The Tiniest Mistake

Sometimes the tiniest mistake can be very costly. Take the heating, ventilation & air conditioning (HVAC) system: like the tires or the brake lines, it's one of the systems on a vehicle where a flaw no bigger than a pin prick, gone unnoticed, can cause utter disaster.

Paul DeGuiseppi, manager of service training for the Mobile Air Conditioning Society (MACS), has seen a lot of tiny mistakes become major problems in his day.

"Technicians are making mistakes--we even have a published list of the top 11 mistakes they make--and it's because of a lack of knowledge and lack of training," he says. "There's this attitude of 'That's the way we've been doing it for years,' and that's the main thing I see. Other things I hear: 'It worked on my '82 Monte Carlo...' 'That's what the salesman told me would work...' 'The label on this container says...' All those kinds of things."

It's enough to make a professional trainer pull his hair out. But, because every technician who works with refrigerant is required by the Environmental Protection Agency (EPA) to be certified, DeGuiseppi keeps on hammering home his message, in class after class.


Of course it makes perfect sense to talk to an expert about air conditioning when winter is approaching.

"Based on the fact that you're using your air conditioning for window defrosting, you should absolutely pay attention to it in the wintertime," DeGuiseppi says. "You also have to apply the same maintenance list to the cooling system. Cooling systems and A/C systems are very interrelated. The belt that spins the compressor is often the same belt that spins the water pump. The cooling fan that comes on when you turn the A/C on is the same cooling fan that comes on when the engine reaches a certain temperature. And of course, the cooling system is important in wintertime for heating purposes.

"Keep in mind that at around 35 or 38 degrees, the compressor will not engage anyway, and that's for two reasons," he explains. "One: they don't want the compressor operating at such low ambient temperatures, because that could damage the compressor, due to the fact that the oil is thicker, so it might not receive adequate lubrication. The second reason is, it's really not needed, because the colder the air is, the less humidity it contains, but when the compressor runs it dehumidifies the air, and the dehumidified air just does a better job of clearing the windshield.

"A diagnostic process that many technicians will use is, if they have a lack of compressor clutch engagement, the first thing they'll do is turn the controls to defrost," he explains. "If the compressor does not engage, they know they need to start digging."

Unfortunately, many technicians don't know where to start digging, because their training isn't up to snuff, according to DeGuiseppi.

What's missing?

"Basically, not staying current with things that are happening, or have been happening, with air conditioning," DeGuiseppi says, "like smaller charge systems, understanding why it's so important to recharge with incredible accuracy, maintaining the equipment to help you do this the right way.

"A lot of people don't understand this: many old systems held three pounds of refrigerant; some today hold less than a pound," he explains. "You have to be much more accurate on these tighter systems, because the tiniest mistake can cause it to blow too warm or damage the compressor or many other things. But basically, repeat compressor failures, when they're swapping out compressors and other components, means they're not doing the full job, not doing the job the right way."


"The biggest issue is leaks," says William Johnston, climate control manufacturing & service manager for Ford Motor Company. "We struggle with the technician's ability to properly identify a leak. In response to that, the SAE has recently developed new standards for leak detection tools and refrigerant recovery/recycling machines.

"Those new standards have tightened up the accuracy of these machines," he says. "For example, the refrigerant recovery machines; with these new standards they are capable of recovering 95 percent of the refrigerant to an accuracy of plus or minus one ounce within 30 minutes. Some of the older machines were in the ballpark of half a pound or more accuracy, so you couldn't use that as a diagnostic tool. By fleets upgrading to these new machines, they can use that as a mode of diagnosis to say, 'Hey, this car is really low on refrigerant, so maybe there's a leak somewhere that we can go after.'"

SAE has also developed a new standard to increase the sensitivity of electronic sniffers that technicians can use to detect leaks. "But that standard was just released," Johnston says, "and I think there's only one tool on the market that meets the new standard. But a flood of them will be coming out later this fall."

Relying on the standard black light and goggles technique is, Johnston admits, less than perfect. "Having an electronic tool or other means to measure the refrigerant in the car can be a big help," he says.

