MACS Service Reports - 2016 - OCT6

SO SIMPLE TO FIX, EXCEPT...
The problem: a leak on a 12-year-old Mercedes-Benz E-Class
with the 5.0-liter V8. Probing the system with an electronic leak
detector identifies the source at the receiver-dryer. Straightforward: replace the dryer, evac and recharge, but the compressor
doesn't engage - A/C light flashes when it's pressed, indicating
there's a code.
However, the shop's scan tool, although it's a top professional
brand, doesn't cover A/C. Although many of the A/C-related
codes (and certainly the clearing of codes) are powertrain codes,
which reasonably can be expected to be covered. In this case
the code is a powertrain number, but it's a manufacturer-specific
one (P1999), and Mercedes - specific codes (and the ability to

clear them) are not necessarily on every tool.
There is no disconnect-the-battery or other alternative procedure to clear any codes, and in any case, it's a good idea to be
sure that the only code is related to the low refrigerant from the
leak. In this situation, the technician had to borrow a scan tool
with the capability to check and erase what turned out to be the
only code.
Moral of the story: make sure your scan tool has real capability, and keep it up to date. Further, the $99 tool with just "generic
OBD" doesn't cut it. There are lots of medium-priced tools that
will cover an A/C specialist's needs. ■

ANOTHER CASE WITH A FAMILIAR SYSTEM, BUT A TOTALLY DIFFERENT CAUSE
cause many of these aftermarket radios have a lot of features the
base OE radio did not, such as Sirius, etc.
In this case he'd have tried operating the cables - yes, the manual HVAC on Colorado and GMC Canyon has a cable-operated

The Chevrolet Colorado and GMC Canyon have been on
the market for a number of years, and since its introduction the
manual HVAC system has been a pretty basic design, all the
way through to the 2014 model, last of the series. The mid-size
trucks were completely redesigned for 2015 model year.
The motorist's complaint was poor cooling (of course) on
the manual HVAC system, and inserting a thermometer in the
center outlet confirmed the problem - above 60 F. with the temperature control set to full cold. The technician started with a
pressure gauge test and found they were high with the compressor cycling at what he thought was a rapid clip. Instead of
going through a full range diagnosis, he replaced the expansion
valve (seems like a waste to us, although he convinced himself
that the rapid cycling had slowed down, but with no obvious
improvement in cooling performance).
One of our sure-fire ways to begin any job is by asking the
customer about the vehicle history. Although just looking at the
control stack would have raised the question: "did you get the
original radio replaced?" He sure had - lots of people do, be-

Figure 11: New Colorado/Canyon manual HVAC uses electric actuators,
such as this one for mode control, held to HVAC on mounting studs.

Figure 10: Cables are used to control manual HVAC on pre-2015 Chevy Colorado/GMC Canyon. Shown are connection to flap door actuating cam (10a)
and to a mode control knob on the control stack (10B).

October 2016

MACS Service Reports

Table of Contents for the Digital Edition of MACS Service Reports - 2016