I just bought a used refrigerator compressor from the local junk yard. It tested it with my MightVac and it pulls 24 in. hg. I suppose it will pull more vacuum when I put the proper fittings on it. Professional air conditioning vacuum pumps in my area will pull no more than 26 in. hg. since I live at 2000 ft. about sea level. I am not worried that it will not pull 26 in. hg.

The high side tube dips oil. I have only lost a tablespoon of oil. Should I plug the high side or add oil every so often?

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Solder a 1/4" inverted flare on the suction side. Get an adapter for the acme thread used on your 134 manifold set. That way you will be able to use it for an R12 auto a/c, the house unit or whatever, but still be able to use it on a 134 syste. If you want to get fancy, weld or bolt together a frame for it.

Since it has been running in a closed system, it will probably puke some oil for a little while. I don't think that you'll need to worry about replenishing it.

If I had it to do over with my home built from many years ago, I would have kept the suction AND pressure side capped when not in use. The suction side should be no problem, store it with the acme thread 134 adapter and find a cap from an old 134 tank to cap it off. For the high side, get creative, even if it is nothing more than a piece of rubber tubing with a bolt stuck in it, slipped over the output tubing.

Don't get the bright idea to solder another 1/4" inverted flare on the high side, you might forget and hook it to your gauges, you wouldn't want the unfiltered whatever to get in your manifold set and ultimately into the system you are working on.

Do all this and you will have a pump that will serve you the rest of your life.

Good luck,

Larry, You used the words " acme threads" twice in that last post... is that really what you were thinking about ?... Did you mean metric or something ? That would be a very unusual place to place an Acme thread.... but I will look at mine up front the first time I get out...

without my glasses it appears to be 16 tpi....and while they do look rounded... they are not flat and wide enough to be Acme...

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I am a little skeptical of the elements mentioned (or lack of) in this project...
I have used a regular vacuum ( the old style) and it had a hole which allowed water to drip out of it...
A refrigerator is closed system with the oil for the upper end of the compressor being circulated through the system in order to get it back to the top... ( I think)....
If you don't put some type of replaceable dessicant container prior to the compressor then you are going to have water in the oil and no oil being replenished to the working part of the compressor...
This may work fine if you shoot some oil into the suction end before you start each job... just like you would do an air tool....
But I still worry about the water being drawn into the compressor...

You need a vacuum of 29.97 inches of mercury at SEA LEVEL to be effective at removing moisture from a system . . . you lose 1 inch of vacuum for every 1000 ft. elevation . . . you need a Temp-rite to collect and return the oil back to the compressor . . .

The Acme thread fitting I am talking about is the flat looking threads that are on the hose on your 134 manifold gauges that connects to the vacuum pump or the 134 source. You simply put the adapter on the 1/4" inverted flare and leave it there with a cap while in storage. When using the pump, take off the cap for servicing a 134 system or take off the adapter for servicing a 12 system.

As far as the oil goes, you are now no longer using this compressor in a sealed system. A little oil will blow out, but plenty of oil will settle in the bottom and be there to keep the compressor lubed. Mine would still be working had I not left the intake out output open while setting in my very damp shop. It will work great with the oil that's in it.

The beauty of these things is that if you run it for a long time it will boil the moisture out of the oil, it will also do a better evacuation job. I like to pump down overnight if possible. Any moisture left in the system combines with the refrigerant to make an acid. This is not a good thing.

Have a great day,

Larry , the picture above IS of my 134 gauge fittings...all three are the same... the thread guage is on the center one.....

Are you meaning 'Acme" in the sense, like Wiley Coyote , of something being Generic ? Or are you really thinking about 'acme' threads like are used on the lead screw on a lathe? Which have the thread flat on top and about twice as wide as a normal thread ? I really can not figure out what you are talking about... Once the 134 change over fitting is installed.... then we are dealing with a quick disconnect fitting right ? ... but what it was screwed onto was a regular Schraeder valve fitting... right?.. so where is there a place for ' acme ' ?

OK, I went and looked at one of our late model cars...Here is what happend to Larry....

The fitting for 134a are Quick Disconnect.... just like your air compressor line fitting... spring loaded and CLIP on ....

However, the little protective covers on the 134a fittings have a secret hidden nipple inside them... and while the appear to screw onto the quick connect fitting LIP... they do not.. they screw onto the fitting on the inside of the 134a fittings.... thus giving the impression that the outer lip is a THREAD... which it is not... it is just the catch lip of the quick connect fitting.....so there are NO acme threads anywhere associated with AC stuff on your car....

Okay, I should NOT have used the word "ACME." I used that word because of the flat edge on the threads "looks sort of like" acme threads.

I was saying to put the adapter onto the 1/4" inverted flare fitting that is soldered to the 1/4" suction line on the compressor.

You then screw an adapter that is 1/4" inverted flare (R12 type fitting) on one end and male 134 service threads like you showed in your picture.

