How good of a vacuum do you need?

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Maverick9D@gmail.com
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How good of a vacuum do you need?

Post by Maverick9D@gmail.com »

Been working on restoring my '88 Mustang and adding AC back in using R12. All new NOS Ford lines, and rebuilt the compressor.

Initially I was having trouble pulling a deep vaccum and was having it stall out around 5000 microns. I abandoned the manifold guage and used an Apion VCRT, pulled the core and pulled a vac direct. This setup really works well as it holds both vacuum and pressure for days.

This seemed to help, but I wasn't I wasn't making significant progress, so i decided to introduce some nitrogen into the system. I used the opportunity to leak check as well (no leaks found, pressure would hold steady for days). Each time i filled with N2 and pulled a vacuum i was able to pull a deeper vacuum, quicker. I repeated a couple more times after that and each time was able to get deeper vacuum in a much quicker time.

I'm at the point where I am sub-200 microns, and it will pull down to this pretty quick. Stalls out around 170-180 microns. The issue that makes me think my vacuum is not quite where it needs to be is that when i close the ball valve to isolate the system it creeps up to around 1000-1200 microns and settles out there. it takes several hours to do this, so it will pass a 10 min decay easily.

Do i keep doing what I am doing with the N2 purge/vacuum, or is this good enough? I'd feel better if it stopped around 500 microns (or better) once i shut the vacuum off. I do have the luxury of time here considering it's Jan and the car is not going anywhere for a while

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Last edited by Maverick9D@gmail.com on Wed Jan 26, 2022 1:39 pm, edited 1 time in total.
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Tim
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Re: How good of a vacuum do you need?

Post by Tim »

I'd say you're fine.
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DetroitAC
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Re: How good of a vacuum do you need?

Post by DetroitAC »

That's a good vacuum, can't usually get lower because of old automotive hoses.
Maverick9D@gmail.com
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Re: How good of a vacuum do you need?

Post by Maverick9D@gmail.com »

Thanks guys.

I did it one more time. Got down to 165ish microns and after an hour or so it leveled off around 500-600 microns. I think I'm good.

Looking forward to having functional A/C on the car for the first time in the 25 years i've owned it.
tbirdtbird
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Re: How good of a vacuum do you need?

Post by tbirdtbird »

You are way better than most
In essence you are doing a triple evac, which is the best way to go.

Whatever you do, don't leave it in a vacuum, get at least a partial charge of refrigerant in there
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