MACS Monthly Newsletter - 2017 - NOV1

Total Vehicle Climate and Thermal ManagementTM

November 2017

By Paul Weissler - MACS Senior Field Correspondent

LESSONS A SHOP OWNER SHOULD LEARN
debris left in the system.
For openers, the technician hotwired the clutch, and
the system ran and had normal pressures. This seemed
to confirm that the compressor replacement was followed by a recharge, the system charge was normal,
and the compressor installation was not the problem.
Although of course there could have been something
else that was temporarily solved with the compressor,
so we can't criticize the approach.
And in this case, the technician next started by scanning for codes, but when he found none, he checked
for blown fuses. Here again there were none, so he decided to test the high-pressure cutout switch, which
was conveniently located on a Schrader-type valve.
No difficulty locating it, and no fault here either. He
felt he could continue on the belief the system charge
was good, so the next question in his mind was whatever was controlling the cycling of the compressor.
Simple fact: he had no idea what the sensor/control
circuit was for cycling the compressor. He checked
the HVAC case for an evaporator temperature sensor
because the last Navigator/Expedition system he had
serviced was a 2005-on model (actually a 2009 model), and that's what it had. But there was none on this
model, and now he had no idea what to look for.
He next looked at the wiring diagram, and without a
description of how the system works, he felt lost. One
issue was that he was looking at just part of the circuit
(Figure 1). That part covers the central junction box,

There are some lessons a professional shop owner
should not only learn but embed in his active memory.
One of them is to know the operation of the system
you're working on. We confess that in these times,
knowing every system is impossible, so we're modifying the lesson to be "look it up before you spend a
lot of diagnostic time." And that includes systems that
are anything but new, because even with older cars
you've worked on, there's no way you'll remember
the details.
Ford systems are likely to be most familiar because
Ford is either the #1 or #2 brand, depending on model
year. But even within the Ford family, there certainly
are lots of variants, and in this particular case we're
focused on the 2003 Lincoln Navigator/Ford Expedition.
The system (electronic automatic A/C) had the usual symptom; no A/C clutch engagement. But a new
compressor already had been installed. However, one
thing we've observed over the years is that when a
previous failure has been corrected by replacement
of a specific component, a technician invariably goes
back to that job, with the view that something in that
area was either missed and not repaired, or was serviced incompletely or improperly. We can't say that's
the worst idea, because we've seen enough to point
a finger that way. And with compressors, there's always the strong possibility that a failure led to related
service issues that were not attended to, particularly

ALSO INSIDE THIS ISSUE:
THE PRICE OF R-1234yf AND THE ILLEGALITY OF A RETROFIT .............................................................................. 3
MORE THAN ONE ISSUE? WELL NOT REALLY ............................................................................................................ 4
LATE MODEL FROM A BODY SHOP ............................................................................................................................. 5
A NEAT LITTLE TOOL KIT ................................................................................................................................................ 7
CAN'T SAY IT OFTEN ENOUGH ...................................................................................................................................... 7

MACS Service Reports is the official technical publication of the Mobile Air Conditioning Society Worldwide, Inc., P.O. Box 88, Lansdale, PA 19446. The material published in MACS Service Reports expresses the views of the contributors
and not necessarily that of MACS. Every attempt has been made to ensure

November 2017

the accuracy of the content of MACS Service Reports. MACS, however, will
not be responsible for the accuracy of the information published nor will MACS
Worldwide be liable in any way for injury, labor, parts or other expenses resulting
from the use of information appearing in MACS Service Reports.

MACS Service Reports

Table of Contents for the Digital Edition of MACS Monthly Newsletter - 2017