MACS Monthly Newsletter - 2022 - DEC5

Obviously, pin height is important for coupler engagement.
R-134a and R-1234yf use different pin
heights to help prevent cross-contamination, but
the individual valve cores are the same. In the pictures
of assembled service ports, the pin heights
between the two R-134a high side ( " charge " ) valves
are clearly different - is one of them out of spec?
See Figure 10.
SAE J639 does not define the coupler travel below
engagement with the valve core pin to open the
valve core. Instead, the final pin depression height is
specified within 0.5mm [0.020in].
What do all these definitions mean for servicing
the A/C system? The maximum allowable travel for
a valve core pin in an R-134a or R-1234yf system is
only 2.2mm [0.087in]. If the service coupler is not
properly adjusted, the coupler pin will mis-stroke
the valve core. In some cases, opening the core too
far can limit the flow rate of the refrigerant, just like
not opening the core far enough. Not all valve cores
can be over-stroked without damage. But,
it 's not
practical to measure the location of the valve core
pin and adjust the coupler for every use, and some
couplers do not have adjustable pin travel.
Currently, MAC refrigerant quick-couplers are not
Figure 10: Valves Left to Right: R-1234yf Low Side with
Standard Core, R-1234yf Low Side with North American
M8 Core, R-134a High Side Integrated Valve, R-134a High
Side with M10 Core.
SAE J639 allows a 1mm [0.025in] total tolerance
for the system breech of seal, for both R-134a and
R-1234yf systems. While breech of seal officially
means " refrigerant communication with the A/C system, "
most valve manufacturers design their valves
to have a pin height within the breech of seal range
when properly installed (Figure 11).
well defined by any J-standard. SAE J2888 does indicate
that R-1234yf couplings shall be compatible
with SAE J639, but this has left enough latitude in
coupler design that service ports can still be damaged
by the R-1234yf quick-couplers. The new standard
would clearly define the correct limits of the
coupler pin stroke and sealing interfaces to properly
service the MAC system without damaging any part
of the service port (Figure 12).
Figure 11: SAE J639 dictates that the valve core pin height
at breech of seal be between 9.3 - 8.3mm below the valve
mouth for R-1234yf systems, and 7.1 - 6.1mm below the
valve mouth for R-134a systems.
December 2022
Figure 12: Both of these valve cores were returned for
warranty evaluation from an OEM customer. The damage
to the valve core pin on the left is a typical outcome of
pin overstroke due to a misadjusted coupler. Both valves
have a concerning amount of contamination present.
5
MACS Service Reports
Schrader Pacific
Schrader Pacific
Schrader Pacific
MACS Monthly Newsletter - 2022

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