What if air gets in when refilling A/C?

2002 Subaru Legacy L
A/C was putting out hardly any cool air. Got an A/C Pro kit: 20 oz bottle with guage. The guage has you set it according to the air
temperature. When I used the A/C Pro kit, lots of cool air came out the vents; however, according to the guage, the pressure was just barely touching the green mark and barely inside the lowest line of the temperature adjustment. The 20 oz can got used up. I got cool air but figured more pressure to get it a bit more in the green would be better.
So I got another can of A/C Pro (just the can since I already had the guage and hose from the first kit). That got the pressure to a tad into the green but wasn't a drastic change. The problem right after adding the 2nd can was I could hear a recurring whine inside the cabin. About every half minute there was a solid pitched whine. It'd come, it'd go away, but it was periodic. I also think there was a bit more of a clunking noise in the engine compartment but I'm not sure it if was just the engine at low idle not being smooth.
I read the instructions and do not recall them even telling me to charge the hose. That is, to attach the hose and guage, press in with something on the end of the hose to open the valve at the end, and squirt a charge from the can into the hose and then release the valve pin to shut it. So what happened is twice there was air in the hose that got injected into the car's A/C system. I don't think air in the A/C is a good thing.
So what could be the whining that I hear inside the cabin? Is it the air getting pushed around in the lines? Might it be the lube and sealant they mix in with the refridgerant?
I don't how accurate is the guage that comes with the A/C Pro kit. Maybe it's defective and I've got way too much coolant (pressure) in the system. In that case, maybe I could bleed some out. My recollection is 50 PSI is about right but I never got that close according to the guage. That's at high temperature. When I filled the first time, the temperature was 80F. The second time it was 70F.
At this point, discharging all the refridgerent from the car's A/C (assuming I can just press in on the valve to release the stuff, like a pin valve in a tire valve) and refilling it but this time pre-charging the hose. The first charge was $45 for the A/C Pro kit w/guage plus $15 for the 2nd can, for a total around $70. The car shop says they'll evacuate and recharge for $70-$120.
I have no way to evacuate the system (depressurize to remove water) and just did a simple recharge. I believe they said they'd evacuate at the price range they quoted (which fluctuates depending on how much freon they have to add). As I understand, there is a ultraviolet dye in the coolant that will let them find a leak. I have no UV lamps. So I might just let the shop do it.
I was curious as to what [bad] effect might be caused by injecting the air in the filler hose into the A/C system (and did it twice). And what might be the cause of the in-cabin periodic whining when the A/C is on after my recharging.
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You have grossly overfilled your system. It holds a TOTAL of 24 oz of refrigerant. You had some left before you started with the full can, so you were likely overfull by the time you got the first can in. Too much refrigerant will cause poor cooling too - and if it blows a seal you are in deep doo-doo- particularly if you are monkeying around under the hood when it lets go. SERIOUS frostbite!!!!!
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snipped-for-privacy@snyder.on.ca wrote:

