MACS Show: Technical Session Coverage – UnderhoodService

MACS Show: Technical Session Coverage

Once a year, the Mobile Air Conditioning Society (MACS) hosts a trade show for A/C shop owners and technicians. This year’s event in Orlando, FL, provided a wealth of service information to those who attended the technical sessions. For those who couldn’t be there, we pass along some of the highlights from the technical sessions.

The good news is A/C service is booming and retrofits are still hot. According to a survey of MACS members, approximately 40% of the A/C work that’s currently being performed is on older vehicles with R-12 A/C systems. The rest are newer vehicles with R-134a A/C systems (50%) or older vehicles that have been retrofitted to R-134a (7%). Only about 3% of the vehicles serviced contain an alternative refrigerant.

Another finding in the MACS survey was that about 9% of the older vehicles with R-12 were retrofitted this past year to R-134a when they were serviced. The good news is there continues to be a need for retrofit parts and equipment. A/C systems are usually retrofitted when major repairs such as replacing a compressor, evaporator or condenser are needed.

The average A/C repair job, according to MACS, was $504 for all types of service work, and an average of $176 over and above any other repair costs to do a retrofit. The average mileage on all vehicles that were serviced in 2003 was more than 100,000 miles. That means that the owners of older vehicles are still putting money into their A/C systems, as the MACS survey also found, and that people are spending upward of $1,000 or more to repair and retrofit older cars and trucks.

Here’s more interesting information from the survey. These are the parts most often replaced when A/C systems are serviced: 17% – Compressor due to case leakage; 14% – Compressor due to internal failure; 10% – Leaky hose; 8% – O-rings or seals; 6% – Compressor clutches; 5% – Condenser; and 4% – Evaporators.

Another interesting finding of the MACS survey is that one out of four vehicles serviced ends up having the A/C system flushed either because the vehicle experienced a compressor failure or the system was found to be contaminated with sludge or debris. Most shops (92%) say they use liquid refrigerant to clean the A/C system, while 5% reported using an approved flushing chemical.

Flushing may be recommended for several reasons. One is to remove sludge from a contaminated system. Another is to remove debris following a catastrophic compressor failure. Flushing can also be used to remove excess oil from the system. Approved flushing chemicals include liquid R-12 or R-134a refrigerant, or any of several products made by various companies.

One new product introduced at the show was Honeywell’s new “Genesolv S Series” flushing agent. Based on HFC-245a, Honeywell says it has a faster drying time than other flushes currently on the market, and is safe, non-toxic and non-flammable. Honeywell recommends using a flushing chemical because it has a stronger solvent action than refrigerant alone and provides more effective cleaning.

The issue of flushing is still being debated by vehicle manufacturers. Some domestic vehicle manufacturers say flushing is okay. Other vehicle manufacturers, such as Toyota, say “no way.” SAE is currently developing a new standard for flushing chemicals to ensure materials compatability and suitability with today’s A/C systems.

To help clear up any misunderstandings technicians might have about flushing procedures, ACDelco announced a new “A/C Flushing” video (SD-AC-1.01-SUP) that is available through its distributors. One caution is that flushing will not remove all the metallic debris from a contaminated system. That’s why an in-line filter should be installed in the liquid line to trap any residual debris that a flush may have missed. ACDelco’s new universal in-line filter, p/n 15-10413, is smaller and easier to install than previous filters, uses green HBNR seals and fits several line sizes including 5/16-inch lines.

Visteon only recommends the use of solvent flushes by RTI and Bright Solutions in a closed-loop flushing process. These flushing machines use filters to keep contaminants from re-entering the system once they’ve been removed, and to remove air and moisture. Visteon says flushing with refrigerant alone is only effective for removing oil and doesn’t work very well for removing contaminants. The company also doesn’t recommend using a flush gun with shop air because the air usually contains humidity and oil vapor – two things you don’t want to introduce back into an A/C system. In addition, Visteon doesn’t recommend flushing hose with mufflers or expansion devices. These parts should be replaced.

According to DENSO Technical Services, flushing with refrigerant only is acceptable. DENSO does not recommend using any other chemicals for this purpose.

Leak detection dyes can be a godsend when it comes to locating hard-to-find leaks. Ultraviolet dyes can make even the smallest leaks clearly visible. But not everybody approves of their use. During the OEM panel discussion, representatives from the various automakers were asked for their recommendations regarding the use of leak-detection dyes.

