When a customer’s A/C system isn’t cooling well and the refrigerant charge is low, you know the system is leaking. The question is where? Finding refrigerant leaks on today’s vehicles can be a challenge. For one thing, many of the A/C system parts are buried and difficult to reach. Also, most systems today hold much less refrigerant than they did a decade ago. The typical refrigerant charge in most cars today is 24 oz. or less, and some are only 12 to 14 oz.! That leaves little reserve capacity for loss due to leakage. So you need leak detection equipment that can find even the smallest leaks.
Essentially, there are two methods of finding refrigerant leaks today: electronic leak detectors and fluorescent leak detection dye. Either method can be used by itself to pinpoint leaks, but the best results are often obtained by combining both methods — especially on late-model R-134a A/C systems with small charge capacities.
Shed Some (UV) Light on the Subject
In recent years, Ford, General Motors, Chrysler and Mazda have been adding leak detection dye to the factory refrigerant charge. This allows technicians to see leaks with an ultraviolet (UV) lamp (also called a “black lamp” because of its purple-colored light). The dye remains in the system and circulates with the refrigerant indefinitely or until a leak occurs. At that point, the dye seeps through the leak and leaves a telltale stain that glows greenish-yellow or greenish-blue when illuminated with a UV light source. With this approach, you can often find leaks as small as 1/8 oz. of refrigerant per year!
One of the reasons why dyes have become so popular is because they are easy and inexpensive to use. All you need is a bottle of dye (a single dose is typically 1/4 oz.) or refrigerant that has already had dye added to it. Dye can be added to an A/C system when it is topped off or recharged with refrigerant. The dye may be premixed with the refrigerant, or it can be injected into the system through the low-side service port with a special injector tool that resembles a small caulk gun. Some replacement accumulators and receiver/driers also contain a small wafer that releases tracer dye into the system once it has been recharged and is running.
Dye needs time to circulate through the system, so it is usually necessary to run the A/C system for several hours or to drive the vehicle for a couple of days before a small leak will reveal itself.
To find the leak, a UV lamp is used to scan all the places where leaks typically occur: the A/C compressor shaft seal, all hose and pipe connections, and the condenser. To enhance visibility, yellow-tinted goggles may also be worn to increase the color contrast between the dye and background.
The intensity of the UV light source is important because the brighter the light, the easier it is to see small patches of dye with normal indoor or outdoor lighting. Partially lowering the hood or turning off the lights in the service bay makes it easier to see the dye. Another trick is to use a fabric hood or shroud around the engine compartment to block out ambient light.
UV lamps range in size from large 12-volt DC or 110-volt AC models to small battery-powered flashlights. A large spotlight-sized lamp is good for illuminating a wide area in the engine compartment while a smaller, more focused beam of light is better for hard-to-reach areas and working in tight spaces. Some of the newer UV lamps use LEDs (Light Emitting Diodes) instead of a traditional filament-style bulb to create ultraviolet light. LEDs don’t have a filament so they won’t break if somebody drops the lamp. LEDs also use much less energy than ordinary bulbs, and last up to 10,000 hours.
So what are the drawbacks of using leak detection dye to find refrigerant leaks? The main drawback is that there is a risk of using too much dye and gumming up the A/C system. If one dose of dye fails to reveal a leak, two or three additional doses won’t make any difference. If a system already contains dye, do not add more.
One way to tell if the refrigerant already contains dye is to examine the area around both service fittings for telltale dye stains. If you see dye at either fitting, the system probably contains enough dye to reveal a leak. Go ahead and inspect the entire system for leaks. Even if the A/C system has lost most or all of its refrigerant, you should have no trouble finding the leak if the system contained dye.
One problem to watch out for here is dye stains left over from previous A/C repairs. If the system contained dye, was leaking and was repaired, there may still be residual dye left around the repair area (which is why you should clean off the dye after repairs have been made). If the customer failed to tell you the system had been repaired earlier, you might think the former repair is still leaking. The only way to know for sure is to clean off the old dye and see if any fresh dye reappears at the same point.
Something else to keep in mind when using dye is that it won’t necessarily tell you if a leak is large or small. In theory, the larger the stain, the larger the leak. But some leaks may be so small as to be almost insignificant. Remember, dye can reveal extremely small leaks. Consequently, you have to decide whether or not a leak is significant enough to need fixing.
Another limitation of relaying on dye alone to find leaks is that you usually can’t see the evaporator directly because of its location inside the HVAC unit. You can, however, use a UV lamp to check for traces of dye around the evaporator drain hole (assuming a leak is large enough for condensation to carry some dye with it to the drain hole). A better tool here would probably be an electronic leak detector.
Electronic Leak Detectors
There are three basic types of technologies used in electronic detectors: corona discharge, heated diode and infrared.
Corona discharge is older technology. Air is pulled through an electrical field around a wire. The presence of refrigerant or other gases in the air changes the current in the wire and triggers an alarm. Unfortunately, this technology can be fooled by other substances and is therefore vulnerable to false alarms. Also, it isn’t as sensitive as heated diode or infrared detectors. Corona discharge detectors typically can find leaks as small as 0.5 oz. per year.
Heated diode detectors use a heated ceramic diode that generates an electrical current when it comes into contact with halogen gas. This technology is more sensitive and can often detect leaks as small as 0.1 oz. per year, and it is less apt to give false alarms. The cost, though, is typically higher than that of corona discharge detectors. The sensing element is vulnerable to contamination and has a limited life, so it usually must be replaced after two to three years of normal use.
Infrared detectors use an “optical bench” that uses an infrared light beam to detect refrigerant. The gas disrupts the light beam and triggers the detector. It’s the same basic technology that is also used in many refrigerant identifiers to reveal what kind of gases are inside an A/C system. Infrared detectors are also very sensitive and can detect leaks down to 0.1 oz. per year. But it isn’t vulnerable to contamination and can last up to 15 years or more.
Refrigerants Premixed with UV Dye
Most shops use Recover/Recycle/Recharge (R/R/R) equipment to charge A/C systems. These units need to be preloaded with refrigerant; experts at UView Ultraviolet Systems were concerned that the dye would be separated from the refrigerant during this process, so they researched the effectiveness of using refrigerant mixed with UV dye when used with R/R/R equipment.
UView commissioned a third-party laboratory to conduct the tests with a leading manufacturer’s recover/recycle/ recharge unit. The refrigerant was removed from the 30-lb. cylinder in a liquid phase according to the manufacturer’s recommended operating procedure to load the on-board storage tank with refrigerant.
Samples were taken from the R/R/R machine’s on-board storage tank and the oil separator. These samples were compared with a sample from the refrigerant manufacturer’s 30-lb. cylinder mixed with UV dye.
The results showed that 95% of the dye was removed by the oil separator on R/R/R machine. Therefore, if a technician were to recharge an A/C system with the R/R/R machine, there would not be enough dye in the refrigerant to detect any leaks and additional dye would have to be added to the A/C system.
Avoid Damage to A/C Systems
Some dyes are formulated with a solvent called Aromatic 200. If too much of this solvent is added to an A/C system, the lubricating properties of the system’s oil are changed and would be adversely affected. In addition, the solvent itself is not miscible in R-134a. The potential for damage due to this is not yet known. The solvent also contains naphthalene, which is listed by OSHA as a hazardous material.
Look for dyes that are processed with A/C-grade lubricants, it’s important to use a product that is safe for your equipment and your personnel in any dosage.