MACS Monthly Newsletter - 2019 - JUL8

mazdaserviceinfo.com

Figure 11: Ambient temperature sensor on Mazda 3 is wired to BCM not CCU, although BCM can communicate with other
modules across wiring and a data bus.
provider if you need the help).
Just to prove the point, here it is:
* Set fan to high speed
* Temperature control to Max Cold
* Then, turn off the A/C and close doors and windows
* Wait five minutes, then unplug the evaporator temperature sensor connector
* Check temperature in the blower inlet (close enough
to the evaporator), and...
* Measure resistance at the sensor end of the connector
* Compare with the chart
The evaporator temperature sensor is a negative temperature
coefficient thermistor, the typical design, a temperature sensing
resistor in which the resistance goes down as the temperature
rises. So, if you do want to check one without a scan PID available, a generic resistance test is always possible, at least for an
open circuit issue to see if that's responsible for an A/C failure. ■

recharge the system. A quick check with the dealer told him that
the CCU assembly was about $500. Seems like neither is a good
choice if you're wrong.
We'll end the quandary by telling you he decided to change
the CCU and once he did, the system operated normally. But
there are a couple of aspects to this problem that could have
saved the anguish. First, because the refrigeration system
worked (after pressure switch replacement) with the control in
defrost, the symptoms do point to the CCU (or a bad connection, not found). But equally important, if he really felt the need,
he could have tested the evaporator temperature probe, without
a scan tool.
The procedure is in aftermarket service information (we
found it in AllData). There's a connector for the sensor under the
dashboard near the blower motor, and Mazda provides both a
resistance graph and a how-to test. I can't say the test procedure
is in an easy-to-find list, but if you rummage through the HVAC
service section, you'll find it (or call your service information
MACS Service Reports is published monthly by the Mobile Air Conditioning Society
Worldwide. It is distributed to members of MACS Worldwide 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 Worldwide 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 Conditioning Society Worldwide
P.O. Box 88, Lansdale, PA 19446
Phone: (215) 631-7020 * Fax: (215) 631-7017
Email: membership@macsw.org * Website: www.macsw.org

Unless otherwise noted, all photos/art by author.

July 2019

8

MACS Service Reports



http://www.mazdaserviceinfo.com http://www.macsw.org

MACS Monthly Newsletter - 2019

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