MACS Monthly Newsletter - 2020 - AUG2

Tracer Products

high a speed as is reasonably feasible, because
oil separators are less efficient under those conditions, so more oil will
circulate with the refrigerant.
However, many car
makers (Toyota/Lexus
the long-time exception)
install trace dye on the assembly line, often in the
form of a wafer in the receiver-dryer/modulator
(Figure 2). So, it should
be well circulated and at
the leak site by the time
a leak occurs. Perhaps a
bigger issue is that many
leaks are at rub-throughs,
which may be hidden
from easy view. You may
have to remove an underhood part to be able
to follow the refrigerant
Figure 2: Trace dye wafer in receivline circuit completely.
er-dryer, installed on car assembly
What to think if no leak
line, takes just minutes to dissolve
shows up? There are sevand the dye to circulate with refrigeral possibilities: Leakeration oil.
age from the compressor
shaft seal, the under-dash
evaporator, and a very small leak elsewhere, but from which the
oiled-dye didn't escape.
The truth, however, is that most leaks a technician can't find
are in places he didn't look closely enough. Pinholes in condenser tubing, much of which isn't easily accessible, are an example.
The cap plug (for the receiver-dryer cylinder built onto the end
of the condenser) may leak, an issue that afflicted some latemodel GM full-size SUVs (Figure 3). And more recently, some
General Motors evaporator low-side line joints, on 2017-20 Impalas in particular, might suffer from leaks at poor welds.
For the super-hard-to-find leak, when dye alone isn't the answer, an SAE-certified electronic leak detector (J2791/J2913) is
the primary alternative, and with its three leak scales (4, 7, 14
grams/year) it may be used to indicate the size of a refrigerant
leak.
Dye doesn't indicate the size of a refrigerant leak, and the
only way to determine if a leak is small or large is how fast a full
charge escaped. If you installed a full charge (and only an SAE
Certified J2788 or J2843 recovery/recycle/recharge machine can
tell you that), and later used that machine to recover what's left
in the system, you should be able to tell the approximate size
of the leak. A certified machine is required to only pull out 95%
of the refrigerant, so you can't expect every last gram of the refrigerant charge to come out, but it should be close enough. The
current rule-of-thumb from SAE documents for a large leak is

August 2020

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if the system passed
the car maker's A/C
performance test after
the charge, but it lost
so much refrigerant
that it doesn't pass in
the same A/C cooling
season.
A related issue is
the J2843 requirement
that the R-1234yf machines perform a gross
leak test (0.3 gram/
Figure 3: Receiver-dryer cylinder
second) after refrigerant recovery, and if the integrated with condenser was
vehicle A/C system subject to leakage from plug on
fails that test, the ma- late-model General Motors fullchine should allow only size SUVs.
15% of the vehicle's refrigerant charge to be
installed in the system for detection with an electronic leak detector. The vacuum decay test that's in the J2843 standard specifies that the electronic detector probe be inserted through the
HVAC system's floor ductwork, up toward the evaporator. The
objective of the test is to determine that if the system has a gross
leak, that if in the evaporator, will be detected as a priority over
any other possible leak. The reasoning: R-1234yf is mildly flammable, so the greatest concern is to determine if it's getting into
the passenger compartment, where if somehow ignited, it might
pose the greatest danger to the driver and any passenger(s).
Although that's a logical engineering requirement, the technician has to find a gross leak no matter where it is in the system.
So, what does he do if the leak isn't from the evaporator, but all
of the refrigerant charge has leaked out? The J2843 machines
may only permit a single 15% charge, and some technicians
have encountered the problem of finding a gross leak elsewhere
in the system.
The makers of the machines do not provide a workaround,
but engineers at the companies informally agree these are possible ways to get a new charge into the A/C:
1. Turn off and then restart the machine, and if there
is no refrigerant left in the system (under 10 psi), you
won't have to go through refrigerant identification.
But you will have to go through the remainder of the
sequences to get to the gross leak test that allows installing a 15% refrigerant charge for leak detection.
2. Instead, close the coupler valves, which will make
the machine think there is no gross leak and it will
release refrigerant into the supply hose(s). Then you
can open the coupler valve(s) and enough refrigerant
should flow into the system for leak detection.
3. Use a tracer gas ("forming gas," which typically
is 95% nitrogen, 5% hydrogen) and an SAE Certified
J2970 tracer gas leak detector. We recognize that this
system is not overly convenient to use, and we don't
know how many independent garages have it. Yes, it's

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MACS Monthly Newsletter - 2020

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