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I'm attempting to convert a fridge compressor into a vacuum pump, but it got me confused. There should be one inlet and one outlet I believe, but instead I have three, with the third being connected to the second (the white one) through a thin copper tube with the bulky thing at the end of it (see picture). The white tube is the suction, it has a label on it. How would I hook it up, what are the three tubes for? (Sorry if it's in the wrong forum)

The three pipes are on the right

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The small tube I believe is for the freezer coil, or it could be a capillary tube (thank you Swift). Regardless, simply solder it shut and use the two larger lines for pumping.

I would like to note, this style of compressor cycles some of its lubrication through the refrigeration system, so keeping the crankcase full of oil is important since any oil lost during pump down has no chance of being recovered since this will no longer be a closed system.

That being said, it is possible to use these as a good pump. I used to run (and still have) an old refrigerator pump that had a separate oiling system sight tube that made for a great vacuum pump. These style of compressors are easy to spot (although not terribly common).

Running power to the unit needs to be done correctly. Typically black is hot, white is neutral and there is usually a green screw for ground. If you are unsure how to do this, find someone who is rather than messing with it as the wires need to be tied correctly to avoid risk of electric shock.

Good luck with the project!

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  • $\begingroup$ I don't think the small tube has anything to do with a freezer - it looks like a capillary tube to me brighthubengineering.com/hvac/… $\endgroup$ – Jonathan R Swift Jul 9 '18 at 7:22
  • $\begingroup$ Hi, thanks for the answer, I disassembled the entire fridge and figured out that the two are connected, and I forgot about this post. But you're right about the complicated wiring. Would you be able to give me some pointers? What confuses me the most is that there are two blue wires going to the relay. How would I control it with an SPDT relay (if possible)? $\endgroup$ – Peter Poláček Jul 14 '18 at 18:36
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One inlet (suction), one outlet (delivery) and the original filling point.

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  • $\begingroup$ By filling point, don't you mean the sealed-off pipe? That one is on the left, I have three other pipes. $\endgroup$ – Peter Poláček Jul 7 '18 at 10:38

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