Evacuation Procedure

Information on some common auto air conditioning topics.
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JohnHere
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Evacuation Procedure

Post by JohnHere »

"Your Mileage Might Vary," as the expression goes, but I normally try to evacuate a system for a minimum of one hour.

Special circumstances can and do present themselves, though. For example, if a vehicle with an A/C problem comes along and the owner needs it back in about two hours, that stipulation will certainly affect how much evacuation time it gets.

If I'm working on one of my own vehicles that I'm not in a hurry to finish, I'll evacuate for four or five hours and maybe even overnight depending on what time I start working on it. If I'm getting ready to hook-up the vacuum pump at, say, 11:00 p.m., I'll do so, turn in, and allow the pump to run overnight until 6:00 or 7:00 the next morning.

On the other hand, if I start evacuating at 4:00 p.m., I might keep the vacuum pump going until around 7:00 p.m., verify that the vacuum holds, proceed to charge it, and complete the job with enough time left to have a later-than-usual dinner, relax, and then call it a day.

If I know that a system is unusually "wet" for whatever reason or that it has been open for a long time, I'll go for an overnight evacuation, if possible.

I, too, use a micron gauge to supplement the low-side gauge on my Manifold Gauge Set. And I change the oil in my vacuum pump after every second evacuation.
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70monte
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Re: Evacuation Procedure

Post by 70monte »

JohnHere wrote: Sat Aug 13, 2022 6:10 pm "Your Mileage Might Vary," as the expression goes, but I normally try to evacuate a system for a minimum of one hour.

Special circumstances can and do present themselves, though. For example, if a vehicle with an A/C problem comes along and the owner needs it back in about two hours, that stipulation will certainly affect how much evacuation time it gets.

If I'm working on one of my own vehicles that I'm not in a hurry to finish, I'll evacuate for four or five hours and maybe even overnight depending on what time I start working on it. If I'm getting ready to hook-up the vacuum pump at, say, 11:00 p.m., I'll do so, turn in, and allow the pump to run overnight until 6:00 or 7:00 the next morning.

On the other hand, if I start evacuating at 4:00 p.m., I might keep the vacuum pump going until around 7:00 p.m., verify that the vacuum holds, proceed to charge it, and complete the job with enough time left to have a later-than-usual dinner, relax, and then call it a day.

If I know that a system is unusually "wet" for whatever reason or that it has been open for a long time, I'll go for an overnight evacuation, if possible.

I, too, use a micron gauge to supplement the low-side gauge on my Manifold Gauge Set. And I change the oil in my vacuum pump after every second evacuation.
Thanks for this information. I guess I will have to re-evaluate my evacuation procedure. I don't see myself doing it over night though. Even though I change my vacuum pump oil after every use per the owner's manual, it's 16 years old and I'm not sure I trust it to run all night without periodic checks to make sure it hasn't broke down or something.
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sherqa
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Re: Evacuation Procedure

Post by sherqa »

Here in Middle East most of the local mechanics are using vacuum pump made from air-condition compressor. I am wondering will it pull sufficient vacuum ?
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JohnHere
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Re: Evacuation Procedure

Post by JohnHere »

The only way I can think of to test a vacuum pump is to attach a Manifold Gauge Set directly to the pump, run it, and see what it pulls. If you're close to sea level, a good pump should pull down to about 29.94 Inches of Mercury. At higher elevations, the vacuum reading will be correspondingly less.
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