It possibly will not help if your A/C does not work at all as that may indicate other problems such as a leak maybe because seals have dried out during a lengthy period of not using the AC.
For me, a few years back I went down this route on an old car and didn't work as expected on a A/C system that hadn't been maintained for years. Depending where the access points to A/C are it can be a bit of a PITA. On my previous car it was wheel off, wheel arch liner removal and limited access afterwards. Possibly a lot more access if the car was on a lift but not when working on a driveway :)
My local car A/C recon service charged £60 (incl VAT) to do it properly. They had the equipment to automatically evacuate the old gas, vacuum dry the system as well as recharging with gas, oil and to add (leak) trace dye. They said that they added the dye to every recharge cover any short term returns where the dye highlights any problems that may not have been found during the recharge.
It's the intermediate processes of getting any water out and drying the system that is as important as the re-gassing. I was lucky on my previous car that no leak was detected but the amount of gas in the system was very low. I got a print-out of gas out, gas in and other various parameters measured during the process.
I found when using the can method I was still left with a lot in the can, less than I started with but still a lot. Subsequently getting it done by a re-gas service showed that the system was still very low on gas. Perhaps the pressure in the can alone isn't enough to recharge the complete system? When the machines do the task first they generate a vacuum both to dry the system and detect leaks and use this vacuum to help replace the gas.
One of the reasons CO2 is not viable, is building the compressor and plumbing. "CO2 doesn't want to be a refrigerator gas" :-) It has excellent pollution characteristics (compared to R12). But it's a nightmare for the person trying to design a fridge with it.
R12 was beautiful stuff. The refrigeration works at relatively low pressure. The units could function for years. My central air with R12, it lasted for 40 years, and in the 20 years I used it, it *never* needed to be recharged.
This means, while the "badness rating" might be 9000, it hardly ever leaked.
The newer ones, they run at higher pressure, a charge doesn't stay in the unit, but, the "badness rating" is lower. The only part getting dinged, is your wallet. (To recharge the central air of the current system, cost me $1000 including a new "A" coil to replace the brand new one in a four year old system.)
The recovery equipment, uses a zeolite cannister. The vacuum pump to evacuate the old material, that part probably doesn't change from one refrigerant to another. Perhaps a separate machine could be used, to avoid contamination from one system design to another. I don't really see why that's necessary though, except for people who aren't HVAC trained and "just want to run a machine".
You would need a different zeolite for R1234 versus R134a. The neat thing about the zeolite, is the gas bonds to it very well, so by the time it's "pulled" by the vacuum pump, the zeolite has absorbed all of it. You hardly have to screw the cap on the bottle. Back at the factory, the zeolite is "cooked" to release the gas back into the factory vacuum tree. The purpose of zeolite, is so whatever refrigerant is being used, it *doesn't* go into the atmosphere.
But based on the leakage rate, and the number of times these systems need to be refilled, using zeolite is pretty silly. It was different in the R12 era, because when they would recover the charge, the machine was probably still full and you could recover it without any pollution at all. Whereas today, the modern higher pressure refrigerants, they're just continually leaking through tiny pinholes in the copper. The pinholes come from stuff like exposure to formic acid.
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When it comes to flammable gases, each gas when it explodes, has a different level of "shock wave". I tried to Google, but can't find a table right now of typical values. Some materials you can take inside a house or garage, can "launch you through a window" when they go off. For example, some idiots who took a car petrol tank into the living room, they flew fifty feet through the livingroom window... and survived. There's less damage in buildings, if there are windows to release the pressure. There have been a few incidents here though, where houses were reduced to splinters by an explosion inside. And shock damage to all the adjacent houses (in some cases those are a write-off too).
This is one of the reasons, the "size of charge" in the table, the number of grams or ounces, matters. They're attempting to prevent trouble, by reducing the fuel load. Maybe one cannister, if injected into the car system, wouldn't be a deadly disaster if it leaked. But if you did 100% of the charge with the flammable gas, there'd be more potential for trouble (you vacuumed down the car system and did a 100% fill with something nasty).
When you blend gases like that, one gas may preferentially liquify compared to the other. And this changes the temperature behavior of the system. A professional would know more about the outcome than I would, but there's going to be some sort of phase diagram to predict the outcome.
"The most notable fire involving a refrigerator with flammable refrigerant was in London at the Grenfell Tower, which killed 72 occupants. This fire apparently originated with a refrigerator; however, subsequent reporting on Nov. 27, 2018, by BBC News quotes Dr. J Duncan Glover, "The overheating connector in my opinion was the first event that started burning the insulation on the wires that led to the short circuit."
I suspect most of comment is justified. It was a stitch-up between interested parties to use R-1234YF to make loadsamoney. It's why most have moved to hydrocarbons rather than an alternative protected by patent.
When the patent runs out I'm sure there'll be some reason to use something more exotic.
The pictures I've seen so far of fridges charged with a flammable gas, the damage is usually limited to the kitchen. I don't know if any houses have burned down because of it.
If you do choose to add a flammable gas to the car system, and later you decide to take it for an AC service, don't forget to tell the guy what you added. The vacuum pump, normally nothing would come out of the vacuum pump exhaust pipe (no R134A) because that gas is captured in the zeolite cylinder. But the propane would not be captured by the zeolite, and so the propane comes out the vacuum pump exhaust tube at a slow rate. And you would not want the vacuum pump exhaust tube to "vent" into the service bay. It should vent outdoors. And preferably not in an area where the mechanics have their smoke break.
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