"There are new federal regulations coming into play in the next year or two that make us responsible to create vehicles with much, much smaller leak rates," Johnston says. "And to find these leaks--we're talking in parts-per-million resolution--you need to detect a refrigerant atom in the atmosphere around the joints or around any part of the A/C system, that sensitivity of the tool really needs to improve, which is happening.

"Sometimes a part can only leak when it's dynamic, when the vehicle is moving," he explains. "So finding a leak is next to impossible; finding a leak on a compressor or a joint when the vehicle is stationary, you might not find anything."

But it's not just the feds that have Johnston and his colleagues striving for greater accuracy. New laws are "coming from all over," he says. "The State of Minnesota is going to require us to publish what our leak rate is per vehicle, and California is hinting at things they want to do."


While most consumers don't notice problems with their HVAC systems until the spring and summer months, Johnston advises fleets to conduct regular inspections regardless of the season to catch problems before they cause major trouble.

"You'd probably want to look at the system every 50,000 miles in detail, to really determine if the A/C is pulling the temperature down like you'd expect in a hot environment," he says. "You know, sniff it for leaks, look for evidence of leaks involving dye or oil, leaking around some of the joints or the compressor. At maybe 75,000 miles actually evacuate the system with one of the newer machines, measure how much is in there, and then recharge it."

According to Johnston, R134a refrigerant doesn't lose its effectiveness over time. The material will last forever inside the closed-loop A/C system as long as it's never exposed to the outside environment.

"If it's leaking, you'll lose some amount of refrigerant," he explains. "The A/C system has a peak performance amount of refrigerant; we do a lot of tests to determine what that amount is on a vehicle. If you have a vehicle that's at 25 ounces as its peak performance, it may leak very slowly, and at 50,000 miles you may be down to 20 ounces of refrigerant. It's not going to perform as well at 20 ounces. If it's a really hot, humid day out there, the customer's going to notice that five ounce degradation in refrigerant level."

Of course, in a cold winter climate, even with the windshield defroster on, the driver may not notice any difference until the damage is done.

"If there's a leak, as you lose charge, there's less refrigerant, which means there's less oil being circulated," Johnston says. "The compressor starts to heat up, and it develops more friction. Eventually, given a low enough refrigerant level, and low enough oil in circulation, you have a failure of the compressor."


If your technicians ever need to replace refrigerant or oil in an HVAC system, MACS' DeGuiseppi has one simple rule for them to remember: Always follow the OE's recommendations concerning tools, equipment and chemicals.

"Vehicle manufacturers approve only two refrigerants," he says. "That's all there is. There is no other approved refrigerant besides R134a that is approved for use in 134a systems. It is still acceptable according to all the automobile manufacturers to use R12 in the old air conditioning systems that were designed to use it. Or, if a manufacturer has a retrofit recommendation, the only refrigerant they recommend is R134a. There is no other refrigerant that any vehicle or system manufacturer endorses."

Want to make a quick $10,000? DeGuiseppi makes a standing bet with all his students that if they can find a light-duty car or truck that has ever left an assembly plant with any kind of oil in its R134a A/C system other than polyalkylene glycol, or PAG, he will fork over ten grand.

"Since the beginning of R134a, there's been no other kind of oil recommended for use in production R134a systems by an OE vehicle manufacturer other than PAG," he says. "But of course there are other types of lubricants on the market that some people insist on using. This is the biggest mistake out there."


Retrofitting an R12 system to R134a? In 99 percent of retrofits, DeGuiseppi says, PAG is the recommended oil.

"But, there are a few vehicles--a scant few--that do recommend another type of oil called ester, or polyol ester, and in those cases those are the ones you should use," he says.

"Back in the day, PAG was a lot more expensive than ester," he continues, "and for some reason it got into the psyche of many a technician that ester was the 'universal retrofit oil,' and there never has been such a thing."

DeGuiseppi adds that, although there are different types and viscosities of PAG oil that are recommended for different compressors, PAG is all your technicians should ever use.

MACS offers several classes that can keep your technicians up to snuff on what DeGuiseppi describes as "the pretty drastic changes that have taken place in A/C systems just in the last five years: smaller charges, smaller amounts of oil, different strategies for compressor clutch engagement.

"If it's been more than a couple of years since your technicians have taken a training class," he says, "get them one."

Even if it's in the dead of winter.

For information on MACS training classes, visit