Some years ago I made a good little vacume pump out of an old refrigerator compressor. It would pull a vacume down as good as any commercial pump but it was just a bit slower. It cost practically nothing.

Here is what I did: You cannot use the compressor as is because it will overheat quite quickly. I suppose it depends on freon circulation to liberate its own internal heat. I cut off the upper 1/3 of the sealed casing being carefull not get too many shavings into the innards. What shavings did go in I flushed out afterwards. What you will see is a small motor/pump unit mounted to the bottom half of the shell surrounded by a pool of oil. I sweated a male AC type fitting and shut off valve to the input side of the pump and it was ready.

When using it is necessary to keep oil in the bottom of the casing. Yes it will splash around a bit and spurt out the pump outline but I just redirected that line to squirt into the base. Had to keep an eye to make sure motor did not overheat and that that the oil did not run out. Even considered mounting a small fan on the motor shaft but never got around to that. I used it off an on for several years. I even sweated a fitting to the pump high side for pressure but it pumped out some oil too. It would achieve very high prssure. I suppose you could put some kind of oil filter on that line and use it as a compressor too.

I am not suggesting the this rig would be suitable for daily heavy duty use but it worked fine for me. I finally gave it away when I was transferred out of the country. I am planning to do this again soon. Will post results.