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
Federal law does not require technicians to check for leaks or to repair
leaks prior to recharging an A/C system that is low on refrigerant.
California and Florida did require leak checks, but the laws have been
repealed. Wisconsin does not allow a system that is known to be leaking to
be recharged without first being repaired, but there is no requirement to
check for leaks. Even so, common sense should tell you it's always a good
idea to check for leaks - and to repair any leaks that might be found to
prevent the refrigerant from escaping again.
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
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
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
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
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.