MACS Monthly Newsletter - 2020 - MAR7

both fuel pumps and A/C compressor clutches, one would only
assume the same failure could be responsible when your customer's TIPM equipped Chrysler, Dodge or Jeep has no power
output to the compressor clutch.

(Figure 4).
4. The TIPM also uses an analog input from the A/C system's pressure transducer to determine system pressure
to enable or inhibit A/C clutch operation (Figure 4).
5. TIPM provides a single wire discreet (digital, as in either high or low but not pulsing) output to the ECM /
PCM. This information circuit from the TIPM (connected
to the ECM / PCM) is referred to as "A/C Clutch Control
Output". The importance of this circuit is to let the ECM
/ PCM know the A/C clutch has been applied for the
purposes of idle speed boost / load management. Don't
confuse that circuit with the other circuit with an identical
title which provides power to the actual A/C clutch coil
(Figure 4).
Beyond A/C clutch duties, the TIPM handles blower motor
operation in one way or another in an equally complex manner
(Figure 10), bringing me to my final point in careful diagnostics.
Always analyze not only the circuits you're working on but also
the accuracy of the information shown for those circuits. n

A/C Clutch Control - TIPM Style

FCA

Most vehicles employ a data bus signal from the HVAC module to the ECM / PCM requesting the A/C clutch to engage. If
there are no reasons for the PCM not to turn on the A/C (such as
an overheated engine, excessive engine load, etc.), the PCM will
then trigger a relay (plugged into the fuse panel / relay center)
to then carry out the apply of the A/C clutch.
With many FCA vehicles utilizing a TIPM, the process is far
more complicated:
1. Driver presses A/C request button on HVAC module.
2. HVAC module sends TIPM an A/C request message
via the vehicle's CAN IHS data bus (Figure 9).
3. TIPM utilizes its internal relay mounted on its non-serviceable PC board to turn on the A/C clutch relay power

Figure 10: A larger look at the HVAC control module, front blower module, rear HAVC control head and TIPM on a 2013
Dodge Caravan with auto temp control. The HVAC control module is clearly in charge of controlling blend, mode and recirc
actuators so if you're getting a symptom related to those devices, you're staying inside the van with your scan tool and meter
when diagnosing. When it comes to symptoms of inoperative blower motors (front or rear) the TIPM has traditional plug in
style relays for both on the top next to its fuses. How those relays are triggered is another story. The front blower motor still
uses a remote blower control module (solid line circle) signaled by the HVAC control module to give the right PWM signal
for desired fan speed. The HVAC control module / switches at the rear HVAC blower controls (upper right in schematic) are
wired through the HVAC control module and provide the signal to the Rear A/C Heater Control module (dotted line circle)
for it to provide the rear blower motor the correct PWM signal for the desired blower speed.

When the Book is Wrong
Law, high resistance causes an undercurrent condition,
NOT an overcurrent condition! If you read the factory
trouble code chart further, you'll be advised to use a test
light and observe how "bright the bulb is" while probing
the clutch output. I'm sorry, but that's stone age diagnostics. Going further, the factory service manual's theory of
operation / data PID list implies that the PCM controls
the A/C clutch (Figure 11).

How to Handle Service Manual Inaccuracies
(2013 Dodge Caravan Example)

Have a DTC P1275 (A/C clutch control circuit overcurrent) stored in the TIPM? Forget following the published
flowchart. The factory website's flow chart lists high resistance in the clutch coil along with high resistance in the
circuit to the clutch as possible causes for this condition.
Apparently, service engineers were either understaffed
(in a hurry and didn't catch the typos) or didn't understand electricity at all. The last time I considered Ohms

March 2020

I don't mean to pick on FCA - they have some of the

MACS Service Reports

MACS Monthly Newsletter - 2020

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