Vehicle manufacturers who currently use dyes or endorse their use to find leaks include all three domestic vehicle manufacturers (Ford, GM and DaimlerChrysler), plus Nissan. Vehicle manufacturers who do not use or endorse dyes include Honda, Mazda, Toyota, Hyundai and Mercedes-Benz. OEMs that do not use or endorse dye may not honor a compressor warranty if it fails and is found to be loaded with dye.

Overuse of dye was the main concern that was voiced at the MACS show. Too much dye can dilute the compressor lubricant and increase the risk of compressor noise and failure. The standard recommended dose is only one-quarter ounce! A second dose won’t usually cause problems, but multiple doses over a period of time can overload the system with dye.

If you’re charging a vehicle with refrigerant that already contains dye, the refrigerant should be fed into the system as a liquid, otherwise you may not get enough dye into the vehicle to find the leaks.

In recent years, various sealer products have been introduced to stop refrigerant leaks. Some are activated by exposure to moisture, while others stop leaks by causing seals and O-rings to swell. These products are sometimes used to seal evaporator pinholes and other leaks when a customer can’t afford to have parts replaced. The labor to change an evaporator on some vehicles can be eight to 12 hours, or more, depending on the evaporator’s location and how much disassembly is required to extract it.

One thing all the members of the OEM panel agreed upon was that none approved the use of sealers. Toyota said the only thing they approve in their systems is refrigerant and the specified compressor lubricant – nothing else.

Technicians have voiced concern over the use of sealants because it can gum up their recovery and recycling equipment, service hoses and test gauges. To address this issue, several companies have introduced filters designed to protect service equipment from sealers and dyes. AirSept unveiled its new “Recycle Guard” sealant, dye and lubricant separator at the trade show. The unit features two porosity filters to trap debris, and a hollow “distillation” chamber that allows only vapor refrigerant to pass through the unit.

Nobody knows how refrigeration systems will change in the future, but it appears likely that R-134a’s days are numbered. The Europeans are seriously considering phasing it out starting in 2009. If that happens, the North American OEMs may follow suit.

Though R-134a poses no danger to the ozone layer if it escapes into the atmosphere, it is a “greenhouse gas” with a fairly high global warming potential of 1,300 (compared to 1 for carbon dioxide, which is nature’s own greenhouse gas). A leak that allows only an ounce or two of R-134a to escape into the atmosphere may not seem like a big deal but, over time, it all adds up, especially when you multiply small leaks times the hundreds of millions of vehicles that now share planet Earth with humanity.

The Europeans want future A/C systems to be as environmentally benign as possible. That means no chlorine-containing CFCs that cause ozone depletion and as little greenhouse gas effect as possible to reduce global warming. The new refrigerant must also be nontoxic and safe – though that doesn’t necessarily mean nonflammable.

The leading contenders that may eventually replace R-134a are plain ol’ carbon dioxide or a close cousin to R-134a called HFC-152a. Either substance will work as a refrigerant but both have some drawbacks. CO2 requires extremely high operating pressures (up to 1,800 psi on the high side, and 350 to 400 psi on the low side – compared to 300 to 400 psi on the high side for R-134a). The reason the pressures are so high is because CO2 doesn’t condense in the refrigeration circuit. It remains in the gaseous state. Consequently, the front heat exchanger is called a “cooler” rather than a condenser.

CO2’s main attribute is that it has virtually no impact on global warming or ozone depletion. CO2 is also nontoxic in small doses but concentrations over 5% can be lethal. It’s also cheap (about $10 for a 20-pound cylinder) and nonflammable. A number of test vehicles are running with CO2 A/C systems and cooling performance seems to be comparable to R-134a. SAE is still working on service fittings, and leak detection presents a challenge because natural levels of CO2 in the atmosphere may be higher than the amount emitted by a leak. Some type of ultrasound or infrared equipment may be required to find leaks, but dyes or plain old soap bubbles may also work.

HFC-152a, on the other hand, is almost a straight drop-in substitute for R-134a. The molecule is similar to R-134a except that two hydrogen atoms are substituted for two fluorine atoms. It has similar operating characteristics to R-134a but cools even better. One test in an otherwise unmodified Saturn Ion found that A/C duct outlet temperatures were several degrees Celsius lower with HFC-152a. Fuel efficiency was also up 10% at idle, and 20% at highway speeds. The system typically requires only about two-thirds of the normal charge with HFC-152a and can be used with current desiccants.

