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Vacuum pumps are not really measured in PSI.. rather their ability to reach really LOW micron ranges. In residential (generally the sloppiest area... ), we try to pull down to 500 microns... that is from 760,000 microns atmospheric pressure. One can see an acceptable depth of vacuum is DEEP.

At the other end of the scale... my Appion vacuum pump will pull under 100 microns if I leave it on a system for about an hour. If I just connect it to a vacuum gauge... it will literally show 10 microns in less than a minute. That works out to 1/76,000 of atmospheric pressure...

I suspect the little pump you posted would work for hobby projects and such... be sure you keep the oil clean and give it time to do its job. Smaller capacity pumps take longer to pull a DEEP vacuum.

How much psi do you think I would get from a 1.5 CFM, 1-stage, 1/6 hp vacuum pump? I'm looking at this one http://www.mechanicstoolsupply.com/R..._p_18677.html# Another question, how long do you thing I could run a pump like that for? I didn't see any info on that.

Thanks for responding again. You guys are helping tons. I'm pretty much an idiot when it comes to this stuff.

You know, it would really just be general purpose vacuum pump. I'm trying to learn how refrigeration systems work, too. So it would be handy to have one around. But tt sounds like it would cost me nearly as much to fix this compressor than to buy one. Also, it's a 230v compressor that runs on 26.5 amps. I'm thinking this means I'll have to either upgrade a power source form the mains in my house or buy a 120/230v converter. I'm I'm wrong here please tell me. I'm probably better off going to Harbor Freight and buying one for 100 bucks. Can you suggest any other good sources for a pump?

And for the record, I don't use them anymore. They are probably more trouble than they are worth.

Originally Posted by ga-hvac-tech

One cannot draw deep enough vacuum for anything associated with AC or refrigeration.

I used to use them to do mvacs. BUT I had to leave them hooked up running overnight to get a decent vacuum.

Seen folks use compressors from refrigerators for vacuum pumps... what is said about oil above is important... check it EVERY time you use your new 'custom' vacuum pump...

Problem with doing vacuum this way is: One cannot draw deep enough vacuum for anything associated with AC or refrigeration.

For things like jewelry work (castings need a vacuum to get the air bubbles out), this can work.

I am curious, what are you planning to use this for?

Refrigeration compressors also rely on the cool returning refrigerant to cool the motor. If you use a compressor as a vacuum pump it will overheat over time. You will vaporize the oil in the crank case under a vacuum and the oil vapor will be pumped out so you would also need to make sure there is enough oil in the compressor at all times.

Me and my Dad used to make em out of compressors like that. They tend not to last very long unless you can change the oil in them.

IMO, this endeavor is most likely a waste of time. And a compressor.

Originally Posted by craig1

What is the vaccuum pump going to be used for?

good point.

While a compressor CAN pull a vacuum, it really isn't designed to do so and it won't do the same job as a proper vacuum pump will.

What is the vaccuum pump going to be used for?

Originally Posted by ammoniadog

If it has a start and a run capacitor, it "might" be possible for it to start without the start capacitor, but you will need the run capacitor. Otherwise it will over amp. I can't think of any possible way to rig up a centrifugal switch, but if you can figure it out, go right ahead and try it. I would have to believe it would be much better and easier to use the stock start components, though.

Thanks for responding. I was actually able to get the original start/run capacitors and relay switch from the air conditioner but they look very old and worn. I was thinking of just ordering a 3-Wire Mechanical Potential Relay & Start Capacitor 3.5 to 4.5 HP from Removed link to direct purchase site If I get a run capacitor and this, it should work fine, right?

Also I was thinking that I would want to vary the vacuum pressure. I've read that this compressor runs on 26.5 amps (this seems really high!!) but most of the variable controls I've found are rated at 10 amps Removed link to direct purchase site. Any ideas on how I could handle that? Or would the compressor even run on reduced amperage?

Please let me know what you think of these ideas. I'd hate to fork out a bunch of cash on this stuff only to find that it doesn't work.

If it has a start and a run capacitor, it "might" be possible for it to start without the start capacitor, but you will need the run capacitor. Otherwise it will over amp. I can't think of any possible way to rig up a centrifugal switch, but if you can figure it out, go right ahead and try it. I would have to believe it would be much better and easier to use the stock start components, though.

Repurposing Compressor into a Vacuum Pump

Hopefully, this is the right place for this post. If not, I apologize. On my property is an old cooling house that was loaded with various coolers and such (there is quite a bit of parts if anyone is interested). I pulled a Copeland CRL3-0350-PFV (4 HP, 208-230V, 47,500 BTU) compressor from one of the industrial air-conditioners hoping to re-purpose it into a vacuum pump. I believe it has a capacitor start motor. Could I start and use this without a capacitor, using just a centrifugal switch? Or would it be necessary to insert the capacitor in series with the phase winding as usual? Also could I adjust the vacuum from the compressor by adjusting voltage (would it still work)?