Making a Fridge Compressor Into a Vacuum Pump

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Introduction: 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.

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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

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

Tools:

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

Step 2: 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.

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.

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.

Pressure:

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

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.

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    66 Discussions

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    krstecd

    Question 2 months ago

    Why you use capacitor on the compressor? when i took out the compressor from my old fridge it does not have any capacitor on it, i turned it on without and it works fine, should i add capacitor to my compressor and what capacity need to be ?

    @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.

    1 reply

    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.

    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?

    1 reply

    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.

    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 :-/

    8 replies

    @GroundingStick

    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.

    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...

    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).

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

    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.

    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.

    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

    5 replies

    Hi
    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.

    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 :)

    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.