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A concern that comes up regularly when troubleshooting A/C problems is whether an A/C system has too little refrigerant (hello leaks) or too much of it (hello overcharging).

The traditional way to do this involves drawing out all the refrigerant (often with expensive, specialist equipment), which adds considerable overhead to a DIY-er like me as I then have to worry about sourcing compressor oil or recycling the existing refrigerant.

So, is there an environmentally-conscious way to determine the amount of refrigerant present inside an A/C system that does not rely on complete evacuation?

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You can draw out all refrigerant from a system with no expensive equipment. All you need is a hose (preferably with manifold gauge), a suitable storage tank, a decently insulated container (like a large cooler) that it fits mostly inside, and dry ice to pack around it, around 10 pounds, or less if you have a liquid acetone or alcohol bath to transfer the heat more efficiently out of the tank. Dry ice is around -70°C, and automotive refrigerants liquefy around -25-30°C, so all (modulo some extremely low vapor pressure) the refrigerant will liquefy in the tank; you can confirm this by observing vacuum on your manifold gauges, which should match the vapor pressure of your refrigerant at whatever temperature you can get the tank down to.

Dry ice will run you about $2/lb and can be purchased at Kroger and some other grocery stores.

You can get a 30 lb tank for around $80-100. I got one off Amazon. In theory, if you have an empty refill tank that can hold at least as much as your system, you could use it. This is of questionable legality, and dangerous if there's any risk you might overfill it (assuming it might return to a gaseous state before you move it back, in which case an overfilled tank could explode), but it's not as bad as actually pumping hot pressurized gas into such a tank.

Here's a picture of the setup I've used, in progress:

enter image description here

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  • It seems like you've gone through this exercise before. Am I right in saying that you will be left with some residual refrigerant inside the system with this technique?
    – Zaid
    Sep 15, 2018 at 6:33
  • @Zaid: It depends on what you mean by "some". There's always some vapor pressure, but it's very low. You should see at least 25 in of vacuum, ideally closer to 29. If you don't, it probably means there's something (air) that doesn't condense to a liquid contaminating the system.
    – R.. GitHub STOP HELPING ICE
    Sep 15, 2018 at 6:57
  • If you figure the system is normally something like 60psig, 25 in of vacuum would mean you've evacuated all but about 1/30 of it, and 29 in would mean all but about 1/150 of it (<1%).
    – R.. GitHub STOP HELPING ICE
    Sep 15, 2018 at 7:08
  • This has results that are much better ie 1% compared to about the 10% of the other answer.
    – Solar Mike
    Sep 15, 2018 at 8:42
  • What I'm wondering is, how does this answer the question? The question specifically asks "... without evacuating the entire system ..." While your method may be accurate and can be done by the DIY-er, you are evacuating the system to make it happen.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Sep 15, 2018 at 12:29

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