MACS Monthly Newsletter - 2021 - OCT4

performance the motorist will notice on a hot day).
The compressor shaft seal has been an issue for decades
for several reasons: 1) all shaft seals leak, even if it's just 5-10
g/yr. Of course, that leakage occurs when the compressor is
operating, not when it's off, so the annual loss past a good
shaft seal may be very small; 2) the nose of the compressor
often has a well that holds oil, and perhaps even a fabric seal
that absorbs any oil. So, you may have to take off the clutch to
get to the oil accumulation. 3) the clutch is not typically easily
accessible for removal.
A few are, a few are not most. Which is why an electronic
leak detector is often about the best you can do with the
shower cap method (Figure 4). Wrap a shower cap around
the nose immediately after A/C shutdown, wait a half-hour
or so, then push the probe of an electronic detector through
the cap. Our experience is that if you get an SAE certified
electronic detector to alarm at the compressor nose, and nowhere
else in the refrigeration circuit, including the evaporator,
it's likely " the source. " v
That Refrigerant Flow Sensor
In the May issue (by Dave Hobbs) and the June issue (by
yours truly) of MACS Service Reports, we discussed the
Toyota refrigerant flow sensor. Dave showed applicable
waveforms for the circuit, and then referred to an aftermarket
replacement sensor. I discussed the entire assembly, which
includes a spool valve and magnet (Figures 5 through 12 in
the June issue, Figure 5 here), in addition to the electronics in
the sensor connector.
The " magic number " for sensor voltage is 3.7 volts. Toyota
says that if the A/C is off (engine on) and the voltage is below,
perform a series of harness checks (in Toyota TSB -0084-13)
between the flow sensor connector and the amplifier (A/C
control unit).
Also check voltage with the A/C on, and if the voltage is
under 3.7, the system may simply be undercharged. Evacuate
and recharge the system to specs with a recovery/recycle/
recharge machine known to be accurate, and if the system
was undercharged, clear the code and see if the issue is resolved.
In
either case, if the harness and its connections are good
and there's a full charge, and the B1479 flow sensor trouble
code returns, Toyota says to replace the compressor. It does
not provide a replacement sensor, and as we pointed out in
the June issue, the sensor assembly that is sold in the aftermarket
is strictly the circuit board built into the connector. It's
cheap, easy to replace and therefore easy to understand why
it's something you might want to try. The part sold in the aftermarket
is not from DENSO, but made in and sourced from
China.
However, here's an example of why not to use it. The technician
in our case first tried to get by with a used DENSO
compressor, and despite an evacuate and recharge, the system
didn't work and the voltage readings were borderline
to low. He pushed down on the connector, and the voltage
readings went up and the compressor would briefly operate.
So, he installed a so-called " replacement sensor, " sold by an
American aftermarket company (but sourced from China)
and the readings dropped to around the one-volt mark. This
seemed to indicate an issue with the spool valve assembly,
which was raised in our cautionary notes in the June issue. So
finally, he bit the bullet, installed a new DENSO compressor
from Toyota and the problem was solved.
The bottom lines: as we noted in the June issue, the fault
Figure 5: DENSO compressor flow sensor assembly is
more than just a circuit in the connector. As shown, it includes
a spool valve assembly with two springs, and a
magnet.
October 2021
4
very well may be in that spool valve assembly. A used compressor,
say from a wrecking yard, may have originally been
replaced for the very same reason. And while that aftermarket
replacement so-called " sensor " may work briefly, we suggest
you don't provide any warranty on A/C performance with the
job. v
MACS Service Reports
techinfo.toyota.com
http://techinfo.toyota.com
MACS Monthly Newsletter - 2021

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