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Discussion Starter #1
I PM'ed Xrundan with this, he shouted out asking to borrow a vacuum pump. Thought others might like to know. Forgive me if this is common knowledge, posting this for anyone who didn't know. Anyway:

Here's what I have used over the years, it is pretty much what a vacuum pump is made up of, and can usually be found for free. BTW: Please do not vent R-12 to the atmosphere (which is illegal and global warming is bad enough already), recover it or have it recovered for you (how do you recover it? With a vacuum pump and a suitable tank). Find an old refrigerator with a good compressor and remove it. Put the correct fitting on the suction side (larger of the two hoses) and leave the discharge side open. You now have a vacuum pump, usually for free.

Regards,

Bob
 

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I did not know that...brilliant. I use the compressed air cheapo version which doesn't generate ideal vacuum at this altitude. I'm in the process of doing the Sanden and R134 conversion on mine. Just in time for winter!
 

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You can evacuate most of the system by simply opening up the high pressure side, starting the motor, and allowing the cars compressor to pull down the system.
 

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If you want to do this once and do it right you should hook up a vacuum pump and let it sit overnight. This will remove all traces of moisture. The compressed air powered vacuum pumps in fact are excellent and do a wonderful job. Be sure to check and fill the compressor oil level before you do anything.

After pulling a vacuum you should shut the valves and turn off the vacuum pump. Let it sit 3 - 4 hours. If it holds vacuum this long then you know the system will hold freon. If not then you need to fix the leaks before proceeding.

RE: Arts idea..... You cannot adequately suck it down using the car's compressor. It will only put a suction on the low side, and all the moisture ends up on the high side. So this is ridiculous and a waste of time.
 

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RE: Arts idea..... You cannot adequately suck it down using the car's compressor. It will only put a suction on the low side, and all the moisture ends up on the high side. So this is ridiculous and a waste of time.
I didn't say it was the correct way to evacuate the AC system, I said it would evacuate MOST of the system.
By closing the low side Schrader valve, opening the high side and running the compressor you evacuate BOTH the high side and low side.

Please let your ego accept the fact that others on this board have some useful tech to share.:)
 

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It's not an ego issue. What you are recommending won't work. If the high side is open it is not being evauated. This will leave a significant amount of air in the system. This will also make it impossible to fill the system with a full charge of freon, and the remaining air and moisture will contaminate the dryer and cause icing, compressor damage and reduced flow. Temperature and pressure differential will be significantly reduced and the cooling will be less than acceptable.

Other than that it is just fine :uhoh:


I didn't say it was the correct way to evacuate the AC system, I said it would evacuate MOST of the system.
By closing the low side Schrader valve, opening the high side and running the compressor you evacuate BOTH the high side and low side.

Please let your ego accept the fact that others on this board have some useful tech to share.:)
 

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Discussion Starter #7 (Edited)
RE: Arts idea..... You cannot adequately suck it down using the car's compressor. It will only put a suction on the low side, and all the moisture ends up on the high side. So this is ridiculous and a waste of time.
Actually, since the low side is connected to the high side via the expansion valve (and by whatever they call the transition on systems with no valve), I believe the high side would be evacuated as well *IF* you can close off the high side line and allow the compressor output to vent. The compressor valves allow this very configuration if you close the high side compressor valve (sealing off the high side line) and open the compressor high side schrader valve (usually using a gauge set). Nearly all of the system would be evacuated including the high side line up to the compressor valve, fairly complete I would say.

Still, drawing down overnight and then looking for vacuum to be held is the only way to go to make sure the system is capable of holding a charge. You can do the same thing with Arts method but I would not let the car run overnight!
 

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Ridiculous and a waste of time

A "quickie" method that was taught to me by my auto shop teacher in high school. I have done this on discharged systems, replaced the part, then let the compressor pull the system down.
I don't recommend this, but I have done it in the past before I had a vacuum pump.

The orifice vacuum pump Royce speaks about works very well, I have one. Leaving it running overnight would be a little "ridiculous" to me because they use a LOT of air. A small air compressor would probably run constantly to keep up with it.

I've seen homemade vacuum pumps made from large refrigeration compressors that work very well.
 

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Discussion Starter #10
You hear that?

It's silence. :argue: :smooch:
 

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You guys are going to have fun with this...
Compressors are designed to blow, not to suck...

In general, compressors are inefficient pumps. They are not designed to lift a column of water (pull a vacuum), they are designed to raise a column of water (compress). The difference (among others) is in the way the valves are timed. Any one with a water well can tell you that lifting the column of water up the well shaft (vacuum) is a lot harder than pumping it up to the house (Compression).
 

