Risk versus Reward

When the half-century reign of chloro-fluorocarbon refrigerants like R-12 came to an end over a decade ago, a major threat to Earth’s essential ozone layer seemed to be removed. The switch to R-134a promised an environmentally sensitive way to keep residential, commercial and mobile refrigeration going for years to come. Few could have predicted that global warming would emerge as an environmental threat at least as great as ozone depletion and that hydro fluorocarbon refrigerants like R-134a would have to go, like R-12 before it. Today the need to replace R-134a is acute and much research is going into substitutes like carbon dioxide and alternates like R-152a.

But with the phase-out of R-134a, what about the existing vehicle fleet? One service option is the current family of hydrocarbon refrigerants. Based on proprietary blends of isobutane and propane, HC refrigerants offer fast pull down times, low vent temperatures and low head pressures in unmodified stock mobile A/C systems. The primary issue for detractors of hydrocarbons is that they’re flammable. Addressing the flammability issue is key to both consumer and OEM acceptance of both hydrocarbon and difluoroethane-based refrigerants like the current frontrunner in the OEM search, R-152a.

What about performance? Current hydrocarbon users report excellent system performance as a drop-in replacement and several studies confirm that hydrocarbons and R-152a can work well as a drop-in replacement for R-134a. An example is the extensive technical analysis published by Delphi’s Mahmoud Ghodbane in SAE Technical Paper 1999-01-0874. That study concluded that system performance and global warming potential were addressed well by both HC and R-152a technologies, suggesting that the flammability risk could be addressed by OEM’s by using a secondary loop where the A/C system would chill a coolant/water mix much like current antifreeze solutions. That chilled water would be circulated through the passenger compartment. The study also contrasts the willingness of European refrigeration manufacturers to embrace flammable refrigerants with U.S.-based OEMs concern about liability issues.

Another technology currently under review by OEM’s are dump valves that would rapidly depressurize the system in the event of a leak by blowing it overboard, perhaps into the wheel well area.

That’s fine for the future, but what about the current vehicle fleet? Fire risk in existing systems using hydrocarbon refrigerants is a common concern, but how realistic is it?

Andrew Kusmierz, research engineer for Safety Consulting Engineers Inc. is a member of the flammability subcommittee of the ASRAE (American Society of Heating Refrigeration and Air-Conditioning Engineers) committee for the designation and safety classification of refrigerants: “For a lot of people on the street there’s a psychological barrier to the use of flammable refrigerants. I’ve seen discussion groups on the Internet that describe leaking refrigerant igniting from broken headlamps and flashing back to ignite condensers. It’s just not true. If you understand the combustion process, it can’t happen. You need a mixture of flammable gas and air in a certain proportion and you need an ignition source. If it happens in a moving car, properties like wind and speed influence the process. If a pinhole mixes flammable refrigerant with air you might have a flammable zone, roughly from 2 to 10 percent gas. If ignited by a match, it might burn in that zone, but it can’t burn in the condenser or evaporator. The public’s image of that explosion isn’t correct.”

Several manufacturers have shown demo tape of violent explosions in simulations of evaporator leaks when using hydrocarbon refrigerants, but Kusmierz is unconvinced.

“I’ve heard of tests where cans of refrigerant were released into the car interior and ignited. If it’s mixed and recirculated, after several tries it will explode. What is the chance of a fire happening in real life? Most of the A/C system joints are under the hood, including the evaporator. The chance of leaking the whole charge into the passenger compartment is unlikely. Reaching the lower flammability limit for the gas also depends on the cabin volume and on the natural air exchange in the cabin.

We’ve studied R-152a and performed a risk analysis including ignition sources and leak rates, and the risk factor added is 10-7, which is almost impossibility. With the amount of refrigerant charge in a car, you’d have to discharge everything into the cabin without any loss. Then you’d be lucky to ignite it. The worst situation would be a crash, but it’s hard to find significant numbers about fire causes, because there are twenty gallons of gasoline involved. You need a huge displacement of the dashboard to release refrigerant. Then you’d certainly have windows broken. There’s a lot of confusion about this issue. You have a continuous gas supply to your home with a single shutoff and maybe 600 grams in your car. The amount of refrigerant in the system is important. A few hundred grams in a car isn’t a risk, but in an industrial application that might require 500 pounds, we require a risk assessment.”