This is where you will connect the center hose from your manifold gauges when evacuating. If you are using 12 gauges, then screw off the adapter and connect your center hose directly to the 1/4" inverted flare (R12 type fitting.)

If you buy a 30 pound cannister of 134 the "acme thread looking fitting" is the fitting that is on the cannister. It is there to connect a 134 service line to. That cannister comes with a little cap that threads onto that fitting. You will not find that cap or fitting anywhere on the car. The car has the quick connect fittings for service.

Find one of the caps like goes on the cannister (I got mine when I emptied a 134 cannister) and screw it onto the adapter while the pump is not in use.

I realize that I am not very articulate, so if this does not describe what I am trying to say, then I don't know how else to get across my point.

Just call me dumb and do the best you can.

Have a great day,

I just did not want Mercedes Man to walk into a parts store and ask them for an " adapter for the acme thread used on your 134 manifold set. " And them look at him like he was crazy , when we should be able to talk/reason it out here.... I have made too many double trips to parts houses because I was not prepared the first time.... you never know how far away or how hard it is for him to get to his parts house...
Mercedes Man ,,, ask for " the quick connect adapter used on your 134 maniforld set." and you should be in good shape...
Larry, they look very much like Acme threads... I had to put my finger on the back side of them and press to make sure that they did not 'screw' but stayed parrallel...of course the also look like your air hose nipple....

Thanks every one for their input.

I did spend some time looking for the "ACME" thread. My air conditioning book says that R-134a takes a 1/2-16 acme thread. Even the cap that I have on my R-134a valve says 1/2 acme. No one sells those acme fittings.

By the way, the R134a hoses are attached to the manifold with 1/8 inch NPT.

I talked to a guy at a residential air conditioning shop, and he said it is impossible to buy the 1/2 acme fittings, so he showed me what he did. He has a real vacuum pump. He took the top a of R-134a can and epoxied a copper tube and fittings to it.

I took his idea one step futher. I do not plan to do R-12 work. I took the R-134a can and soldered it to the copper tube of the refrigerator compressor. My valve is screwed into the can, and it will connect to the service line of the gauges. I need to get a hold of R-134a gauges to do my final test.

If I run the compressor with no vacuum load, oil will come out of the discharge line. When I put the compressor under a vacuum load, maybe a drop of oil will come out of the high side. So the lesson is never run the compressor without a load.

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Here is a picture of a R-134a can cap.

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Automobile systems aren't hermetically sealed so I doubt if you could ever pull 29 inches of vacuum and if you could, it wouldn't stay that way for too long. And, I've never been able to achieve anything like that kind of vacuum when doing service on a car A/C.

While it's certainly a good idea to get all the contaminants out of a refrigeration system, a little moisture won't hurt a 134a or 12 system in a car. Any residual moisture left after 30 min or so on a correctly operating vacuum pump should be trapped in the dessicant that's in the dryer/accumulator.

Hermetically sealed refrigerator/freezer systems are another matter entirely. All moisture MUST be removed or it will freeze in the capillary tube (or expansion valve), cause a restriction in the system and limit or stop the refrigeration cycle until the restriction thaws out.

Automobile refrigeration systems should not have any below- freezing temperatures at the evaporator or their throttling devices so moisture-related freeze-up restrictions shouldn't be an issue.

Regards all,
R Leo

__________________
Never a dull moment at Berry Hill Farm.

Here is what I think I have figured out..
THe 134a can has an acme thread.
The fitting for piercing the top of the 134a can has an acme to fit.
What your 134a guages fit to , however , is the 16 pitch unifified coarse thead on the outside of the piercing manifold.
Your 134a manifold will not be dealing with any acme threads on any of its hoses... thus the "holder" back side of the 134a manifold and guages are the 'quick connect' on the outside (two different sizes) and the 16 pitch on the center (yellow usually)...
I do not think any NPT (National Pipe Threads) are used on any of these things we are talking about because the threads are not used for doing the sealing... all have either tapered ends or gaskets.... which would work against those types of sealing...

SOOOooo.... this REALLY IS an ACME thread. I guess I'm not so dumb after all. 1/2-16 Acme thread, that's what the man said.

As far as there being no such adapter, I know that is not true because I have one screwed onto the 1/4" inverted flare on my vacuum pump. The fitting is female 1/4" inverted flare and male 1/2-16 acme thread with a tapered end for sealing. I got it at the automotive a/c store in Dallas that I frequent. The name of the outfit is McClain's Auto Air. They are an EXCELLENT source of auto air supplies, equipment and assistance.

It sounds like for your purposes the fitting you have on your pump will get the job done, but had you put on the 1/4" inverted flare, then you would be able to use it for R22 systems as well, even if you don't need it for R12 automotive work.

The main thing is that you are now set up for business.

Good job,