MACS Service Reports - 2016 - OCT8

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hold the A/C and Recirc buttons, then turn the left temperature control knob one click clockwise. While you continue to
hold those buttons, all the vacuum fluorescent segments in the
display should light if the display is intact. If it isn't of course, the
whole panel has to be replaced. FIG. 12
Then release the buttons, the display will go blank and if it
stays that way there are no codes. All codes, including "historical" will then begin to display, but just for one second each.
However, once all codes are shown, the list will repeat until the
left side temperature knob is turned at least one detent clockwise
(or of course if the ignition is turned off).
Active (vs. historical) codes are indicated (if they are immediately logged) when the ignition is turned on, indicated by an
"ER" in the right side temperature display. We won't list all the
codes here (they should be in your service information system),
but there are three codes for a door not moving far enough,
which should tell you when a door is binding, perhaps from

Figure 12: 1999 Grand Cherokee on-board diagnostics can be accessed by
pressing and holding, then releasing the A/C and Recirc buttons. Any
trouble codes will be displayed. Also notice the infrared temperature sensors. Clean only with a damp cloth.

warpage. They are Nos. 15 (left side temperature door), 16
(right side temperature door) and 19 (mode door). In addition,
of course, there are specific codes for door actuators unable to
stop or not moving at all. ■

BY THE WAY: INFRARED TEMPERATURE SENSORS
Instead of a conventional in-car sensor with the little fan behind
the in-cabin grille, aspirator hose, etc., many Chrysler products,
starting with that Grand Cherokee, with dual zone Automatic
Temperature Control have had a pair of infrared temperature
sensors. They are built into the HVAC control head, in the center between the dual zone temperature control knobs (FIG. 12).
The sensor assembly has a wide-angle range for the dual zone

system, and replaces both the in-car and solar sensors.
These sensors are not repairable and if they don't work, you
have to replace the entire dual zone control module. The sensors
are basically life-of-car but they can be physically damaged, of
course, certainly if cleaned with anything but a soft, damp cloth.
Vinyl and leather dressings or spray cleaners can affect the sensing (and therefore the control system output). ■

WE ALL DO NOT-SO-BRIGHT THINGS
The blower motor didn't work on a 2013 Dodge Caravan with
Automatic Temperature Control, and the technician quickly excluded the motor itself with direct hot-wiring - it ran at high
speed. But there was an extensive circuit to check and he moved
the electronic blower speed control out of position in the intake
air duct so he could do circuit testing from the connection.
This system controls the blower speed by regulating the
ground, using a pulse-width-modulated input from the A/Cheater/ATC module and a feedback signal from the blower motor.
He traced the problem to the Totally Integrated Power Module, well actually the internal relay which by itself is not replaceable. So he installed a replacement TIPM (from a wrecking yard,
but it was clean and the customer was on a tight budget). Inasmuch as a new one is over $500, that's understandable.
After installation, the blower seemed to work normally on all
speeds, but after running a while, it was down to low speed. He
shut it off for a while and tried again, and once more it seemed

to be normal, but not for long. He tried driving the car and got
the same results, but then he realized that the normal operation
resumed if he waited a while.
The "AHA" moment: the blower speed module was not seated in the air intake duct and so its heat sink was not cooling it
down until the system was shut off. Why didn't he reinstall the
module? His reason was that he didn't want to reassemble everything until he was sure the system was fully operational, so
that he could resume circuit testing if necessary. But in failing to
reassemble, he created another problem.
We can understand the desire to be sure a repair is successful before total reassembly, particularly if there's any real difficulty in the process. However, some HVAC case actuators also
can encounter a problem if you try to test the system without
reinstalling them, as they lose alignment when they operate outside their position in the case. Further, with a dislodged blower
speed control there's also the possibility of heat damage to the
case and/or module. ■

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.

October 2016

MACS Service Reports

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