Intro: 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
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
Cord w/plug (junk TV I had)
Tennis ball ( with a few small scraps of rag)
Soldering torch w/solder
Small pipe cutter
Hot Glue gun
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.
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.