MACS Service Reports - 2016 - DEC1

Total Vehicle Climate and Thermal ManagementTM

December 2016

By Dave Hobbs - MACS Field Correspondent

Working with Complex Electrical Circuits
In this month's MACS Service Report we're going to take a look at working with complex circuits
along with the pros and cons of developing your
own 'free style' electrical diagnostics. What are
free style diagnostics? If you've ever thrown the
manual down after spending an hour or more going in circles with a trouble tree or symptom chart
you've had to make a choice;

things down. We'll start with the basics and work
our way down to the nitty gritty of this vehicle's
complex cooling fan circuit. Then we'll finish with
some extreme cautions using Power Probes / ammeters to source power or ground into a circuit.

Free Style Diagnostics
In order to even begin down the road of 'free
style diagnostics' you must make sure you're up to
the trip. If you've never really learned to ski very
well, you don't take off down the super steep alpine
slope w/o poles to try your hand with 'free style
snow skiing.' The same goes for electrical diagnostics. Anytime you venture outside of the comfort
zone of following written instructions, any lack of
firm knowledge related to electrical testing theory
of operation will become quite a hindrance. Take
for example Ohm's Law. You probably have an
opinion

1.
Give it your best educated 'guess' and throw
a part on the car.
2. Use what information you know / can find out
about the vehicle (theory of operation, electrical
schematic, connector pin out, etc.) along with critical thinking skills to diagnose the cause of the problem. That's 'free style' diagnostics.
We'll use two GM vehicles to illustrate: Testing
a GMC Savannah van's steering wheel controls to
break the ice regarding voltage divider circuits and
a real world case study involving a 2013 Chevrolet
Sonic LT with two problems;
1.
No start / no crank
2.
Engine overheating concern.

Dave Hobbs

Both are intermittent problems, of course! The
case study will take us into the complex world of
multiple relay circuits, complex schematics and how
you can easily simplify them! Personally I never
would have dreamed that a vehicle as spartan as a
Chevy Sonic would need 5 relays to control a single condenser cooling fan. I also never would have
dreamed how easy it would be to 'slip up' and start
a HUGE electrical fire by probing the wrong relay
terminal with a 'little juice.' More on that later. Regarding 5 relays for one fan, I suppose the cost and
complexity of a PWM cooling fan module was out
of the question for the OEM. A first step in diagnosing failures within complex circuits is breaking

Figure 1: Ohms Law basically states that the three units of electricity you measure with your meter are relational to each other. If you can test / find out what
2 of the numbers are in that relationship, you can do simple multiplication or
division to solve for the unknown value.

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

December 2016

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 Service Reports - 2016