MACS Monthly Newsletter - 2021 - DEC8

on (Figure 15), the PCM ramped up the cooling fan speed
to a desired setpoint, and when the A/C was turned off ,
(Figure 16) it ramped it down but never turned them completely
off .
Figure 18: Fan control displayed as ON.
Duty Cycle Testing of Variable Speed
Cooling Fans
Figure 16: Cooling fan runs slower, but still operating,
after A/C is turned back OFF
Scan Tool Active Tests
Bi-directional control of the cooling fans can be done
with any OE-capable scan tool. This test provides a quick
way to determine if the fans are functional, which can save
a lot of diagnostic time. See Figures 17, 18.
While the fans are being activated, we can monitor the
PCM-Fan Control (WH/BU) wire to determine if the PCM
is grounding the signal for the cooling fan control module.
Conclusion
Additional advanced scope level testing can be done to
determine the overall health of the cooling fans. Known
good test patterns of healthy cooling fan circuits is probably
a good place to start if a technician is looking to explore
these types of advanced level diagnostics as most
manufacturers typically do not provide these advanced
level waveforms. Once several scope patterns are analyzed
they can be put into the scope's waveform library
for later reference.
In summary, the electric cooling fans that are designed
to maintain safe operating temperatures for the internal
combustion engine (ICE), as well as hybrid electronics,
continue to evolve as engine technology evolves. Technicians
must continue to advance their skills in electrical
troubleshooting by reading, understanding and interpreting
all types of schematic diagrams. This helps reduce
stress levels when the time comes to begin analyzing circuit
types and any circuit deficiencies that may run hot.
Thanks for playing. Stay safe and be well! 
Figure 17: Fan control displayed as OFF.
MACS Service Reports is published monthly by the Mobile Air Climate
Systems Association. It is distributed to members of MACS and
is intended for the educational use of members of the automotive air
conditioning service and repair industry. Suggestions for articles will
be considered for publication, however, MACS reserves the right to
choose and edit all submissions.
Unless otherwise noted, all photos/art by author.
December 2021
8
Editors:
Production Designer:
Elvis Hoff pauir, Steve Schaeber
Laina Forcey
Manager of Service Training: Steve Schaeber
Mobile Air Climate Systems Association
P.O. Box 88, Lansdale, PA 19446
Phone: (215) 631-7020 * Fax: (215) 631-7017
Email: membership@macsmobileairclimate.org
Website: www.macsmobileairclimate.org
MACS Service Reports
Peter Orlando
Peter Orlando
Peter Orlando
http://www.macsmobileairclimate.org
MACS Monthly Newsletter - 2021

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