So you say you need a vacuum pump to evacuate your AC system for charging

xr7g428 · Sep 14, 2007

I know that I don't know exactly how these things work... I am certified in Shiner Appreciation.

When you are talking valve you are talking about the 3 way service valve. Right?

Don't these compressors use reed valves? Will the reed valve stay closed with no pressure on the high side? It seems like if the high side were open, that the reed valve would stay open and the air would move in and out throught the open reed valve. keep in mind, that this is a compressor (blow), not a pump (suck). I thought you had to have pressure on the low side to get the low side reed valve to open.

Obviously this must be different on an old refrigerator style compressor. Do they have a different type of valve set up?

greenmachine · Sep 15, 2007

Here is an article I found in an old MOTOR repair manual, 1974. This may clear up some of the debate where the idea of using the compressor came from for system evacuation. Later publications state never to use the compressor.

Evacuate System Using car engine as a pump

This procedure is recommended to be used only in an emergency. If a vacuum pump is not available, the compressor should be operated no longer than necessary to remove air from the system<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com

A vacuum pump must be used for complete moisture removal. The practice of using the car's engine to operate the compressor as a vacuum pump will prove detrimental to the compressor. No compressor manufacturer recommends this procedure.<o></o>
1. With gauges connected into system, mid-position high and low side compressor service valves (if used). Open high side gauge manifold hand valve. Operate engine at slow idle speed.<o

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2. Close high side gauge manifold hand valve when compound gauge reaches 20-25" of vacuum. <o></o>
NOTE: When using the car engine for pump-down, the compound gauge will seldom if ever drop after 25" of vacuum. Continued operation after 25" of vacuum has been reached will increase wear and cause possible damage to the compressor as it is operating<o

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>
without sufficient lubrication.<o

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3. Shut off car engine. Then check ability of system to hold a vacuum by watching the compound gauge to see that gauge does not rise at a faster rate than 1" vacuum every 4 or 5 minutes. If compound gauge rises at too rapid a rate, install a partial charge<o

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>
and leak-test the system. Then purge system and repeat above procedure. If gauge rise is satisfactory, charge<o

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system with refrigerant.<o

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>
<o

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c7xr7 · Sep 15, 2007

xr7g428 said:
keep in mind, that this is a compressor (blow), not a pump (suck).

I get what you're saying, but, it makes one wonder why all a/c systems have a what they call a "suction" line... things that make ya' go hmmmmmm?

I was an hvac techie (residential/small business, not auto) in my youth - 10 years of it and while I believe the automobile a/c compressor could be used to pull a vacuum, I wouldn't want to put that kind of stress or load on my compressor. Automobile compressors are pretty tough devices, some of the few things that cause them to fail include; Moisture in the system, dirt, failure to open service valves before operating, improper oil quality/quantity, and a few other things related to the belt and clutch. They really were not designed to pull meaningful vacuums, one of the reasons why technicians use external vacuum pumps.

For me, I would just rent or borrow a vacuum pump and keep my system clean, closed and dry. You guys do whats good for you and your situations, it may be that is all you have available.

gearhead1218 · Sep 15, 2007

Having done commercial and residential refrigeration for almost 25 years, I think I know a little bit about this subject and have decided to enter into the fray.
You CAN hook a vacuum pump to just the low side to pump down the system. It will take double or more time to properly evacuate it but you can do it. But, why would you if you have a high side port to hook to.
A lot of residential and small commercial refrigeration systems only have low side taps on them. Why? It comes down to economics. The cost of parts and the labor to install them. So most techs in the field only use the low side access to service the system, unless changing the compressor, or filter drier. Then one sometimes gets added.
Using a small refrigeration compressor is an OK substitute to buying a real vacuum pump. As long as you don't use it for larger systems (like home AC systems).

And as far as the name calling goes, come on people, we're all adults here.
Information is good. Sometimes the way It's given may be translated wrong, but it's still information, which in the end is a good thing.

Art · Sep 15, 2007

greenmachine said:
Here is an article I found in an old MOTOR repair manual, 1974. This may clear up some of the debate where the idea of using the compressor came from for system evacuation. Later publications state never to use the compressor.

