MACS Monthly Newsletter - 2021 - MAR8

Four Seasons

Dave Hobbs

Figure 14: Current Ramping BLDC Motors. For HVAC electric motor applications, there are no known external
3-phase circuits to capture a current ramping waveform
from. However, in the 3-phase BLDC fuel pump world,
this figure shows what one phase's current ramping pattern looks like. Looks like AC - going both positive and
negative in polarity as each phase is pulsed.

Figure 15: BLDC Scoping? This Four Seasons BLDC blower
motor has three wires, but they are NOT connected directly to the three phases. You could scope the power
wire with an inductive amp clamp, but it would simply
be a consistent flat line of current. The module attached
to the blower motor assembly takes the DC power and
turns it into a 3-phase DC current signal, just like the
3-phase fuel pumps found on some vehicles today.

ure 14) before condemning the actual fuel pump. 3-phase
BLDC motor usage is also spreading to other electric motor applications such as ABS, transmission pumps, and
EPS (Electric Power Steering).
Even though there are plenty of HVAC 3-phase BLDC
motors in service (Figure 15), there are no HVAC related
applications with external circuits connecting to 3-phase
motors to date. Therefore, we'll spare the details (for now)
on how to diagnose these complicated circuits. Rest assured, we'll be ready with information and training at
MACS the moment we start seeing external 3-phase motor control circuits that effect the HVAC tech, in order to
help you to stay ahead in the game! v

to the typical 2-wire DC motor. Why all the complexity?
Elimination of the brushes and other design advantages
makes the 3-phase BLDC electric motor more energy efficient, which brings down the drive belt load for the alternator or DC-DC converter load on the HV battery in the
case of HEVs and EVs. This in turn assists with fuel economy and emissions. Increased longevity due to the lack
of brushes to wear out later is an additional benefit. For
3-phase BLDC fuel pumps, knowing how to diagnose the
three phases WILL be on your agenda to learn. 3-phase
BLDC fuel pump control modules are rarely integral to the
fuel pump assembly which means that you must be able
to diagnose the control module and 3-phase wiring (Fig-

MACS Service Reports is published 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.

Editors:
Elvis Hoffpauir, Steve Schaeber
Production Designer:
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: info@macsmobileairclimate.org
Website: www.macsmobileairclimate.org

Unless otherwise noted, all photos/art by author.

March 2021

MACS Service Reports

http://www.macsmobileairclimate.org

MACS Monthly Newsletter - 2021

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