Kusmierz notes that a rapid release of conventional refrigerants can form aerosols with flammable lubricants, also creating a flammability issue.

Using Hydrocarbons

Installing hydrocarbon refrigerants are not difficult. Conventional charging techniques work, although lower head pressures can be expected. Conversion charts for refrigerant charge are available from the manufacturers, and no special adapter or valving is needed. For leak detection, most hydrocarbon products use a scent such as pine and some also contain a leak detecting dye. Lubricants should remain as they were in the original system, R-12 or R-134a. Hydrocarbons should be recovered into a separate container.

What about safety during service procedures? As a flammable gas, the same sort of safety procedures should be followed as would be used for fuel injection service. Smoking and open flames are out and adequate ventilation should be provided. Toxicity of hydrocarbon gases are low and with the added odourants, it’s unlikely that leaks will be a contact or inhalation risk.

While all HC manufacturers declare complete compatibility with existing systems, most parts manufacturers don’t, so it’s a good idea to determine if warranties will be affected by using hydrocarbons. Many manufacturers offer supplementary guarantees that the gas won’t harm system components, however, and there are HC-warranted parts available in Canada, such as the compressor line available through Duracool.

Technically, there are benefits of hydrocarbons over R-134a. According to Red Tek’s Gene Brewer, “it’s easier on the A/C system components and can offer up to 40 percent lower head pressures. There are also some savings possible in terms of improved fuel mileage.”

Major auto makers are wary of possible litigation surrounding the use of flammable refrigerant gases. As a business, are you at risk using hydrocarbon refrigerants?

Deep Freeze Refrigerants’ (Duracool brand) Larry Parkinson states unequivocally, “We’ve never had an incident or issue of any kind in the years that we’ve been supplying Duracool to the Canadian aftermarket. Duracool has been installed in thousands of cars and light trucks with no problems at all.”

Gene Brewer, president of Red Tek (Red Tek brand) reports a similar experience. “We’ve been in the business since 1998” he declares, adding, “We estimate that we have over 500,000 vehicles running on Red Tek. We’ve had zero issues.”

None of the manufacturers contacted reported any difficulties in obtaining insurance for HC sales and none reported making a claim.

If hydrocarbons work well, are cost effective and are safe for general automotive use, will they eventually break through into the OEM ranks? Bob Small, general manager for HC Refrigerant Products (HC-12a brand) thinks so. “It’s like aftermarket parts years ago. If you didn’t buy
OEM parts, your warranty was void. R-134a has been the industry standard, but that’s changing with the Kyoto Accord. HFC’s are being phased out everywhere and R-134a prices are going to go up considerably. They’re going to replace it with R-152a. The stigma with hydrocarbons has been flammability, but if you check R-152a, it’s a highly flammable refrigerant.”

If R-152a does become the new standard, the aftermarket will get used to working with flammable refrigerants on a daily basis, possibly opening the door for widespread use of hydrocarbons as drop in replacements without the current stigma. According to the HC supplier community, it will happen. Bob Small’s reaction is typical: “it’s just a matter of time. Whether its five years from now or ten years from now, it’s going to happen.”

What do those numbers mean?

The number codes for refrigerants are not arbitrary; they reveal lots about the composition of each molecule of refrigerant. To determine what’s inside a pure fluorocarbon refrigerant, for example, add 90 to the product number. For R-134a this would be:

90 + 134 = 224

The first digit, 2 represents the number of carbon atoms in each molecule

The second digit, also 2, represents the number of hydrogen atoms

The third digit, 4 is the number of fluorine atoms.

Want to know if it’s a CFC (chlorofluorocarbon)? Multiply the first digit by two, subtract the second and third digits, then add two to the result. The resulting number is the number of chlorine atoms. For R-12a, it’s 2. For R-134a, it’s 0, which is why R-134a is an HFC (hydrofluorocarbon), not a CFC.