MACS Monthly Newsletter - 2021 - OCT3

of forming gas leak detection, so the market for this equipment
hasn't really grown here.
ULTRASONIC DETECTORS
Ultrasonic leak detection has been around for a long time,
commonly used to find automobile leakage on body seams,
using shop air. However, very sensitive ultrasonic detectors
are available for refrigeration system leakage, and one
vehicle manufacturer-Honda-has specifically accepted it
for automotive A/C, with the system under vacuum. Those
who have tried it tell us that it seems to work at tracing larger
leaks. However, there are no ultrasonic detectors that have
ever been tested against SAE standards, so we can't compare
them directly to the J2791/J2913 units. One manufacturer
of ultrasonic claims detection of leaks as small as 40 grams/
year, but that's 10 times what our SAE certified units have
been demonstrated to find (4 g/yr), and what the industry has
decided is needed. In any case, we have no verifiable data on
how well it works in finding small-but-repairable refrigerant
leaks. v
Trace Dye Moves To The Forefront Again (With A Big If)
Because R-1234yf is so expensive, more and more car makers
are installing trace dye on the assembly line, with Toyota/
Lexus remaining a notable exception, recommending only
the use of an electronic leak detector specified for R-134a
(SAE J2791) and R-1234yf (SAE J2913).
Okay, most systems contain trace dye, but as we've noted
many times, newer compressors contain valves and flow circuits
that keep most oil in the compressor, minimizing circulation
through the refrigeration circuit. And trace dye works
by mixing with and circulating through the system with the
However, with dye factory-installed, there should be a dye
trace at any leak point by the time a leak occurs. But technicians
seem to be having a lot of trouble finding it. Why? The
Figure 3: This GM truck's grille and shutters obstruct access
for a leak detector probe to condenser fittings. Removal
of the grille, and opening the shutters is likely to
be necessary.
oil. Fortunately, even a 90% efficient compressor oil control
valve, over a period of time, allows enough oil/dye circulation
through the entire refrigeration system. And at higher
compressor rpm, the valve efficiency drops significantly, and
much of the dye-laden oil leaves the compressor and circulates
throughout.
But you should understand that late-model A/C systems
have oil capacities as low as 3-1/2 oz, versus the 5 to 8 oz of
not that long ago; and you may even remember systems with
OE fills of 11 oz. With reduced oil circulation throughout the
system, a result of keeping most of the oil in the compressor,
a lowered oil capacity is not surprising. So, although oil circulation
throughout a new car refrigeration system may not be
an issue, the time needed for a shop-added dose of trace dye
to mix with the oil and reach the needed location in a leaking
system may require some patience.
October 2021
3
Figure 4: Placing shower cap over compressor nose, immediately
after running the A/C, should allow refrigerant
vapor to accumulate under the cap if there's a significant
shaft seal leak. Allow time for vapor to escape shaft seal,
then push leak detector probe under cap to check. Note:
Be careful when using this method on a hot compressor.
Use a heat resistant shower cap (something heavy duty
so it won't melt).
primary reason, an OE service engineer told us, is that many
of the refrigerant system joints are buried in underhood locations
and it can take a lot of work to remove parts for access,
particularly at the front end cooling module. If there's a leak
at the condenser, a very common location, at the very least
you have to open the grille shutters (Figure 3), perhaps even
removing the grille first, to be able to slip in an ultraviolet light.
Fortunately, today there are many very bright-- as well as very
compact-- UV lights.
Of course, this also is true for electronic leak detector
probes, but they typically are a bit easier to work into position
throughout the refrigeration circuit. However, as that OE
service engineer pointed out, you have to be able to run the
leak detector probe over the entire refrigeration circuit, and
sorry, but that often isn't easy or fast. Remember, a 4 g/yr leak
is very small, but also keep in mind (1) there may be several
in the system; 2) with today's refrigerant charges of a pound
or less, it doesn't take very many leaks for the refrigerant loss
to add up to a significant amount (2-3 oz is 50-75 grams and
that amount of loss on a smaller system will result in a loss of
MACS Service Reports
GM
MACS Staff
MACS Monthly Newsletter - 2021

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