Evacuate System Using car engine as a pump

This procedure is recommended to be used only in an emergency. If a vacuum pump is not available, the compressor should be operated no longer than necessary to remove air from the system1. With gauges connected into system, mid-position high and low side compressor service valves (if used). Open high side gauge manifold hand valve. Operate engine at slow idle speed.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comhttp://www.mercurycougar.net/forums/ /><o:p></o:p>[/FONT]
<FONT face=A vacuum pump must be used for complete moisture removal. The practice of using the car's engine to operate the compressor as a vacuum pump will prove detrimental to the compressor. No compressor manufacturer recommends this procedure.<o></o>
<font face=" /><o></o>
<FONT face="Times New Roman">2. Close high side gauge manifold hand valve when compound gauge reaches 20-25" of vacuum. <o></o>
<FONT face="Times New Roman">NOTE: When using the car engine for pump-down, the compound gauge will seldom if ever drop after 25" of vacuum. Continued operation after 25" of vacuum has been reached will increase wear and cause possible damage to the compressor as it is operating<o></o>
<FONT face="Times New Roman">without sufficient lubrication.<o></o>
<FONT face="Times New Roman">3. Shut off car engine. Then check ability of system to hold a vacuum by watching the compound gauge to see that gauge does not rise at a faster rate than 1" vacuum every 4 or 5 minutes. If compound gauge rises at too rapid a rate, install a partial charge<o></o>
<FONT face="Times New Roman">and leak-test the system. Then purge system and repeat above procedure. If gauge rise is satisfactory, charge<o></o>
<FONT face="Times New Roman">system with refrigerant.<o></o>
<FONT face="Times New Roman"><o></o>

Thank you for posting.

427GTE · Sep 15, 2007

Art, I have done it the way you described on my Kenworth. Three years later still blows 36 degrees out the vents. Same compresser, dryer and expansion valves. No problem. And the old fridge compresser didn't even have a snap-on sticker on it!

BigMatt · Sep 15, 2007

I wouldn't think that your AC compressor could pull that kind of vacuum. That is pretty cool.
I guess the main concern that I would have after all of this discussion is the lack of oil lubricating your AC compressor while you are running it without the oil carrying refrigerant. I have burned up compressors on cars, and it really is pretty easy to do.

Royce Peterson · Sep 15, 2007

If you close the high side valve blocking the hose the compressor high side is still open.

Just get a vacuum pump. My little Snap On ejector vacuum pump cost about $100 but there are identical looking made in China ones at Harbor Freight for something like $25. It's not worth wasting your time and freon to do it any way except the right way.

1969XR7Vert said:
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.

1969XR7Vert · Sep 15, 2007

xr7g428 said:
I know that I don't know exactly how these things work... I am certified in Shiner Appreciation.

When you are talking valve you are talking about the 3 way service valve. Right?

Don't these compressors use reed valves? Will the reed valve stay closed with no pressure on the high side? It seems like if the high side were open, that the reed valve would stay open and the air would move in and out throught the open reed valve. keep in mind, that this is a compressor (blow), not a pump (suck). I thought you had to have pressure on the low side to get the low side reed valve to open.

Obviously this must be different on an old refrigerator style compressor. Do they have a different type of valve set up?

Bill,

I am certified in shiner appreciation too!

Yes, I am talking about the (high side) 3 way service valve as a means to isolate the (car) compressor high (discharge) side from the high side line going to the expansion valve, evaporator coil, etc... The compressor high (discharge) side would be open to the air by way of a manifold set and venting what the compressor scavenges from the low side, low side lines, condensor coil, filter/drier, evaporator coil, expansion valve and high side line up to the high side 3 way valve (which would be closed) on the compressor.

The compressor valve type (internal, not 3 way) does not really come into the equation, the compressor of whatever type (car or old refrigerator) is being used as a vacuum pump by virtue of having it's high side vented to the air and it's low side connected to what's being evacuated.

Not sure what old refrigerator compressor valve configurations are, but I seem to recall that they are generally rotary compressors.

