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Old 08-30-2007, 10:40 PM   #1
NeoRules
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Default AC recharge.. How long to pull vacuum?

I think my system is shot... I hooked up my old r12 gauges on the high and low side... hooked up the vacuum pump and it only pulls 10 hg of vacuum even after 30 mins.... I haven't used it in sooooo long that I can't remember how long I pulled vacuum on american cars... but a half hour seemed to come to mind.. but I think that might be a little on the low side.....

Anybody remember...???
I have both valves open and the blue on high and red on low (I think...) anyway they are on the correct high side low side and the yellow in the middle is hooked to the vacuum.....
My mighty giant shop compressor is working a lot and it seems that it isn't pulling anything ... Can't here a leak cause it's way to noisey out there.....
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Old 08-30-2007, 10:55 PM   #2
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mine was recharged in a matter of 5-10 minutes. unlesss i dont now what ur talking about. which is very likley
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Old 08-30-2007, 10:59 PM   #3
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he's talking about leak testing. before you recharge your ac you'll have to pull a vacuum to see if there are any leaks anywhere, that way you know whether or not it is safe to charge your air conditioning without running the risk of leaking r12 everywhere. 1/2 hour sounds about correct to me.
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Old 08-30-2007, 11:02 PM   #4
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he's talking about leak testing. before you recharge your ac you'll have to pull a vacuum to see if there are any leaks anywhere, that way you know whether or not it is safe to charge your air conditioning without running the risk of leaking r12 everywhere. 1/2 hour sounds about correct to me.
Yeah... crap.... the high side pulls a vacuum but when I open the low side valve it drops down to 10 and stays there..... now I gotta do the leak thing.... I hate that on small cars....

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Old 08-30-2007, 11:05 PM   #5
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anybody up north want a 944 turbo with no AC????
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Old 08-30-2007, 11:07 PM   #6
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o sorry. how cold is the air supposed to be? i have mine set on high and the coldest. but it only seems mildly cool. and i just had it recharged
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Old 08-30-2007, 11:16 PM   #7
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At work (not a car repair shop) we pull down to a full vacuum on both sides. The whole system has to be sucked down as low as 30mm of mercury on the gauge. As soon as it's down that low, close the gauge valves and shut down the vacuum pump. Watch the gauges, they should NOT lose vacuum. AC systems are closed systems. If it does not hold a vacuum, it's time to leak search. Probably the compressor seals.

We've had to work on about 4 HVAC units here at work and are waiting on a $5K compressor for out main building. I've been getting great review since I haven't done it in a while.

Last edited by ejsaenz; 08-30-2007 at 11:17 PM. Reason: made less confusing...and spelling...
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Old 08-31-2007, 12:08 AM   #8
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At work (not a car repair shop) we pull down to a full vacuum on both sides. The whole system has to be sucked down as low as 30mm of mercury on the gauge. As soon as it's down that low, close the gauge valves and shut down the vacuum pump. Watch the gauges, they should NOT lose vacuum. AC systems are closed systems. If it does not hold a vacuum, it's time to leak search. Probably the compressor seals.

We've had to work on about 4 HVAC units here at work and are waiting on a $5K compressor for out main building. I've been getting great review since I haven't done it in a while.
you pull down the high side and the low side seperatly?
I was trying to pull both sides at once.... Since it is a closed system.
Should I do each side individually?
and how would I do that since I have only one vacuum gauge on the low side.... JC
Thanks JC
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Old 08-31-2007, 12:13 AM   #9
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pulled mine down to vac in a matter of a few minutes. Left it sit for ten minutes and it didnt leak down-after i replaced the seals on the compressor hoses- then charged w/ 134a- its colder than my truck and has been for three months!
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Old 08-31-2007, 12:47 AM   #10
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The high and low sides both get pulled down at the same time because it is all one interconnected system. Pulling vacuum on both ports at the same time will not hurt anything. Main thing is to ensure it holds that vacuum for a period of time after the vacuum pump is shut off. Are you using a vacuum pump that runs off compressor air? They only pull so much vacuum, not as good as a mechanical pump. Regardless that is what I used and it worked well enough for a home job. I felt like I was going to burn up my air compressor because it was running for so long while pulling the vacuum though.
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Old 08-31-2007, 02:10 AM   #11
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Quote:
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The high and low sides both get pulled down at the same time because it is all one interconnected system. Pulling vacuum on both ports at the same time will not hurt anything. Main thing is to ensure it holds that vacuum for a period of time after the vacuum pump is shut off. Are you using a vacuum pump that runs off compressor air? They only pull so much vacuum, not as good as a mechanical pump. Regardless that is what I used and it worked well enough for a home job. I felt like I was going to burn up my air compressor because it was running for so long while pulling the vacuum though.
yes that is what I am using.... and I have a really large compressor and it still cycles a bit.....
I should be able to get better than ten though....
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Old 08-31-2007, 03:13 AM   #12
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pull vac for an hour and then wait an hour or overnight before charging if you have the time, if not wait an hour and check your gauges again.
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Old 08-31-2007, 10:04 AM   #13
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Dude... at the dealership we vac fro 10 mins, leak check for 10 mins then charge, you system needs to be pulled to 30hg to boil the water out of the system, hold that for 10 mins, if you dont see any leakage, charge that baby... When you inject your oil, use the oil that has dye, that way if you do have that very small hole that takes 3 months to bleed out you can just black light it.

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Old 09-03-2007, 07:27 PM   #14
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ok... charged 2 cans... have 0 on the high side and 33 on the low side...
Even after I jumper the high side switch I get 0 pressure on the high side....

What usually fails first the receiver drier or what????
If I am getting no high side pressure but the system doesn't leak down where is the problem????
Thanks JC
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Old 09-03-2007, 08:19 PM   #15
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You have a blockage in the system somewhere, could be the receiver drier, metering device, or just about anything else. With 2 cans in you should have WAY more than 33lbs, is the compressor cycling? Are you sure you are getting a good connection to the high side port?
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Old 09-03-2007, 08:19 PM
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ac, air, auto, conditioning, high, long, low, pull, pulling, recharge, running, side, truck, vaccum, vacuum

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