MACS Service Reports - 2015 - JUN7

ducer didn't help.
The high-side service valve is in the front section
of the liquid line. Pressure gauge readings were not
unusual, so there would be no reason for the transducer or connected pressure gauge to show anything. The answer is pretty simple: the condenser
is restricted. Although the discharge pressures got
high enough to blow open the pressure relief valve,
the condenser restriction moderated the pressure
rise at the service valve and transducer.

Not a tough problem at all, most of us would say,
at this juncture. But it takes a broad diagnostic view
to keep something like that in mind. We've talked
about checking for a large temperature drop across
the condenser (35-50°F) and we've also noted that
it's difficult to take a delta-T reading on the condenser of most modern cars. Infrared guns have to
be used carefully and aimed precisely for this purpose, with probe type thermometers often more accurate. ■

A/C GROAN
ing there. He double-checks the power steering
with a helper turning the steering wheel back and
forth, but still no answer.
The technician feels the high-pressure line and
yes, there's some vibration, but no affect on groan.
The condenser fan came on when the system high
side pressure went over 220 psi, which comes across
as normal.
Okay, that's all the visual stuff, and what's next is
a check for an applicable service bulletin. There are
several A/C bulletins, but nothing seems to apply.
We would suggest that you read through all bulletins in the time period that might refer to moan
and vibration, because although the complaint was
about moan when the A/C is turned on, that could
well be just the symptom that shows up when the
cause is elsewhere.
That said, the technician finally decides to just
look at the engine while a helper turns the A/C on
and off. With that step he can see that there's excess
vibration from the engine, which leads him to inspect the engine mounts. He spots oily goo at one of
the mounts and therein lies the answer: a hydraulic
engine mount leaked out its fill of oil. The fix for a
defective mount (hydraulic or rubber) starts with
replacement of the mount of course, but on many
cars should be followed up with an alignment procedure for the mounts. Check the service information.
We'd like to note that there's another possible
cause on some cars that gets traced back to the engine mount: a diaphragm type mount with an electronic control unit that duty-cycles the diaphragm
to cancel vibration at idle and in some cases just
off-idle. A bad diaphragm, poor electrical connection or leaking mount could increase vibration and
although engine vibration itself is unlikely to be
noisy, as the MINI example shows, it can produce
noise. In that case, A/C-on groan.
Many Lexus (and other cars) have an electroni

techinfo.toyota.com

You may think that a bit of noise with the air
conditioning turned on is not the highest priority
item for a motorist. After all, if the car is running
and the A/C is cooling, what's the big deal? Well,
that works for a while, but then the noise gets to
the driver, and although he might not be willing to

Figure 9: Lexus electronically-controlled, fluid-filled engine mount also
adds a vacuum solenoid valve with a diaphragm, to counter low-rpm vibration.

break the bank to fix it, he doesn't want it to continue. It's beyond just annoyance: if it isn't normal,
the motorist is likely to believe that it is something
wrong, and unless it's fixed, is likely to lead to an
expensive repair.
So the car is in the shop and in this case it's a 2005
MINI, although it could be any one of a number of
cars. The technician begins with the most obvious
possibility: is the compressor mount tight? Yes it
is. How about the drive belt? The technician looks
for a rumble at the compressor pulley and doesn't
see anything that even resembles a slight wobble.
Next step is to check the power steering and water
pumps both visually and with a stethoscope; noth-

June 2015

MACS Service Reports

http://www.techinfo.toyota.com

Table of Contents for the Digital Edition of MACS Service Reports - 2015