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05-25-2013, 03:13 AM
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The Quest for a 100 percent DIY A-C Setup
I have been working on a conversion of a R4 compressor to a Sanden compressor on my diesel SL and in that process have done a substantial amount of research on the various refrigerants that are available, with the goal of finding a setup that is capable of being 100% maintained by a DIYer. The information presented here is for informational and entertainment purposes only, and is designed to open up lines of thinking that might not otherwise be considered.
I would never advocate breaking the law, but obviously people do all manner of illegal things with their cars from speeding and running red lights, to removing EGR equipment to driving without a license or insurance, texting or calling while driving, driving under the influence, and so forth and so on. You break the law and get caught, be prepared to pay the consequences. Also I'm not intending this thread to be advocating for or against any strategy or system, and I would hope that any discussion that ensues would be focused on factual information and not opinion - and that any person making a decision outside the norm be respected and not attacked. At the end of the day, each person can and should make their own decision about what strategies they use and the risks they are willing to take to achieve their own personal DIY goals. Isn't that the goal of this forum? The Big Two If someone were to talk to an A/C shop, they would be led to believe that there are only two automotive refrigerants that are available - R12 and R134a. R12 was the original refrigerant (freon) that was deemed to be bad for the atmosphere largely through legislative fiat. R12 is generally not a DIY refrigerant for two reasons: First, it must be recovered and may not be vented into the atmosphere and second, cannot be bought without a license. Notwithstanding that reality, DIYers can spend $20 or so and take an open book test and get the technician license to be able to legally use R12, but most DIYers cannot afford the expensive equipment to be able to legally recover. The alternative to R12 is currently R134a, which is a suitable refrigerant for systems designed specifically for this refrigerant, but not generally a good replacement for an R12 system because of its higher head pressure and less efficient cooling properties. So a DIYer is generally faced with a choice of having someone else maintain their system or retrofit to a R134a system and live with the lower performance. Starting with an R12 system, a DIYer can make a conversion to 134a in a relatively straightforward manner. Provided that a system is either empty through leakage, catastrophic failure, illegally vented or recovered at an AC shop, a DIYer can do the retrofit to 134a as a DIY project. Ideally, the system should be flushed, the expansion valve replaced, a new receiver/dryer installed, hoses and o-rings replaced, oil replaced with a compatible oil, vacuumed and leak tested and then charged. The R12 fittings need to be replaced with 134a compatible fittings. (Details on this process can be found in threads across the net). The selection of an appropriate oil is a subject beyond the scope of this document. Starting with a 134a system, a DIYer can maintain the system without any real problems as 134a is available almost anywhere in convenient packaging designed to be handled by a DIYer. But we have a very interesting problem with 134a that prevents it being a true DIY system. The law requires that when working on a system, the refrigerant must be recovered and may not be vented to the atmosphere. All automotive A/C shops have equipment designed to recover both R12 and R134a and virtually none have any other capability. This brings us to a very interesting situation. A DIYer would like to be able to maintain the system without having to bring it to a shop to have the refrigerant recovered every time they need to work on it. R134a is a fascinating material that changes its characteristics depending on the vessel in which it resides! If it resides in an automotive AC system, it is a very dangerous and polluting material that must be handled by professionals with special equipment that prevent it from getting into the atmosphere. In fact if you look at a typical MSDS for 134a used in automotive AC systems you will see descriptions and warnings like First Aid MeasuresHowever 134a is one of two refrigerants that are used as the "air" in Dusters. In this environment, we see descriptions like "removes microscopic dust, lint and foreign particles. Cleans computers and keyboards, photographic and audio/video equipment - Ozone safe, non-voc, non-flammable, non-conductive..." Eco-friendly and safe - what could be better. So we have a fascinating conundrum where 134a in a duster can is designed and sold to be vented to the atmosphere in the context of keeping computers and other electronics clean, whereas 134a in an automotive system cannot be vented to the atmosphere under penalty of $25000 fine. In a process that can only be deemed alchemy, in one container (an AC system) the product is dangerous and regulated, yet the instant it comes in contact with a duster can, it is acceptable and encouraged to vent to the atmosphere, preferably dispatching some keyboard dust in the process. (I have attempted to determine exactly which component of an automotive AC system makes the 134a so dangerous, and I believe it is the desiccant in the dryer. Everything else is just metal and rubber, not unlike