MACS Service Reports - 2016 - OCT7

mode valve, and cables for the temperature (blend-air) and recirculation doors too (FIGS. 10a and 10b). The cable seemed to
operate, but he was finally on the right track and when he dug
into the dash, he found that when the radio was installed, the
installing technician had pinched the blend-air door cable. So
although the cable seemed to move, it didn't transfer full motion
to the door linkage. Simple enough when you find it and fix it.
And A/C cooling was back to the 40's F.
During this long run, the Colorado/Canyon did have an Au-

tomatic Temperature Control available as an option. But the
low-cost manual system was the choice even on the particular
vehicle in this case, which was a top trim choice with the 3.5-liter
V6, not the base four-cylinder.
Everything changed with the new series, and even the manual HVAC is an electrical/electronic system with motor actuators
(FIG.11). So naturally there are no cables to kink, but the usual
possible assortment of electrical issues. ■

ONCE AGAIN: THE PROBLEM WITH ANOTHER CAUSE
We wouldn't be surprised to get the same 100% diagnosis
response from a lineup of experienced A/C technicians for the
description of this problem: 2000 Nissan Xterra V6, compressor
goes off but if you turn off the A/C switch for a few minutes,
then push the A/C button the A/C comes on and runs for about
20 minutes. As the line goes, "repeat as necessary," but the result
is always the same. A look at the diagram makes the problem
apparently obvious: a bad evaporator temperature sensor. And
the truth is that the evap temp sensor is a common failure on this
system.
Okay, the evaporator temperature sensor gets replaced - but
the problem remains. As the diagram shows, this system has
two other sensors that also might be responsible: 1) the refrigerant pressure sensor on the condenser and that (2) triple-pressure
switch/sensor. The fans work normally? Well, fan control is
the function of that triple-pressure switch, so that apparently is
okay. And there's an output from the condenser pressure sensor, which is a rare failure item anyway. This DKC (now Bosch)
compressor has a thermal switch and to cover another base, it
was replaced.
The pressure gauge readings are absolutely normal when tested in the shop. However, the compressor itself is almost 17 years

old, has been used in a hot southwestern climate, the problem
has been tolerated for some time through a number of the aforementioned parts replacements, but remains. We're not in favor
of installing compressors without some evidence something is
wrong.
There is no updated software for the system, and a scan tool
connection does not indicate a PCM command to disengage.
Is the compressor clutch still engaged at the time the A/C
stops? If not, does a screwdriver against the drive hub get it to
quickly re-engage, indicating a weak clutch (check the amperage)? Or maybe the clutch is engaged but the compressor is
binding when the A/C stops. Doesn't have to be a lockup, just
a temporary bind. Is the compressor body hot? At 350 F. it will
trigger that thermal switch as a proper reaction. On high cooling
load in hot weather, that can do it.
With an intermittent A/C stoppage of this type, you have to
work quickly (while the problem exists) to identify an issue,
which was traced to a marginally weak clutch coil, a maximumspec clutch gap and some signs of singeing on the clutch faces.
The compressor was 15 years old, so a replacement unit was
installed. Yes, sometimes the causes fall into the mundane category. ■

ON THE OTHER HAND
The 2012 Chevy Cruze with the 1.8-liter four-cylinder also
was experiencing a loss of A/C (warm air blowing), but in
this case when coming to a stop, particularly in stop-andgo traffic and it seemed most often on hard braking. The
technician at first considered checking for a large clutch gap,
maybe a loose connection, or even a sharp torque-related

movement of the engine causing a tug on a harness. But he
did notice that the connected scan tool indicated the PCM
was commanding the compressor off. So he began his diagnosis with a check of service bulletins, and sure enough
there was a software update that addressed the issue. Logical move; good result. ■

HOWEVER, WE HEARD NOTHING ABOUT...
In the June, 2016 issue of MACS Service Reports, we discussed
a poor cooling problem on a 1999 Jeep Grand Cherokee with
the 4.7-liter V8 and dual-zone Automatic Temperature Control.
After replacing the variable orifice tube and receiver-dryer, and
recharging to specs, the cooling remained poor. The technician
tried to see how the HVAC case doors were operating, and digging into the case he eventually concluded the problem was
with the blend-air door.
However, we suspected he didn't realize the HVAC electronic control system has on-board diagnostics, because we heard
nothing about the technician using them, which include a series
of automatic tests. We're often hearing about this non-realiza-

October 2016

tion, previously on a Hyundai system (MACS Service Reports,
May 2016 issue). So we think it's apparently an area that technicians have decided that if it isn't in their scan tools, the diagnostics aren't there.
Here's another example of where they are available. Naturally they look for no response or over-response, but two of them
were directly related to the poor cooling issue: one is for mode
door not moving enough, two others for left and right temperature doors not moving far enough.
The display will list diagnostic trouble codes in ascending numerical order.
The on-board system is easy enough to access: just press and

MACS Service Reports

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