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I use a 60 gallon tank / 6 HP two phase compressor. It runs for a minute or so to fill the tank then shuts off for 8-10 minutes when using the Snap On ejector vacuum pump.

You can't get below maybe 5 - 6 inches of mercury using the factory compressor on the low side. That's not low enough to boil water out. Meanwhile the high side has to be open to pull vacuum. So it ends up with lots of air and water in it. Utter waste of time. My little Snap On ejector pump pulls close to 28" (pegs my freon guages) sitting overnight. If you can't do it right take it to somebody who can. Freon is too expensive to waste.
 

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Discussion Starter #15
You can't get below maybe 5 - 6 inches of mercury using the factory compressor on the low side. That's not low enough to boil water out.
This I do not know about this so I won't comment.

Meanwhile the high side has to be open to pull vacuum. So it ends up with lots of air and water in it. Utter waste of time.
Is the high side open if you do as I suggest (close high side valve)? I don't think so. The discharge port of the compressor is open (this would be a small volume of space) but the high side line is closed and will be drawn down by the low side.

So the cars compressor abilities aside, what ends up with "lots of air and water in it"?

The only thing that appears to me as an utter waste of time here is trying to logically work through or have a productive discussion about anything with which you do not agree.
 

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Royce is 100% correct. As he stated it's not ego, but actually fact.

But, if you have access to a GOOD refrigeration vacuum pump (5 to 7 CFM or more) a system as small as an auto AC will be pumped down sufficiently in an hour or two. As long as you have a new filter drier installed it will catch any errant moisture left in the system.
An AC system that has been open for an extended time though might benefit from an extended overnight vacuum job.
 

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OK so how much formal air conditioning training do you have? I only have an 8 hour course under my belt so I am by no means an expert on the subject. But the physics involved are simple to understand. Using country bumpkin tricks won't change physics.

There can only be vacuum on the low side of a compressor if the compressor is functioning. Meanwhile the high side will always be a positive pressure value. So moisture and air will not be removed from the high side at all, in fact any moisture from the low side will be deposited in the high side and will stay there. This is simple physics if you understand how a compressor works. It is not an opinion.

This I do not know about this so I won't comment.



Is the high side open if you do as I suggest (close high side valve)? I don't think so. The discharge port of the compressor is open (this would be a small volume of space) but the high side line is closed and will be drawn down by the low side.

So the cars compressor abilities aside, what ends up with "lots of air and water in it"?

The only thing that appears to me as an utter waste of time here is trying to logically work through or have a productive discussion about anything with which you do not agree.
 

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It's OK to disagree, I have no problem with another opinion, but to use words like "idiot", "ridiculous", "waste of time", "country bumpkin" gets personal and causes me to loose respect for you Royce.

And I'm not the only one on this forum that feel this way.

I think you need to back away and think about what you type.
 

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Discussion Starter #19 (Edited)
OK so how much formal air conditioning training do you have? I only have an 8 hour course under my belt so I am by no means an expert on the subject. But the physics involved are simple to understand. Using country bumpkin tricks won't change physics.

There can only be vacuum on the low side of a compressor if the compressor is functioning. Meanwhile the high side will always be a positive pressure value. So moisture and air will not be removed from the high side at all, in fact any moisture from the low side will be deposited in the high side and will stay there. This is simple physics if you understand how a compressor works. It is not an opinion.
Actually (and thanks for asking), I am ASE (formerly NIASE) certified in AC as well as 6 or 7 other areas. Oh, and I am also certified in CFC-12 refrigerant recycling and service procedures (required to buy R-12 after a certain date and mandated to help protect the environment).

The air/moisture and whatever else will most certainly be removed from BOTH sides when you evacuate from the low side only. Otherwise you would have to evacuate both sides before charging and this most certainly is not what is done regardless of the method of evacuation.

The compressor does not even come into the equation since it is not operating (let's leave it non-operating and not the method of evacuation for the purposes of this discussion). The evacuation takes place through the system lines, not through the compressor, it's valves, etc...

I think you will agree that the vacuum pump draws down the entire system (and from the low side only), not just one side. If you think otherwise let's just end the discussion here and agree to disagree because this is a basic fact of how evacuation of a system via the low side works in practice.
 

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Discussion Starter #20
There can only be vacuum on the low side of a compressor if the compressor is functioning. Meanwhile the high side will always be a positive pressure value.
Wrong. Not if the high side (of the compressor) is open (and the high side line closed). The valve man, the valve. It isolates the high side line from the compressor high side when closed. And under these circumstances the high side (lines) are evacuated via the low side. Think about it.
 
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