MACS Monthly Newsletter - 2020 - JAN2

If you do come across a core that leaks, don't be too quick to
toss it. Compare it to a new one and see what you find. We did,
and the new spring was much stronger and stiﬀer than the old
one (Figure 2), and held the seal closed much tighter, too.
Sure, this procedure is going to take a few extra minutes to
complete, and it's not likely to be found in service information.
But like the case of the F-650, it could help you diagnose a leaker!
Note: Some may argue that it doesn't matter whether a valve
core is capable of staying closed under vacuum, since the system is
normally charged with refrigerant and operating under pressure.
For the most part, that's true, but there are special circumstances
where this becomes an important service issue, which we'll explore
in a future MACS Service Report.

the cap and placing a leak detector near the valve core to see if
it's leaking, but this is not a valid test. Even the sealing material
that's used to seal the core against the inside of the housing has
a certain permeation rate which, by itself over time, is going to
leak refrigerant into the small space between the valve core and
the top of the sealing cap. It's not much (somewhere on the order
of 0.020 grams per year), but over time refrigerant will build up
under the cap. Same goes for the even smaller seal on the valve
face itself.
That's why your leak check should begin by leaving the service port cap in place. If no leaks are found, then you've ruled
out the service port as a potential leak site, and you'll have to
continue searching elsewhere. See Figure 4.

How are valve cores being tested now?

Steve Schaeber

One of the lines I left out from the story above said this: "As
OEMs continue improving their systems, technicians are seeing leaks more often attributed to the valve core that's down
inside the service port fitting, either on the high or low side of
the system. Most of these leaks are discovered while the system
is charged and under pressure." This is based on years of survey
data we've received from MACS member shops, which show
valve cores as the most commonly repaired leak source.
However, we're not sure that valve cores are as much the
problem as may be the diagnostic methods being used to test
them. So, we set out to learn how it's being done, and here's the
typical scenario:
Technician suspects a refrigerant leak is causing a performance issue, and first checks the system for any dye leaks that
can be found. When there are none, the ELD (electronic leak detector) is next to come out, and after a quick survey of the A/C
fittings and connections, service port caps are removed, and the
probe placed near the valve core. See Figure 3. As you can guess,
the detector goes oﬀ, "beep beep beep" to indicate a leak. The
technician surmises the valve cores to be the source of the leak
and replacing them is the fix sold to the customer.

Figure 4: Leak testing should begin by looking for dye and "sniﬀing" around the service ports BEFORE removing the caps.

Steve Schaeber

If you do find a leak with the cap securely installed, you
should remove it, but don't be too quick to sniﬀ. First, inspect the
cap thoroughly, including an inspection of the cap's o-ring seal
(usually up inside the top of the cap). If that's OK, save the cap
for reuse, otherwise, throw it out and replace it. Then, inspect
inside the service port for any oil or dye, which may indicate a
leaking core. Also check for dirt or debris which may have contaminated the port. It only takes a few tiny specs of dirt to get in
the way of the valve core's seals, not allowing it to close properly.
But if the port is clean, you still have one more step before sniﬀing for a leak: blow out the residual refrigerant. You're likely to
find an amount of refrigerant under the cap of just about every
vehicle (you've probably heard that little "pssst" sound when
you open the cap), even ones that are brand new, and if your
ELD is sensitive enough it's probably going to trigger. That's
why you need to clear out the port reservoir before testing.
And here's another curveball: Refrigerant is "sticky", in
that it tends to "stick" to the inside surfaces of the service
port even after the cap is removed. Plus, we know that
refrigerant is heavier than air, so if you were to simply
remove the cap and not blow out the port, you'd likely
trigger your ELD.

Figure 3: Most common answer: "I popped oﬀ the cap and
my detector triggered, so I swapped out both cores."

A better way to test

An A/C microcosm

The fact that valve cores are an easy, quick way to "find and
fix a problem" that may or may not be the root cause of a specific
performance issue should not be a surprise. In other words, the
service ports are right there, the cores are relatively cheap and
easy to replace, and ELDs often trigger when placed near them.
Hence, part of the reason for the increase in valve core replacements found in our surveys.

A service port should not be thought of as simply the connection point by itself, but rather a little "system" of individual
components that make up the "service valve assembly". That
means the port housing (what the service coupler connects to),
valve core, spring, seal(s), o-ring(s) and cap all need to be in good
condition and work together to seal the service port.
When testing for leaks, many technicians start by removing

January 2020

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MACS Monthly Newsletter - 2020

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