An environmental benefit of HFC-152a is that it has a global warming rating of 120, which is 10 times less than R-134a – but still a lot higher than CO2. That’s why HFC-152a is currently used in many aerosol products as a propellant. Its main drawback is that it is slightly flammable (Class 2A), but it’s not as flammable as propane or most other hydrocarbon-based refrigerants.

The first mobile A/C system to use HFC-152a was unveiled at the MACS show, a self-contained unit for off-road construction equipment that featured an oil-driven compressor. Made by Red Dot, the unit may be the forerunner of future HFC-152a A/C systems to come. If the Europeans force the auto makers to go to CO2, it will require a major redesign of existing A/C system components, as well as all-new service procedures and equipment. If they opt for HFC-152a, it may require adding special safety valves to vent refrigerant away from the passenger compartment in the event of a leak or accident, or using a “secondary loop” cooling system that eliminates the evaporator and substitutes a pair of heat exchangers to circulate chilled water into the passenger compartment. Either way, it will create more parts and service opportunities for the aftermarket.

  • Spring-lock couplings finally going bye-bye? Automakers love spring-lock couplings because they allow fast, easy assembly of A/C lines at the factory. But the couplings are notorious for leaking refrigerant. The next generation of “enhanced” R-134a A/C systems must have lower leakage rates, so SAE is developing new coupling standards that require a tighter seal. The goal is to reduce total refrigerant leaked for the entire A/C system to no more than 40 grams per year. That’s only 2 grams per joint per year if the system has 10 connections. The lower leakage levels will also require a new generation of even more sensitive leak detectors as well.
  • 42-volt systems and electric compressors. They’ve been talking about it for years, and it looks as if we’ll finally see 42-volt electrical systems in production soon. When they do arrive, look for a whole new generation of A/C systems with electric-driven compressors rather than belt-driven compressors. Toyota already uses an electric compressor in the Prius hybrid car to keep the A/C system working while the engine shuts off momentarily at stop lights to save fuel.
  • Charging accuracy. Because the A/C systems in many cars today require such a small charge (1-1/2 to 2 lbs.), it’s very important to make sure the system is accurately charged with the correct amount of refrigerant. Charging equipment with long hoses may contain 4 to 6 oz. of refrigerant in the hose. If this extra amount is not taken into account, you may end up overcharging the system.
  • Inadequate evacuation. Air and moisture contamination are leading causes of A/C problems. One of the reasons why is that many technicians do not vacuum-purge vehicles long enough to remove most of these contaminants. The vacuum cycle during normal refrigerant recovery is only about five minutes, which is not long enough to remove all of the air and moisture.

    Most experts say it takes 29.7 inches or more of vacuum for 45 to 60 minutes to adequately purge the system, 60 to 90 minutes for dual (front/rear) A/C systems, and up to two hours to purge a contaminated system in a colder or humid climate. The accumulator or receiver drier should also be changed if the system has been open or without a charge for a long period of time.

    Another suggestion: If air contamination has been causing noise or other problems, deep vacuum-purge the system and recharge it with virgin refrigerant rather than recycled refrigerant. Why? Because recycled refrigerant may contain 2 to 3% air.

  • Premature heater core failures. Some vehicles have had problems with premature failure of heater cores. Causes include manufacturing defects (an estimated 2%); corrosion due to dirty, contaminated coolant; and corrosion due to electrolysis. If you find black residue inside the heater core, it indicates electrolysis (check for loose or missing ground straps between the engine and body). Either way, the coolant needs to be changed and the system needs to be thoroughly cleaned and flushed before it is refilled. The system may have to be flushed several times if corrosion is severe. It’s also important to get all of the air out of the system. Some cars have restrictors in a heater hose to slow coolant flow. If a hose is replaced and the restrictor is left out, the coolant may rush through the heater too quickly and erode the core.
  • Quick fix. Here’s a fast way to see if a sticking blend air door inside an HVAC unit is causing a heating or cooling problem. Pinch one of the heater hoses shut to see if A/C outlet temperature drops. If it drops, blend air is leaking heat from the heater core into A/C air flow.

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