I would've thought that more freon would mean more pressure. So the gauge means nothing when recharging? Why would they add a gauge if it was worthless?
They have you fill on the low side of the compressor. Is there a regulator that restricts the max pressure on the low side so that a gauge would never reflect the correct pressure in the entire system?
Why would they provide a gauge if pressure wasn't the measure of charge? There's no way to know how much is still in the system when adding more so there'd be no way to know if the 20 oz can in the kit or even if the 15 oz can was too much if recharge was measured by ounces.
Everything that I've read said to monitor the pressure using a gauge along with temperature compensation (and why there is a dial with min/max lines that gets adjusted according to the ambient temperature). While cars using the old R12 had a PSI rating of something like 200 PSI, the newer R134 is usually about 55 PSI for top end. It's not like the can is transparent with ounce marks so you could see how many ounces went in. Plus when recharging, you don't know how many ounces are already in the system.
After searching and wading through all the results, I found: http://www.techchoiceparts.com/refrigerant-and-oil-capacities/subaru . According to that article (though it only goes to 2001), the weight capacity of a Subie Legacy is about 24 oz. You can't get all the freon out of the can because once its pressure matches the system's pressure then there won't be any more transfer. So I'm guessing the 20 oz kit bottle and the 15 oz refill bottle probably added about 30 oz and that is a bit too much, plus there was probably some old freon still in the system.
If I bleed off some of the freon, would surrounding probe with a couple rags be sufficient to avoid the cold blast? Can something simple, like a probe or long metal pick be use to depress the fill valve to release some of the freon out of the system? Rather than guess how much to bleed off, I could just bleed it all and then use the 20 oz kit again. I have to wonder if pressure isn't how a recharge is measured then how would you know when using the 15 oz refill cans as to when you should stop filling? The gauge doesn't measure ounces, just PSI.
Seems all A/C systems will leak, something like 2 oz each year and why they have to get recharged after awhile. I also read that this leaking will let air into the system. So I have to wonder if the recharge kit's hose having air in it would really cause any problem. The reason water gets into the A/C system is that air gets in and carries water with it. Me recharging the system won't evacuate out any water that was there already and why I'm thinking my DIY job failed and I should have the shop do the job which includes evacuating the system.
Do I: - Release some freon and use the guage to see when it's back to to just touching the green area (where it was after adding the 20 oz kit can)? - Purge it all and start over with just the 20 oz kit can (which is about 4 ounces short of the capacity mentioned in the article)? - Give up and have the car shop do it?
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This is why you are smart to take it to someone who KNOWS how to charge AC. The only way that is LEGAL for a certified A/C repair person to charge an automotive AC system is by weight. Draw all of the refrigerant out, evacuate the system totally, then install the proper weight of refrigerant into the system. A lot of technicians who have the experience will charge by the guages (BOTH - not just low side) and get within ounces of the spec. I have installed and charged over 100 automotive AC systems, many of them charged from cans - and I have never wasted more than 1/2 oz of coolant per can. To get all of the refrigerant out of the can you put the can in hot water and shake it - evaporate all of the refrigerant out of the can and all you have is a few cubic inches of vapour left in the can.
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VanguardLH wrote:

enough said. IDK how it is legal to sell those things when it is illegal for a shop to....well....basically.....DO EVERYTHING WRONG
Hopefully the shop you bring it to, knows to check for the presence of sealant in the system, and will then refuse to work on it at all.
GW
and guage is not a word
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wrote:

Sorry to dissagree - but from http://dictionary.definitiondb.com/define/guage
Guage Noun
1.A measure; a standard of measure; an instrument to determine dimensions, distance, or capacity; a standard. ?The record of philosophy vis-à-vis silence is generally dismal, as good a gauge as any to its overall failure.
2.An act of measuring.
3.Any instrument for ascertaining or regulating the level, state, dimensions or forms of things; as, a rain gauge; a steam gauge.
4.A thickness of sheet metal or wire designated by any of several numbering schemes.
5.The distance between the rails of a railway.
6.A semi-norm; a function that assigns a non-negative size to all vectors in a vector space.
Guage Verb
1.To measure or determine usually with a gauge; to measure the capacity, character, or ability of; to estimate; to judge of.
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Good god, do you really give credence to a site that thinks a misspelling is a real word?
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Geoff Welsh wrote:

Why would they care since they will be evacuating the system of EVERYTHING in there? Or don't they do a full evacuate? They can't blow out the system?

Let's focus on the issue, not on a typo. You missed that I mispelled "refrigerant".
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MOST of the sealants out there will do a real number on the reclaimer filters - so most carefull techicians don't want anything to do with them.. In my opinion they are a "last ditch" solution. The car will be scrap next year, but it's too bloody hot to run without AC??? Throw a can of sealer at it and see if it sticks. If it works, you are cool untill it fails again - If it doesn't work, at least it was cheap, but you now have no AC untill you scrap the vehicle.
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On Tuesday, August 5, 2014 5:38:03 PM UTC-5, VanguardLH wrote:

You probably need 2 o-rings at the compressor, you may need to rent (borrow actually) a vacuum pump from AutoZone and re-fill with 22 or ozs. of refrigerant.
Or, just take the car to a pro.
You need to read this; http://www.subaruoutback.org/forums/99-do-yourself-illustrated-guides/43428-diy-c-air-conditioning-leak-refrigerant-repair-5-less-15-minutes-less.html?highlight=compressor+o-rings
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