Evacuating A/C System
Thread Starter
Race Director
Joined: Jul 2004
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From: Scottsdale Arizona
Evacuating A/C System
Fellow CA tree huggers please stop reading here!
I have an A/C system that was completely discharged during an engine change. I've flushed the system out and changed all of the o-rings. I've converted the fittings to R134A. I've also leak tested using a commercial leak test product. The only thing that I can't do myself is to evacuate the system
My question. Assuming that the primary purpose of evacuating the system is to remove the air and moisture, is there any reason that I couldn't use a couple of (extremely cheep) cans of R134 and simply discharge the system prior to filling with oil and the final gas charge? This is much the same system that is used for charging empty propane tanks. The purpose is to reduce the partial pressure of the air.
Any thoughts?
I have an A/C system that was completely discharged during an engine change. I've flushed the system out and changed all of the o-rings. I've converted the fittings to R134A. I've also leak tested using a commercial leak test product. The only thing that I can't do myself is to evacuate the system
My question. Assuming that the primary purpose of evacuating the system is to remove the air and moisture, is there any reason that I couldn't use a couple of (extremely cheep) cans of R134 and simply discharge the system prior to filling with oil and the final gas charge? This is much the same system that is used for charging empty propane tanks. The purpose is to reduce the partial pressure of the air.
Any thoughts?
Tech Contributor
Joined: Aug 1999
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From: At my Bar drinking and wrenching in Lafayette Colorado
Purging the system in that manner won't actually remove all air from the system. It really needs to be pulled down to a vacuum for a good reliable fill. You can rent the A/C vacuum pumps and do the job right.
Tech Contributor
Joined: Aug 1999
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From: At my Bar drinking and wrenching in Lafayette Colorado
25 inches is about right, but it will vary slightly with your atmospheric pressure (density altitude). At my altitude I seldom see more than 23 inches.Whatever you pull, leave it on the pump sucking it down for 30 minutes as mb states above. Then, close off the valves and let it sit for about 15 and observe if the vacuum holds. A good tight system will hold the vacuum hard with no degredation. If you loose vacuum, start looking for leaks...
Burning Brakes
Joined: Apr 2004
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The main purpose of applying a vacuum is to lower the boiling point of water and draw the water vapor from the system. Sorry, you cannot purge the water with refrigerant. There are some inexpensive vacuum pumps that use shop air to generate the vacuum. I've not tried one, but they are low risk investment wise.
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Safety Car
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From: St. Charles IL
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You won't get hardly any dehydration at 25". If that's all the pump will pull, use the triple-sweep method. Pull the deepest vacuum you can, break the vacuum with 134A and let it sit for 30 minutes. Repeat 2 more times, then recharge with the 4th time. The refrigerant vapor will "blot up" any moisture and you will wind up with a clean and dry system.
Le Mans Master
Joined: Sep 2000
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From: Orlando Floriduh
You can buy a venturi type vacuum pump from Harbor frieght for $15 they work great but you need a big compressor. Mine pulled 28"hg very quickly with a 5 hp 60 gal compressor. I was very impressed with how good it worked. Mine was on sale for $10... That's TEN dollars. It is a little noisey though.
Thread Starter
Race Director
Joined: Jul 2004
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From: Scottsdale Arizona
Thanks Larry,
My compressor may not be up to the task, but noise bothers me very little. Probably bothers my neighbors more, but you can't please everyone.
Thanks for the tip.
My compressor may not be up to the task, but noise bothers me very little. Probably bothers my neighbors more, but you can't please everyone.
Thanks for the tip.
Le Mans Master
Joined: May 2003
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If you want to evacuate and do it in a semi enviro concious way this is how
you will need
1. a/c manifold or something with a scrader hook up and preferable a on off vavle.
2. one empty bottle of gatorade..any flavor will do in the large bottle variety.
step one. fill gatorade bottle 2/3 of way up with water.
step two. hook up schraeder(sp) valve to a/c and put other end of hose into the water.
step three. open valve. the gatorade bottle does two things...catches much of the pollutents and mineral oil. Some will still get out. It also masks the sound so your neighbors don't wonder what that loud hissing is.
step 3. Should you accept this mission Mr. Phelps, throw this computer away, it will self destruct in 10 seconds
you will need
1. a/c manifold or something with a scrader hook up and preferable a on off vavle.
2. one empty bottle of gatorade..any flavor will do in the large bottle variety.
step one. fill gatorade bottle 2/3 of way up with water.
step two. hook up schraeder(sp) valve to a/c and put other end of hose into the water.
step three. open valve. the gatorade bottle does two things...catches much of the pollutents and mineral oil. Some will still get out. It also masks the sound so your neighbors don't wonder what that loud hissing is.
step 3. Should you accept this mission Mr. Phelps, throw this computer away, it will self destruct in 10 seconds
Safety Car
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From: St. Charles IL
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Originally Posted by Larry B.
Mine pulled 28"hg very quickly with a 5 hp 60 gal compressor.
Racer
Joined: Mar 2003
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From: Mechanicsville VA
Oh, c'mon! Spend $75 to $100 and have your local automotive a/c expert evacuate and charge it! You own a Corvette, after all!
And, the triple evac is generally performed using nitrogen, certainly enviromentally-friendly stuff (we breathe a mixture containing almost 80% N2). Cheaper than R-134a, too, but then again, I have access to a vacuum pump for free...
And, the triple evac is generally performed using nitrogen, certainly enviromentally-friendly stuff (we breathe a mixture containing almost 80% N2). Cheaper than R-134a, too, but then again, I have access to a vacuum pump for free...
