The Tiniest Mistake

Is faulty HVAC diagnosis costing you money in the cold of winter?

"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."

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