1969XR7Vert · Sep 15, 2007

gearhead1218 said:
You CAN hook a vacuum pump to just the low side to pump down the system. It will take double or more time to properly evacuate it but you can do it. But, why would you if you have a high side port to hook to.

Using a small refrigeration compressor is an OK substitute to buying a real vacuum pump. As long as you don't use it for larger systems (like home AC systems).

Interesting. I don't recall evacuating both sides (but maybe I have done this) and always have found that there is enough leakage through the system compressor and expansion valve or capillary tube (as the case may be) that the high side pulls down right along with (perhaps slightly lagging) the low side when evacuating the low side. I always thought/figured the low side was chosen because the lines, etc... are bigger and have the majority of volume to be evacuated.

Intuitively it makes good sense to open both the high and low side valves of the manifold set when evacuating, so the pump can evacuate both sides of the system most easily and not have to get to one (the high) side via the other (low) side. The notion of using the low side only comes into question when you consider using the systems compressor as a means to evacuate or if that's all you have (as you point out).

In fact the presence of only one (Schrader) port on newer, cheaper systems (again, as you point out) PROVES that the high side can be evacuated via the low side even is that is not the ideal way to do it. Thanks for the info and experience and for "entering the fray"!

Bob

1969XR7Vert · Sep 15, 2007

greenmachine said:
Here is an article I found in an old MOTOR repair manual, 1974. This may clear up some of the debate where the idea of using the compressor came from for system evacuation. Later publications state never to use the compressor.

Excellent and thanks!

Interesting that they suggest both service valves at mid position rather than my suggested method of high side valve closed and low side valve open. Maybe they were concerned with how to close the high side Schrader (bad for a compressor high side to be blocked) while simultaneously shutting off the car. This would have to be done in order to avoid losing the vacuum that was pulled.

By the way, and while we are being controversial, did you know that on a house AC condensor/compressor if you need to change the condensor/compressor (the compressor has to work though), you can use the compressor to push most/all of the freon into the condensor coil and trap it there? It has to do with the service valve location/configuration, IIRC the high side service valve is after the condensor coil which enables this operation. You close the high side valve while the system is running and watch the low side pressure. When it gets into the low single digits, you simultaneously close the low side service valve and shut the system off. You now have most/all of the system freon trapped in the condensor coil and can open the lines to the house without venting refrigerant, do the work, close the system, evacuate, then reintroduce the freon which is trapped in the condensor coils.

Another interesting fact is that all (to my knowledge) newer home AC condensor/compressors come with the refrigerant in them, stored in the condensor coil. When installing them the house part of the system is evacuated and then the condensor lines cracked open. You only need additional refrigerant if the lines are more than 25? ft. long.

1969XR7Vert · Sep 15, 2007

Royce Peterson said:
If you close the high side valve blocking the hose the compressor high side is still open.

Just get a vacuum pump. My little Snap On ejector vacuum pump cost about $100 but there are identical looking made in China ones at Harbor Freight for something like $25. It's not worth wasting your time and freon to do it any way except the right way.

Yup, compressor high side open, that is how you get the air/moisture out of what is behind the compressor high side (the whole rest of the system).

I agree about and use a vacuum pump. We have simply been discussing an (albeit not as good) alternative. Even if not a good idea, it is interesting from a educational point of view and exercises the ole synapses a little, don't you think?

I also agree that to waste and/or vent R-12 is both costly and bad for the environment.

Good tip on HF and their unit(s). Not even $25, $15.99!:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=3952

The R-134A unit is even less at $9.99:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92475

They state only 4.2 CFM which is lower than the 5-7 John (Gearhead) suggests, but they also state 28.3" of vacuum which I gather is pretty good vacuum for this application.

So there you go, cheap at HF and you really cannot argue with a cheap, good vacuum source. Still in all I have enjoyed (for the most part) the discussion.

1969XR7Vert · Sep 15, 2007

BigMatt said:
I wouldn't think that your AC compressor could pull that kind of vacuum. That is pretty cool.
I guess the main concern that I would have after all of this discussion is the lack of oil lubricating your AC compressor while you are running it without the oil carrying refrigerant. I have burned up compressors on cars, and it really is pretty easy to do.

