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hansh
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PostPosted: Thu Jun 06, 2013 8:30 am    Post subject: A/C vacuum Reply with quote

I really don't want to further gum-up the Red Tek thread with A/C questions. I've found threads related to this question but I haven't found a good answer yet.

I've done all of the cleaning/o-ring/oil/new part prep on my ac system and now I need to vacuum the system. I'm trying to figure out the least expensive method. I'm staying in Lewiston, ID for a while and I don't have the store resources that I'm familiar with. Autozone doesn't have a rental pump nor do any of the equipment rental companies.

I can get a pump and gauges delivered from HF for just under $140. I know that I'll need the gauges but would it be cheaper to have a shop pull vacuum and check for leaks?

Hopefully I'm understanding the process correctly.
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bowtiebug
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PostPosted: Thu Jun 06, 2013 8:36 am    Post subject: Reply with quote

if you have a compressor these work great for pulling a vacuum

http://www.harborfreight.com/air-vacuum-pump-with-r134a-and-r12-connectors-96677.html


Gauges

http://www.harborfreight.com/a-c-manifold-gauge-set-92649.html
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r39o
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PostPosted: Thu Jun 06, 2013 8:38 am    Post subject: Reply with quote

How about letting a shop do it?

If you need to do it again, buy the tools.
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hansh
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PostPosted: Thu Jun 06, 2013 8:42 am    Post subject: Reply with quote

Those are the gauges I was looking at.

Re the pump. I thought I'd read that the Venturi style didn't work well. Here's my main concern: I have a small (2 gallon compressor) and I don't think it'd work. I'm staying with someone wth a larger compressor (still only like ~15 gallons / 100psi) and it is in the garage right against the interior wall. I don't want to burn up any compressors or cause a continuous racket.

That said, I don't know enough about the Venturi pumps to know if those things are realistic concerns.
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furrylittleotter
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PostPosted: Thu Jun 06, 2013 8:44 am    Post subject: Reply with quote

r39o wrote:
How about letting a shop do it?

If you need to do it again, buy the tools.


Ditto. You may want to have the system purged and pressure tested with nitrogen first.

I would not be surprised if you can't pull vacuum on it at all. Seals react different to vacuum as opposed to pressure and you might just have to pressurize from atmosphere. Not ideal but many people do it and their system is working.
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bowtiebug
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PostPosted: Thu Jun 06, 2013 8:55 am    Post subject: Reply with quote

ive been a mechanic for 30 yrs and have used this style for side jobs at home for several yrs and never an issue , thy only require like 4 cfm @ 80-90psi and they need to run that long 20 - 30 min
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tencentlife
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PostPosted: Thu Jun 06, 2013 5:26 pm    Post subject: Reply with quote

bowtiebug wrote:
if you have a compressor these work great for pulling a vacuum

http://www.harborfreight.com/air-vacuum-pump-with-r134a-and-r12-connectors-96677.html




I have one. Doesn't do the job. Only pulls down to about 10"Hg.,my compressor's plenty big. You want to get it down to 30" to draw all the moisture out. A real pump is real money, I ended up getting one, hardly ever gets used. If you're not making a business of AC service just go to a shop and have it drawn down.
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morymob
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PostPosted: Fri Jun 07, 2013 4:58 am    Post subject: Reply with quote

Way back when(?) after night AC course 4 my own info/use, teach showed how to make own, very cheap, vac pump. Know of an old frig, 25qt+ dehumidifier that still works and to be junked?? Remove compressor and i soldered on a connector for guages/hose to attch to suction side, pwr cord and handle of your choice. On my 3rd since the mid '70's and works fine, compressor size determines time to 'pull down' but left on long as needed, in no hurry. Were some new ones ready made up in the past, don't know if still 4 sale.
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Rodknock
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PostPosted: Fri Jun 07, 2013 4:59 am    Post subject: Reply with quote

I just got done with my a/c rehab and I used the HF venturi-style gizmo along with my 5.5 scfm compressor. It pulled the vacuum down far enough to pin both high and low side gauges to the stops. I ran it for 3 hours first, and I put a small fan directed toward my air compressor head to keep it cool. I let it sit overnight to check leaks (none). Then I drained the moisture out of my compressor's tank and ran it again for 2 hours. I kept the Venturi-style gizmo hanging down low below the van's engine to keep moisture out. The result is my a/c works fantastic. As good or better than it did before my a/c compressor motor died and caused this whole thing in the first place.

Note that while you are pulling a vacuum you will hear the venturi-style gizmo spit once in a while. I think this is moisture coming out of the system. Just keep running it until the spitting stops, probably 4-5 hours at least assuming you flushed the a/c system with air brake drier solution. It takes a lot longer than you expect. If you are patient the HF gizmo works fine IMHO.
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hansh
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PostPosted: Sat Jun 08, 2013 10:36 am    Post subject: Reply with quote

This is a tough call between buying a pump or paying a shop. Beside other concerns, I won't go the Venturi route as I'd be using someone else's smallish compressor. It would cost a lot more for a replacement compressor and Venturi pump than a buying a real vacuum pump or paying for service.

Paying a shop for them to use their pro tools makes sense but, since this'll be a DIY Red Tek conversion, won't I lose vacuum pressure when I need to attach my own quick connects and hoses to the Schraeder valves for charging the system?
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Rodknock
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PostPosted: Sat Jun 08, 2013 1:38 pm    Post subject: Reply with quote

Not really much at all. You'll lose a tiny bit of vacuum when quick connects are connected and disconnected. Just have the shop leave the vacuum on it.
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McVanagon
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PostPosted: Sun Jun 09, 2013 6:27 am    Post subject: Reply with quote

tencentlife wrote:
bowtiebug wrote:
if you have a compressor these work great for pulling a vacuum

http://www.harborfreight.com/air-vacuum-pump-with-r134a-and-r12-connectors-96677.html

I have one. Doesn't do the job. Only pulls down to about 10"Hg.,my compressor's plenty big. You want to get it down to 30" to draw all the moisture out. A real pump is real money, I ended up getting one, hardly ever gets used. If you're not making a business of AC service just go to a shop and have it drawn down.

Yup... You'll never pull down enough vacuum with that thing.

I struggled with one for a few years, then grew tired of wasting refrigerant to get mediocre results. Not wanting anyone to find the discarded pump and try to use it, I destroyed it.

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PostPosted: Sun Jun 09, 2013 6:31 am    Post subject: Reply with quote

r39o wrote:
How about letting a shop do it?

If you need to do it again, buy the tools.


Because by and large shops are staffed with incompetent "mechanics" who often eff something up while "fixing" your ride!
Not to mention the time, aggravation and grief of arranging rides to drop off the vehicle.

Do it yourself if you've got the ability. Tools purchased for a repair job is money in the bank for future money saving repairs!

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