Refrigerant leaks are the number one cause of poor A/C cooling performance. The amount of refrigerant in an A/C system is critical for proper cooling. Any loss of refrigerant reduces the system's ability to transfer heat, causing the compressor to work harder and the system to cool less efficiently. To make matters worse, the refrigerant capacities of most late-model passenger car A/C systems have been lowered to reduce emissions. The typical A/C system today only holds about 24 oz. of refrigerant, and some newer Saturn models are down to a mere 13 oz!

With these facts in mind, it should be obvious that finding and fixing refrigerant leaks is more important than ever before. That's why technicians need detection equipment that can help them find even the smallest leaks.

Leaks occur most often at the compressor shaft seal, and at hose and pipe connections where O-rings and seals are located. High and low pressure refrigerant hoses, can also leak, as can the condenser and evaporator (most often from internal corrosion). Large refrigerant leaks, like the kind that can discharge an A/C system within a few weeks or months, often leave telltale greasy stains that indicate the point of leakage. But this is more the case with older vehicles (those built prior to 1994-'95) that have R-12 A/C systems and use mineral oil to lubricate the compressor. On newer vehicles with R-134a systems, PAG oil lubricants leave fewer obvious clues where there's a leak. And with small leaks, there may not be any visible clues at all. That's where leak detection dyes and electronic leak detectors come in handy.

Leak Detection Dye 
Fluorescent leak detection dye that is added to refrigerant will typically glow a greenish-yellow or greenish-blue when illuminated with an ultraviolet (UV) light (also called a "black light" because of its purplish glow). As the dye circulates throughout the system, it will follow the refrigerant through any pinholes or cracks if there are any leaks. You can then examine the hoses, connections and various parts of the A/C system with an ultraviolet light to see if there are any telltale traces of dye on the outside of these parts.

One of the benefits of using leak detection dye is that it stays in the A/C system as long as the system contains refrigerant. Some vehicle manufacturers now add dye at the factory when they initially charge the A/C system so technicians can find any leaks that might occur. Many shops also add dye as "insurance" to make sure a system isn't leaking after it has been serviced - and to encourage customers to bring back their vehicles for future leak inspections.

Dye can be added to an A/C system with the refrigerant (pre-mixed), or injected using a cartridge and squeeze-handle injector gun through the low-side service fitting. A single shot of dye is typically 1/4 oz. (7.5 ml).

Shining a Light on the Subject
To illuminate the dye, an ultraviolet light source is needed. UV lights are available in a wide variety of sizes and styles, ranging from large 12-volt DC and 110-volt AC models to small flashlights. A large spotlight-sized lamp is good for illuminating a wide area in the engine compartment while a smaller, more focused light is better for hard-to-reach areas and working in tight spaces. Donning a pair of yellow-tinted glasses also improves visibility by increasing the visual contrast of the dye.

The latest trend in dye detection lights is a new breed of UV lamps that use LED lamps instead of traditional incandescent filaments. LEDs are very long lived (up to 10,000 hours or more) and use much less current than traditional lamps. The light can also be sharply focused to pinpoint leaks in tight areas. Such lamps typically use 5 to 7 LEDs to illuminate the dye.

As effective as dye is, it does have a few limitations. One is that it's hard to see leaks in "hidden" areas such as a leaky evaporator inside the HVAC case. If you suspect an evaporator leak and dye has been added to the A/C system, you can check the evaporator case drain hose to see if any dye has gotten that far. The alternative is to spend several hours tearing apart the dash and HVAC system to visually inspect the evaporator for leaks. Or, you could check the evaporator for leaks by simply inserting the probe of an electronic leak detector into the HVAC case.

Dye also needs time to work. Once it has been added to an A/C system, it needs time to circulate with the refrigerant. It may take several hours or even several days of operation before enough dye leaks through a crack or hole to reveal a leak.

There is also a risk of using too much dye. Though leak detection dye is compatible with refrigerants and compressor lubricants, adding several successive doses of dye in an attempt to find a leak may increase the risk of plugging an orifice tube or reducing the lubricity of the compressor oil. If someone has already added dye to the system, don't add more. It only takes a small amount to reveal a leak, and adding more won't speed up the process or make it any more effective.

Electronic Leak Detectors 
Another tool that can help you find refrigerant leaks is an electronic leak detector. There are three basic types:

1. Electromechanical corona discharge detectors. This type of detector pulls air through an electrical field around a wire. The presence of refrigerant or other gases in the air changes the current in the wire to trigger an alarm. The tool may beep or flash when a leak is detected. The level of sensitivity for this type of tool is not as high as the next two technologies, but it can still find leaks as small as 0.3 oz. to 0.6 oz. per year. The Society of Automotive Engineers (SAE) J1627 specification calls for a minimum sensitivity of leaks on the order of 0.5 oz. per year.

2. Solid-state heated diode detectors. The sensing element in this type of detector is a heated ceramic diode. When air containing a halogen gas is drawn across the diode, it generates an electrical signal that triggers the alarm. This type of equipment is much more sensitive than the corona discharge detectors, and is capable of finding leaks as small as 0.1 oz. a year with R-134a. It also gives fewer "false alarms" because it only reacts to halogen gases (refrigerants) and not other fumes that may be present under the hood of a vehicle. But its drawback is sensor life. The heated diode sensor can be contaminated with moisture and typically lasts only two to three years in a busy shop environment. The sensor can be replaced for an average cost of $20 to $40.

3. Nondispersive infrared detectors. This is the newest leak detection technology and will be used in more new leak detectors. This type of equipment uses an "optical bench" that shines an infrared light of a specific wavelength through air passing across the bench. If the air contains any halogen gas. The gas disrupts the light beam and triggers an alarm. It's the same basic technology that is used in many refrigerant identifiers to find out what kind of gases are inside an A/C system.

The main advantage of nondispersive infrared technology is that its sensitivity is on par with heated diode detectors (down to 0.1 oz./year), but it doesn't have contamination issues or a limited sensor life. According to one manufacturer of A/C diagnostic equipment, the projected service life of the infrared sensor is up to 15 years or more - after that, who cares because there will be another new technology to replace it.

Down the Road
SAE is working with the vehicle manufacturers and the Mobile Air Conditioning Society (MACS) to develop "enhanced," next-generation R-134a systems that are smaller, more energy efficient and tighter than today's A/C systems. The program is called "I-MAC," which stands for Improved Mobile Air Conditioning. One of the program's goals is to reduce refrigerant leakage 50% compared to current A/C systems. This will require the use of improved seal designs, hoses and O-ring connections - and even better leak detection equipment.

When SAE revises its current J1627 standard, next-generation electronic leak detectors will probably be required to detect leaks as small as 4 grams/year (compared to 13 grams/year now). Consequently, a leak detector you buy today may or may not be sensitive enough a few years down the road to find leaks in future cars.

Another uncertainty that may impact future A/C leak detection equipment is whether or not R-134a will be phased out and replaced by yet another alternative refrigerant. The change to R-134a was made to address the ozone problem. It contains no ozone-damaging fluorocarbons, but it is a greenhouse gas that contributes to global warming. R-134a has 1,300 times the global warming potential of carbon dioxide (CO2), so if automakers are forced to switch to a more environmentally friendly refrigerant such as CO2 or HFC-152a it will require a whole new generation of service and leak detection equipment. But, that may not happen for another decade or so.