Vacuum pump for HVAC

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I have an oiless vacuum pump. It will pull 25" Hg. Is that enough for air conditioner line evacuation or do I need more sucking power?
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NO. You got the wrong kind of vacuum pump for airconditioning work. It is not even in the ball park for that purpose.
Stretch
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No, its not. For R410a, its not even close, and for 22, its not even marginal. What brand of micron gauge did you buy?
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This is Turtle.
User , 25'' would be just maybe fair on a 100ºF+ day and very dry day but 25" is just kind of on the short side to saying you pulled a good vacuum. you really need to get you a 29" vacuum unit to do a good job.
TURTLE
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TURTLE wrote:

Thanks. I might be able to get another vacuum pump and put them in series. I can get >29" easily that way.
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This is Turtle.
If a Vacuum punp can pull a 25" vacuum it will only pull a 25" vacuum and series them is right next to nothing but yoiu may try it. You really need a Vacuum pump made to try to gert to the 29'' magic number.
TURTLE
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TURTLE wrote:

I think I am just going to call A/C guy. This is too much trouble.
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This is Turtle.
If You get close to the 29 inches and under 400 Microns. It will mean a clean system for a long running life.
TURTLE
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You suck enough all by your lonesome!
rusty redcloud
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User Example wrote:

I use a compressor from an old refrigerator for automotive AC work. It'll pull 30" vacuum with no problem.
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LOL No, it wont.. What brand of Micron gauge are you reading this with, cause if its with your manifold, its wrong.

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I only worked on automotive AC and use the same Snap-On R134A manifold set that any other mechanic uses. The HVAC techs I've had work on my home AC unit use identical manifold sets, but with different pressure ranges. Is there a more appropriate gauge for that purpose?
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The manifold gage reads suction in inches of mercury.
An inch is 24.5 MM
A micron gage reads in 1/1000 of a milimeter, or 1/25,400 of an inch. A refrigeration guy will want to get down to 500 or fewer microns. Your manifold gage won't read that, accurately.
Do a google search on "micron gage" and see what you learn.
--

Christopher A. Young
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Uhm, where to begin.
While your gage may point to 30, a perfect vacuum is the same number as the barometric pressure for the day. Ever had a barometric pressure of 30? I didn't think so.
--

Christopher A. Young
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User Example writes:

If you vacuum-flush-repeat with refrigerant a few times it will be. Just don't tell the EPA.
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Richard J Kinch wrote:

How do you do that? I'm interested.
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Why not get a good vacuum pump fesigned for the job instead of doing slack work with the wrong machine. $30,000 fine and 5 years in prison if one of your customers turns you in for venting. Triple purge and evacuate USED to be legal, but even then you were supposed to use a DEEP vacuum pump. Your manifold gauge cannot measure a deep vacuum, they are not accurate and the resolution is too low. Get good tools and instruments. Of course if you are doing the work for yourself, maybe you deserve the results.
Stretch
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User Example writes:

Pull the best vacuum you can, repressurize with refrigerant gas. Repeat.
Sort of like rinsing a bottle you can't quite empty.
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Richard J Kinch wrote:

Gotcha. Actually, looking at my A/C manual, that's the way it says to install it. It just says run the freon out from the high to low side.
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