Thread Starter
Race Director
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From: Scottsdale Arizona
munday - The sytem is empty now and I've already done my harm by rinsing with mineral spirits and clearing the hoses with compressed, dried air.
Puresilver - It isn't so much the cost of evacuation (though I am quite stingy, i must admit). This is more along the lines of education and the ability to make repairs as is convenient to my schedule. If I would ever stick a screwdriver through a fitting while working on the weekend, it's only a matter of !) Swearing a lot, 2) Getting the replacement part that I just broke and 3) Doing the same thing that I've already done to get the sytem up and running.
I don't know if you saw the string the other day about doing wheel alignments in your garage. I must admit that my first thought was "why bother?" I've now tried it and it works shockingly well.
This idea sprung from that revelation.
Puresilver - It isn't so much the cost of evacuation (though I am quite stingy, i must admit). This is more along the lines of education and the ability to make repairs as is convenient to my schedule. If I would ever stick a screwdriver through a fitting while working on the weekend, it's only a matter of !) Swearing a lot, 2) Getting the replacement part that I just broke and 3) Doing the same thing that I've already done to get the sytem up and running.
I don't know if you saw the string the other day about doing wheel alignments in your garage. I must admit that my first thought was "why bother?" I've now tried it and it works shockingly well.
This idea sprung from that revelation.
Safety Car
Joined: Jul 2002
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From: St. Charles IL
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If you live in the Chicago area I would be happy to evacuate the system for you. If you don't have the right equipment to do these things you are beating a dead horse. You will only have problems later. I can relate to what you are saying though, about taking pride and having the educational experience and all. You could make a vacuum pump from an old refrigerator compressor. If it's reasonably healthy it should pull 28" vacuum. I don't think it would be the tool of choice for day after day use.
Puresilver, you are correct about the use of nitrogen, but for a guy to do this that doesn't have a vacuum pump, then to come up with a nitrogen cylinder and regulator as well?
Puresilver, you are correct about the use of nitrogen, but for a guy to do this that doesn't have a vacuum pump, then to come up with a nitrogen cylinder and regulator as well?
Race Director
Joined: Sep 1999
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From: Plano TX
Around here you can rent a professional vacuum pump for $15 for the weekend. Years ago I bought a robinair pump off ebay for $160. At the time I was wondering if I'd ever use it, but over the years I've lost count of the times it came in handy.
Racer
Joined: Mar 2003
Posts: 268
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From: Mechanicsville VA
Oh, I fully understand what you want to do. Being an engineer (in commercial air-conditioning...), and somewhat of a hands-on perfectionist myself (OK, some people have called me '****'), I try to do things the right way. Wasting refrigerant (even something relatively inert like R-134a) is not in my nature.
I view my 'Vette as a learning tool- I'm in the middle of completely rebuilding the posi unit and differential, among other things. I have, for sake of expediency, safety, and not being able to afford, steal, or borrow the proper tools, 'outsourced' some things like T-arms and rear wheel bearings. Know when to say when.
Someone you know must know someone who has access to a vacuum pump. Half of the battle of keeping these beasts alive is knowing who to call for advice (this forum is nice, but not everyone is within a 30-minute drive). I'd be glad to help, but the drive will take you too long, and it goes thru some deserts...
So, keep digging for your source(s) and have fun working on it.
I view my 'Vette as a learning tool- I'm in the middle of completely rebuilding the posi unit and differential, among other things. I have, for sake of expediency, safety, and not being able to afford, steal, or borrow the proper tools, 'outsourced' some things like T-arms and rear wheel bearings. Know when to say when.
Someone you know must know someone who has access to a vacuum pump. Half of the battle of keeping these beasts alive is knowing who to call for advice (this forum is nice, but not everyone is within a 30-minute drive). I'd be glad to help, but the drive will take you too long, and it goes thru some deserts...
So, keep digging for your source(s) and have fun working on it.
Thread Starter
Race Director
Joined: Jul 2004
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From: Scottsdale Arizona
I'm with you PureSilver. I've seen "type 3" personality on job evaluations before as well.
I think that I've seen enough to tell me to stop fooling around and rent a pump thought I still find the idea of the air venturi intriguing. I may even try both for the heck of it and post the results.
Surprisingly enough, i do have Nitrogen and a regulator (I teach technical SCUBA diving as well) and had thought to use this as a flush but decided that it would increase the overal pressure of the system. In the end, I'd still need to evacuate but at least the water load would be less.
I think that I've seen enough to tell me to stop fooling around and rent a pump thought I still find the idea of the air venturi intriguing. I may even try both for the heck of it and post the results.
Surprisingly enough, i do have Nitrogen and a regulator (I teach technical SCUBA diving as well) and had thought to use this as a flush but decided that it would increase the overal pressure of the system. In the end, I'd still need to evacuate but at least the water load would be less.
Safety Car
Joined: Jul 2002
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From: St. Charles IL
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A CI-6 Car Show Winner
If you have nitrogen, go ahead and use it for the triple sweep method. Another nice thing about the nitrogen is you could put maybe 100 PSIG of pressure on the system and observe for any loss of pressure (indicating a leak). Let it stay in there overnight to be sure. Nitrogen vapor pressure won't change hardly at all with changes in temperature. There really would be no need to go more then 100-150 pounds. For the triple sweep you only need maybe 5 or 10 pounds pressure.
Last edited by Big Fish; Aug 20, 2004 at 03:37 PM.