Evacuation Procedure

[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.

[70monte]

"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.

[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 ?

[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.

[tony1963]

If the system has been open for any period of time, it contains moisture just like the atmosphere. Pulling a vacuum for an hour is typically sufficient.

There are diminishing returns and the longer the time, the less air and moisture will come out. My experience shows that you can achieve a full vacuum of 29 in about 5 minutes. Of course, keeping it under vacuum longer will boil the moisture. But, a full hour versus two hours is not going to remove twice as much moisture, maybe only less than 1% more. So, it is all relative.

You could, in theory, leave it under vacuum for a year or into infinity.

[swampy 6x6]

After reaching 500 micron at least 1 hr on the vac pump ,, using 4cfm or bigger 2 stage .
8 ---12 HRS if system been left open for any period of time
Bigger diameter the better for vac hoses

[JohnHere]

swampy 6x6: Note that this thread is more than one year old, so you probably won't receive a response.