here and here) about automotive air conditioning. This post is not redundant, though. It is intended to be a more comprehensive description of how it is possible to resurrect a nonfunctional car air conditioner. Possible, but not necessarily legal. I know that the use of hydrocarbon refrigerants such as propane, isobutane and commercially available blends thereof is outlawed in some US states, and direct replacement of R12 with such refrigerants is illegal throughout the US. I also believe that mixing refrigerants directly in the AC system (as opposed to mixing in a separate container) is illegal in the US. If you are in Canada, you may be subject to much less-restrictive law. Either way, you are responsible for knowing what you can and cannot legally do. This information is therefore not a recommendation, but educational only.
Lots of us frugal types drive a vehicle old enough to have left the factory with an R12 based air conditioning system. As you may remember, sometime around 1994 the governments of the US and most other countries banned further production of R12 Freon refrigerant. R134 replaced R12 in new cars in the US and most of the world, and automotive repair shops did big business converting existing cars to R134a when they needed service. In fact, we owners of R12-based systems were told that R134a was the only way to go, other than paying increasingly high prices for dwindling R12 supplies. The big problem was that cheap R134a conversions often resulted in major air conditioning system failure in short order, necessitating a complete system rebuild. The only sure way to avoid this, we were (and still are) told, was to rebuild most of the system to begin with. This included replacement of all hoses with the new barrier hoses because R134a, with its much smaller molecule size as compared to R12, leaked out much faster than R12 did. Some people didn't convert, though. I was one of those. I and others like me heard the horror stories of failures and huge repair bills resulting from simple 134a conversions, and balked at paying a thousand bucks to do it "right." So we paid 900% more for R12 when we could afford it, not to mention paying shop labor charges because another new law required certification and licensing to even purchase R12. When that charge of R12 leaked out, if we didn't have $300 to have it recharged again we fell back on "4-60 air conditioning" (four windows down, 60 mph). A few people even drove their cars to Mexico whenever the AC quit working, to get a cheap R12 recharge where it was still unrestricted. About this time, I started hearing stories of some people simply recharging their AC with propane. At first glance it seemed like a really bad idea, and a lot of people get bent out of shape if anyone even alludes to it in their presence. Just do a search on some automotive forums and you will see what I mean. But in some countries such as Japan and Germany, hydrocarbon refrigerants have been and are used extensively with few to no problems. In fact, although I haven't verified it, I have heard references to BMW using HC refrigerants in some markets after the R12 ban. Straight propane works pretty well as a refrigerant, and being lighter than CFCs, it takes less than half (closer to a third) the amount by weight that the same system would use of R12 or 134. This helps a bit with the safety concerns when you consider that the typical car AC only needs one pound or less of propane for a complete charge. The problem is that EPA expressly forbids the use of any unapproved refrigerant, including propane, as a direct replacement for R12. They do however have a list of refrigerants that are approved as a replacement for R12. Among these are Freeze-12, R406a, Free Zone, Ikon 12, SP34E, Autofrost, and a few others in addition to R134a. To the best of my understanding, once a former R12 system is converted to one of these approved refrigerants, later conversion to propane or other hydrocarbon refrigerant no longer constitutes a conversion from R12. Therein is the gray zone that allows the sale of prepackaged hydrocarbon refrigerants such as HC-12a: EPA doesn't specifically ban it (as of yet, as far as I have been able to ascertain); only its use to directly replace R12. The bottom line is that as far as I can tell, it is not necessary to go for a complete system rebuild (as with R134a) to convert from R12. Just do the far simpler and cheaper conversion to an approved refrigerant that is actually designed and approved to directly replace R12, such as the well known Freeze-12. Contrary to popular belief, it is not hydrocarbon-based. In fact, it is mostly R134a, but has some other stuff added to make it live with the mineral oil in R12 systems. The point is, it is cheaper than R12; and if it leaks out too quickly for your liking or you simply want to use something cheaper, you will no longer be replacing R12. You did that last time, when you switched to Freeze-12 (or R406a, or whatever).
By the way, a search of ebay will turn up sellers who list refrigerants that they claim are fully compatible drop-in replacements for R12, R134a, R22 and just about anything else, with no changes necessary. These products are propane/isobutane blends just like you can make at home. A couple of examples are Enviro-safe and Super Freeze. Both of these are marketed as direct replacements for R12. If you go to the manufacturer's website you might find a cryptic reference to "first generation" and "second generation" R12 replacements. That is just their way of referencing the EPA law without coming right out and telling you that using their product as a direct replacement for R12 is illegal. I personally have no problem with either those manufacturers and sellers, or DIYers who do convert directly to non-approved refrigerants. More power to them if they get away with it. In my opinion, that is one of many stupid laws anyway, that unnecessarily hinder individuals and small businesses in order to profit the government and the big corporations that are in bed with the government. But I do believe in covering my own assets, and helping others do the same. Therefore, convert to an approved replacement before you even seriously consider using an unapproved refrigerant.
