


strmrnnr (author)kelseymh2009-05-06

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.

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