the components of the duster can.) This situation is kind of like the old saying about a thermos bottle - how does it know to keep the hot things hot and the cold things cold? How does the 134a itself know where it resides so it can change its fundamental characteristics from dangerous to benign? So understanding this principle, a DIY person can easily create their very own simple and low-cost (and dare I say, magic) recovery system. By creating a recovery hose from a 134a fitting on the auto AC system and connecting it to an empty 134a duster can, through the magic of alchemy, the 134a refrigerant is transformed from an evil and dangerous gas, to a safe and environmentally friendly dusting agent for cleaning a computer. This transformation process happens in an instant, so there is no need to actually store the gas, it can be vented immediately as a dusting agent from the duster can.  A person making decisions purely on logic, might feel entirely justified in venting 134a directly to the atmosphere without using the magic duster can, but would be well advised to do so outside the view of of any other human and certainly not disclose this action in any manner. What About Other Refrigerants? There are literally scores of refrigerants. An interested reader is directed to this page for a partial list - List of refrigerants - Wikipedia, the free encyclopedia In fact, the types of refrigerants is myriad - CFC, CFO, HCFC, HCFO, HFC, HFO, HCC, HCO, HC, HO, PFC, PFO, PFC, PFO, PCC, PCO and H among others. Not all, in fact most, refrigerants are not appropriate for automotive use - either because of physical attributes or because of undesirable characteristics or because of cost. But there are some fascinating alternatives to R12 and R134a that can be used with varying degrees of legality and desirability and effectiveness. Making no value judgements, recommendations or assertions, the reader is directed to the following options as interesting subjects for research and consideration. R-290 (Propane) - Propane is a refrigerant that is cheap, highly efficient and easily used within automotive system. Persons considering propane are cautioned against using propane fuel that is readily available in camping bottles or in heating cannisters or as vehicle fuel. This "propane" is quite impure with water and other hydrocarbons present in significant concentrations that can seriously degrade AC systems. Refrigerant grade propane should be used if this is considered. Propane can be vented so no recovery issues exist. EnviroSafe (propane/isobutane) - EnviroSafe is a proprietary mix of hydrocarbons that is optimized for automotive use. It is legal for conversion from 134a systems but not from R12 systems. This is a legal technicality not grounded in any practical or physical reality. Some say that an R12 system that has been converted to 134a can be legally converted. Envirosafe can be vented so no recovery issues exist. While not legal, EnvoroSafe is entirely compatible to be added to an existing R-12 or R-134a system (topping off). DuraCool (propane/isobutane??) - DuraCool is a proprietary refrigerant predomanintly or entirely hydrocarbon based. DuraCool can be vented so no recovery issues exist. R-152a (1,1-Difluroethane) - This is a fascinating material that is a potential replacement for 134a when that is ultimately phased out. Amazingly, this product is what is contained in dusters as well. In fact a quick YouTube search for "Duster as Refrigerant" will yield some fascinating videos about how to charge an A/C system with duster propellant. R-152 has one undesirable characteristic and that is if it does catch fire, the byproduct is HF a very poisionous acid gas that is quite nasty. Future systems will likely be double loop systems that can keep the R-152a outside the cabin. R-1234yf (2,3,3,3-Tetrafluoropropene) - Another potential replacement for R134a. There are some undesirable properties of this refrigerant that have caused MB to have come out against adopting this refrigerant. R-600a (butane) - Like propane, butane is a good refrigerant option. Can be vented so no recovery issues exist. Some modification to the system may be necessary because of pressure differences. R-414a (mixture of HCFCs) - Brands such as GHG-X4, Autofrost, Chill-It R-414b (mixture of HCFCs) - Brands inlcude HotShot, KarKool Freeze 12 (mixture of 134a and R-142) - Freeze 12 is one of many 134a blends Any discussion of HC based refrigerants inevitably comes around to flammability. While there have been no documented cases of HC refrigerants catching fire it is not a zero-risk proposition, though many (or even most) believe the risk to be so low as to be negligible... and others believe the risk is too much to bear. The bottom line is that there is no one ideal refrigerant. All refrigerants have undesirable characteristics. Highly efficient refrigerant gasses like CO2 and NH3 are undesirable because of either poisonous characteristics or extremely high head pressures. Regardless of the path a DIYer takes, ensure that the system is clearly labelled to prevent the inadvertent contamination of commercial recovery systems in the future that may not test for the refrigerant in the system. Be a good neighbor. Know the laws and regulations, and make your own determination of the suitability and level of risk that you take in any alternative system. Again, the purpose of this document is to explore options and alternatives for the DIY auto AC mechanic. Feel free to share your experiences or additional research, but please be respectful.
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