Most of the refrigerant oil resides in the compressor to my knowledge.

BigMatt · Sep 15, 2007

My dad has an invention that may be of some help here. It is the Spooter II from ICOR International. It is a hand powered reclaimation pump and would be great for these situations.

Here is the product information page: http://www.icorinternational.com/index.php?main_page=document_general_info&cPath=5&products_id=9

I am not sure of his distributors, but you could call and ask.

Here is one on EBAY http://cgi.ebay.com/HOT-SHOT-SPOOTER-II_W0QQitemZ150121130495QQihZ005QQcategoryZ109488QQrdZ1QQssPageNameZWD1VQQcmdZViewItem

They work great and can pull a hell of a vacuum. You would just pull as much of a vacuum as you can, let the moisture boil off and then give it a few more pumps, rinse and repeat until you are satisfied that the system is evacuated.

1969XR7Vert · Sep 15, 2007

BigMatt said:
My dad has an invention that may be of some help here. It is the Spooter II from ICOR International. It is a hand powered reclaimation pump and would be great for these situations.

How cool is that? A bicycle pump type device that let's you handle a lot of otherwise impossible situations for the average car guy. Pretty neat.

BigMatt · Sep 15, 2007

Yeah, That was my dad's first invention when he was a refrigeration service man. The EPA had just started phasing out R-12 and the Spooter II was really the first thing out there that made it possible to reclaim all the refrigerant in an AC system without buying a bull blown reclaimation pump.

By the way, it was named ater our old dog, that's why it is the Spooter II.

Royce Peterson · Sep 16, 2007

Wow, they must have lowered the price! I bought four of them at Harbor Freight about 12 years ago for $22 each to use on a large structural graphite composite repair. I remember that after giving the cashier $100 I had just enough change to get dinner at Burger King. They worked every bit as well as my Snap On unit.

It does not cost more to do the job right. It costs more to do the job wrong.

1969XR7Vert said:
Yup, compressor high side open, that is how you get the air/moisture out of what is behind the compressor high side (the whole rest of the system).

I agree about and use a vacuum pump. We have simply been discussing an (albeit not as good) alternative. Even if not a good idea, it is interesting from a educational point of view and exercises the ole synapses a little, don't you think?

I also agree that to waste and/or vent R-12 is both costly and bad for the environment.

Good tip on HF and their unit(s). Not even $25, $15.99!:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=3952

The R-134A unit is even less at $9.99:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=92475

They state only 4.2 CFM which is lower than the 5-7 John (Gearhead) suggests, but they also state 28.3" of vacuum which I gather is pretty good vacuum for this application.

So there you go, cheap at HF and you really cannot argue with a cheap, good vacuum source. Still in all I have enjoyed (for the most part) the discussion.

70_cougar · Sep 16, 2007

Air powered venturi vacuum pumps

This article is from here http://www.aircondition.com/tech/questions/38/

Ambient temperature is important when you try to use one of them.

If we wish to lower the boiling point of liquid, we simply remove the pressure that's on top of that liquid. That's how we boil water out of an air conditioning system. We use a vacuum pump to bring the system to a level of near perfect vacuum so the water will boil off and be carried away as a vapor. It's important to note that ambient temperature has much to do with the point at which liquids will boil under vacuum. The greater the temperature, the fewer microns of vacuum will be required to start the boiling process. If you've been keeping note, you know that non condensables (air) and moisture are two things you definately don't want in your a/c system.
The chart below shows how temperature plays a role in the level of vacuum needed to boil water.
<table style="page-break-before: always;" border="1" bordercolor="#000080" cellpadding="0" cellspacing="0" width="534"> <colgroup> <col width="273"> <col width="259"> </colgroup><tbody> <tr valign="top"> <td sdnum="1033;1033;@" bgcolor="#0099ff" width="273">

Inches of Mercury

</td> <td sdnum="1033;1033;@" bgcolor="#0099ff" width="259">

Boiling Point of Water °F

</td></tr> <tr valign="top"> <td sdnum="1033;1033;@" bgcolor="#99ccff" width="273">

26.45