Now, more about those HC refrigerants. As mentioned, some people did and do use straight propane. There are a couple of things to consider about using propane. First, it is best to steer clear of the bulk tanks, like the 20-pounder that powers your grill or the appliances in your RV. That stuff just has too much moisture in it. A better plan is to use the disposable bottles like you buy for torches, lanterns and camp stoves. At 14.1 to 16 ounces, they are also just about the right size for a full fill. Second, be aware that propane will run at higher pressure (on the high side) than R12, although lower than R134a. That is ok and lots of folks accept that, but the prepackaged HC refrigerants like HC12a, Duracool 12a, OZ 12, etcetera add isobutane to the mix. The isobutane lowers the head pressure to the same as R12, and the resultant mix is actually more efficient (cools better and with less horsepower input) than R12, and substantially more than R134a. The ideal mixture is 79% propane and 21% isobutane. This is the mix that the above-mentioned HC refrigerants all use, and is what the EPA calls "Hydrocarbon Blend B." The thing is, you can buy it for about $10 per can and use an R134a charge hose, but you will have to buy it online and pay shipping. But what some other people do, and what I am about to describe here, is mix it at home. Before I go on, just let me say that this mix is fully compatible with R12 and R134a, so if there is any residual refrigerant of either type in your system, it won't wreck your system. In fact, some people have illegally topped off existing systems with propane, with no ill effects noted. But don't do that. You are supposed to evacuate and capture the existing charge of whatever might be in there before recharging with anything. It also makes the measurements easier, although those measurements are in no way critical. Here is what you need, should you be planning to try this:
- A low-side fill hose with gauge. I bought a cheap, $22 manifold gauge set and am amazed at the quality for the price. I have included a link to the same set, below. You will also need an adapter to fit from the low-side hose to the R134a connectors you had to retrofit when you converted from R12, if your vehicle originally used R12.
- A way to connect the disposable propane tank to the charge line. I read accounts of people buying a brass propane torch head, hacksawing off part of the tube, drilling out regulator valves, and threading the tube to accept the threads on the hose. I have a much better and easier way to do it, which I will detail a bit later.
- A can side tapper. This is for the isobutane.
- Two, 1.48-ounce cans of Ronson Multi-Fill Ultra Butane Fuel. I got these at Walmart. Make sure the ingredient is listed as "Isobutane, CAS #75-28-5." I read all kinds of stuff about searching for backpacking stove gas that contains a certain percentage of isobutane to propane, avoiding the ones that have butane instead of isobutane, etc. But then I found this, which is cheaper ($2.47 a can), more readily available, and is pure isobutane.
- One, 14.1 ounce cylinder of propane. I already had one, but two or three bucks should get you a new one.
- A vacuum pump. You can build your own, or buy one.
Now, what I did after having the remaining Freeze-12 evacuated from my system by a friend who has a license, was to simply refill with propane. Straight propane does run higher head pressures than the refrigerant that the system was designed for, but according the information I found there is no problem as long as you monitor the low-side pressure as you fill the system, and do not allow it to exceed 60 psi when the compressor is running. Here is how I did it:
- Connect the fill hose to my propane valve (from the torch kit). Before I did this, I made sure the valve was closed. I also made sure both valves on the gauge set were closed.
- Tighten the fittings on the gauge set, then open the propane valve. Crack open the low-side valve on the gauge set just long enough to purge the air, but not long enough to release propane. Re-close tightly.
- Connect the low-side hose to the low-side port of the system.
- Start the engine, lower the windows, and switch on the air conditioner to its maximum-cold setting. Yes, I know that the compressor will not cycle. Bear with me.
- Set the throttle at a fast idle by whatever means available. If necessary, utilize a helper for this part. Allow the engine to run for five minutes or so, then:
- Locate the sight glass (usually near or on the accumulator) and clean it with a shop rag. Hold the propane tank upside down and slowly open the low-side valve of the gauge set. If the gauge set has a sight glass (mine does), watch it and adjust the valve so that some liquid is passing the sight glass, but do not allow it to become fully liquid.
- When the system reaches its minimum pressure threshold, the compressor will begin cycling. The gauge will fluctuate between high pressure (when the compressor is not running) and lower pressure (when it is running). The low pressure is the important reading. The compressor will initially cycle on and off rapidly, and will run for longer and longer periods as the system fills.
- When the pressure reaches 28 psi, start also watching the sight glass (of the system, not the gauge set. I have been keeping an eye on the gauge set sight glass continuously, to monitor the propane flow.). Unlike charging with the original refrigerant, the sight glass should never become fully clear. If it does, the system is overfilled.
- Occasionally stop, reach into the passenger compartment and feel the output of the vents. It should be getting colder.
- When the line between the evaporator and accumulator is cold, the sight glass shows liquid with bubbles in it and the output of the vents is cold, stop filling and close the low-side and propane valves. The low-side pressure should be at least 28 psi, but less than 60 psi. At this point I remove the gauge set, close the hood and start enjoying my air conditioning.
- Connect the propane valve to the empty tank. Connect the vacuum pump to the valve. Pull a vacuum on the tank, then close the valve and disconnect the vacuum pump.
- Connect the can tapper to the fill hose. Connect the fill hose to the propane valve.
- Place a 1.48 oz can of isobutane (Ronson Multi-Fill Ultra Butane Fuel) in the can side tapper. I had to use a small wood block as a spacer to make it work. Squeeze the handles to puncture the can, and hold them closed while opening the propane valve and allowing the contents to empty into the propane tank. Close the propane valve. Remove the empty isobutane can and repeat the procedure with the second can.
- Remove the can tapper and replace it with the second propane valve. Attach a fresh, full 14.1 oz propane tank to the second valve.
- Open both valves and hold the full 14.1 oz tank upside down above the 16 oz tank until all of the propane drains into the 16 oz tank.
- Use the 16 oz tank of propane/isobutane mixture to charge the air conditioning system, in the same manner as described for straight propane.