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After having the shop that repaired my R12 AC system last year mildly to moderately under-fill it (before it was ice-cold; now it cuts the humidity ok but only gets cool only after 10-20 minutes of highway driving) I got the necessary certification and am planning to top the system off to get it up to the level it should have been filled to. In order to avoid doing something stupid and releasing a bunch into the atmosphere (and wasting money), I want to make sure I'm prepared with the right tools before I start.

It looks like all the small R12 cans you can get are sealed and require a tap (as opposed to DIY R134a cans with valves on them). I've seen top- and side-tap devices advertised for this; some examples:

How do they work? Do you latch the device onto the can first then twist the tap to puncture the can, and loosen it again to allow it to flow? How do you seal it to prevent leftover coolant from slowly escaping? Do you need a secondary shutoff valve of some sort attached?

Aside from this, are there other tools I need or should have on hand? I do have a set of hoses/gauges already, but in the past (R134a systems) I've just gone by feel of the air blowing out to judge when it's suitably full.

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  • Why not just convert it over to R134a? I'd suspect the kit to do this would be less than purchasing one can of R12.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    May 28, 2017 at 21:28
  • I can get R12 cans for $25 plus shipping. Conversion (done right) is a huge ordeal that involves thoroughly evacuating and flushing the system to make sure no oils incompatible with R134a remain; it may also involve replacement of old gaskets that will fail after the switch. Plus R134a is a significantly less efficient refrigerant.
    – R.. GitHub STOP HELPING ICE
    May 28, 2017 at 21:43
  • Less efficient, yes; Significantly less efficient I wouldn't say. No clue where you're getting cans of R12 for $25. Most I've seen are in excess of $100 each. Just a suggestion.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    May 28, 2017 at 22:27
  • On ebay individual 12oz cans are almost always under $60, and you can often find bundles of multiple cans that come out to $35 or less per can. These are trends I've observed by considering doing R12 AC work myself over several years, not just the current prices. Maybe at one point it the prices were higher; I wouldn't be surprised if reduced demand (fewer unconverted older vehicles in service) has caused the prices to decline.
    – R.. GitHub STOP HELPING ICE
    May 28, 2017 at 22:31
  • As for efficiency it's been a long time since I looked at numbers, so it might not be a big deal. But it's still rather unappealing to do a big overhaul with risks of additional system failures for the sake of something that's not even an improvement, rather mildly worse, just because the refrigerant is easier to obtain. And I've got obtaining it covered anyway. I just want to know what I'm doing so I use it responsibly and don't cause environmental harm or waste money.
    – R.. GitHub STOP HELPING ICE
    May 28, 2017 at 22:33

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I ended up using one of the can taps that attaches on the top, with a metal cap containing an O-ring so that the can could be sealed at the threaded connection, beyond the minimal level of seal provided by the tap. I was surprised at the lack of actual locking in the "clamp" that attaches around the neck of the can, though. It feels like you could knock it loose and send the whole thing flying off just by touching it wrong. Overall the process was uneventful and went fine, though.

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