MACS Service Reports - 2015 - FEB5

technicians that have considerable Honda experience confirms
that this is a standard Honda HVAC engineering approach that
you'll see on other Honda products.
And one more: a 2008 BMW 5-Series with Climate Control
in Auto. With the cabin at 95°F, the airflow from the A/C registers is in the 60-70 degree range. Switch to manual (Max A/C)
and the air flow temperature drops to the low 40's. So the refrigeration system obviously is okay. Switch back to Auto, and the
temperature control moves to increase the temperature of the
airflow from the A/C registers.

The temperature sensors check out, so the logical thought
seems to be to change out the control unit. However, the answer
is in a trimming menu in the A/C control system setting, which
the driver (or another driver in the family) accessed at some
prior time. The menu has a box with four plus and four
minus settings, which trim the upper airflow in the Auto
mode. If the highest plug setting is chosen (as it was),
the A/C register air will be warmer than in the automatic program; if a minus setting is chosen, the air will be
colder. ■

SO IT'S NOT PLUGGED, THERE'S NO AIR LOCK, WHAT ELSE CAN IT BE?
LET'S LOOK AT ACTUATORS

rent fuse, that surely is it. However, on many GM cars the
HVAC is controlled by the Instrument Panel Integration
Module and if that's the battery current fuse you find,

February 2015

gmtechinfo.com

In the January 2015 issue of MACS Service Reports, we
discussed causes of poor heat, but said we'd save for this
issue a short discussion on a specific case in the area of
actuators, particularly blend-air (temperature) actuators.
When you can't trace a heating problem to an issue
within the core, or with system coolant flow, most technicians conclude there has to be a problem with the temperature (blend-air) door, and they're right a high percentage of the time. The actuators fail, the linkage breaks
or the door binds. And in older cars (or a few simpler late
models) the control cable kinks or binds in its housing, or
the linkage jams.
If you can get to the actuator, you usually can hear (or
not hear) if it's operating. Even if the problem is poor
heat, there should be some perceptible movement when
you change temperature settings.
Shops seem overly anxious to change actuators. Well,
they do fail a fair number of times. And check that connector. One of the saddest stories we've heard was a technician who replaced what he thought was a defective
actuator on a late-model General Motors car, installed
what turned out to be the wrong actuator even though
it fit, and concluded it was a defective part. When he finally got the right part and installed it, he found it didn't
work. The reason: it needed to be initialized. Had he just
disconnected the battery ground cable and reconnected,
it would have automatically recalibrated. But he used a
computer saver before disconnecting, which normally is
the procedure that maintains pre-sets and previous performance. So the computer never lost power and therefore never went through the automatic initialization.
Every system has a procedure for initializing the actuators, and GM actually offers two methods: 1) with
the scan tool special functions menu; 2) with ignition
off, remove a specific fuse for a minimum of 60 seconds,
then reinstall, turn ignition, engine and HVAC on. There
actually are GM circuits where as little as 10 seconds is
enough, but not all. Take no chances and give it the full 60
seconds (and maybe a couple more to be sure).
You'll probably go for the fuse pull unless you have a
high-end scan tool, but it's not always so simple.
First, which fuse is it? If there's an HVAC battery cur-

Figure 6: To initialize actuators on GM cars, the HVAC battery fuse has to be
pulled for a minute, but where is the fusebox? On the 2002 Pontiac Bonneville
and 2003 Olds Aurora, it's under the rear seat on the left side (2 in the illustration). Other part shown is (1) the lateral acceleration sensor.

pull it. The fuse box location varies from under the hood
to under the rear seat, to the left of the battery. And sometimes the GM OE service information doesn't tell you, so
you'll just have to look around. We found the under-seat
fuse box on the 2002 Pontiac Bonneville and 2003 Olds
Aurora, both models built on high-volume GM platforms, so don't be surprised if you see it on others too.
Even after finding the fuse box, you then may have to
check the wiring diagram to find out which number fuse
is the one to pull (typically a 10-amp fuse). See Figures
6, 7.

BUT BEFORE YOU CLOSE THE BOOK ON
CHANGING THE ACTUATOR
If you can physically get to the linkage, make sure the
door operates normally. An actuator that clicks while operating improperly may be an obviously-needed replacement. But if the linkage and/or flap door are bad, the
new actuator won't solve the problem. ■

MACS Service Reports

http://www.gmtechinfo.com

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