Pcm A/C output Voltage to compressor

Edward Owner Texas Posted   Latest  
Unsolved
HVAC
2011 Jeep Compass 2.4L (B ED3) (CVT2)

Good Evening 

I have a question on A/C voltage output from the ECM to an direct drive variable displacement compressor. PWM circuit , have 6.07v on my Scope don't see a square wave, with the connector disconnect with no voltage change when turning the ignition or Hvac switch on or off. Not understanding the ECM Strategy here…

My understanding is 12v with a square wave 

What am I missing

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Interesting
Darren Technician
Wisconsin
Darren
 

dtc?

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Edward Owner
Texas
Edward
 

Good Evening DARREN NO CODES FOUND

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Jonathan Technician
Ontario
Jonathan
 

Is it only when unplugged? It could be a bias voltage that the module uses to check the circuit for shorts or opens

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Edward Owner
Texas
Edward
 

Good Evening Hart YES, I didn't try back probing the circuit Hart but I will get a confirmation on Monday with my Scope. But I believe your correct on the bias voltage.. Thanks again for your input

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James Owner/Technician
New York
James
 

Did you read the description of operation as far as how the ac system works…. Also check for a short to power and what problem are you having with the ac system….

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Edward Owner
Texas
Edward
 

Good Evening James I read 📚 most of the SI information couldn' see anything on strategy for the ecm. I will check on Monday for basis voltage and back probe the circuit and see if I get my 12v PWM signal Thanks again for the input

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James Owner/Technician
New York
James
 

Description

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Helpful
Darren Owner/Technician
Arkansas
Darren
 

James, you might have missed what Edward is working on. The vehicle used 2 distinctly different types of compressor drives depending on application. Edward is working on a variable displacement system which does not use a clutch (in the normal sense) His compressor dive pulley is constant engagement with a break away drive insert (in case of compressor failure) and uses a variable swash plate to…

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James Owner/Technician
New York
James
 

The tipm is a know failure point I run my own shop and work for mopar dealership

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James Owner/Technician
New York
James
 

I would say short to power in that harness or a driver shorted internally in the pcm

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Richard Instructor
Florida
Richard
 

have you scoped it with the compressor connected? Once you unplug that connector, the pcm most likely recognizes the circuit is incomplete and disables the driver.

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Agree
Martin Owner/Technician
New York
Martin
 

I have to agree here and with the connector off it may just be a default response to what now seems to be an open circuit. I have learnt to best check circuits with load applied, the dynamics are all different.

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Agree
Edward Owner
Texas
Edward
 

Good Evening Martin Lesson learned, it makes sense I will check on Monday for basis voltage @ 6v disconnected and then back probe the circuit and see if I get my 12v PWM signal this will confirm the theory.. Thanks Martin

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Edward Owner
Texas
Edward
 

Richard Falco I will check on Monday for basis voltage and back probe the circuit and see if I get my 12v PWM signal. This makes sense now Thanks for your input 👍

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