Dodge Repair: No AC compressor clutch: 91 5th Ave.

Question
Hello Roland,

The previous post would not let me reply, so here is my results based on your response.  

There is NOT 12v on Pin A while car is running.  There IS continuity  between 34 and Pin C.  The clutch does activate when I ground pin C.

Thanks again for your assistance.

have a 91 fifth ave 3.3 with a variable displacement compressor.  Problem is, it is not getting voltage so the clutch never engages.  I have shorted the DPCO switch and  the high pressure limit switch(also disconnected it).  I did not check the ambient sensor as I did the test on the control head and it didn't spit out any error codes.  I also checked all fuses in the glove box.

Can you tell me if there is something I am missing?

Thanks for your time and assistance,

Chris

ANSWER: Hi Chris,
You could start at the clutch relay in position #2 of the power distribution center. Remove the relay and jump 12v to the front pin of the socket and listen for the clutch to respond.
If that works, then try switching the clutch relay with one of the same part number (such as #4 or #5 which aren't critical)  and see if it will then activate the clutch when you request AC. If not, then ground pin 34 of the engine controller which should activate the relay. If so, then you need to verify the grounding pathway of the brown wire on pin 27 of the engine controller which starts at the blower motor speed switch, to the AC button, to the AC low pressure switch, to the high pressure cut out switch, to the ambient temperature switch and then goes to pin 27 AND the grounding pathway of the dark blue/pink wire on pin 31 of the engine controller that goes through the air conditioning fan cutout switch (on the compressor discharge tube and thence to ground).
To get the clutch relay actuation coil to close the relay you need to ground its wire at the controller, and that will only happen when those other two pathway wires are also grounded at the controller. Let me know whether you have the ATC or conventional control if you write back.
Thanks for the rating and nomination, as always.
Roland

---------- FOLLOW-UP ----------

QUESTION: Hello Roland,

I have ATC and held the three buttons for 2 seconds to put it in test mode.  I am assuming that since it came back with no codes and just powered down after the test that everything is fine there?

Thanks again for your time and assistance.
Chris

ANSWER: Hi Chris,
It appears to be unrelated to the ATC controller or the ATC per se. The only fuse involved with the ac clutch is fuse D (30 amp) in the power distribution center.
Roland

---------- FOLLOW-UP ----------

QUESTION: Thanks Roland, another question for you.  How do I ground pin 34 on the engine controller?  It is a big black bolted down connector and you cant back prob.

Thanks Again,
Chris

Answer:
Hi Chris,
That pin 34 wire dark blue/orange goes to pin C of the #2 relay in the power box, so to test the relay actuation circuit try slipping a thin insulated wire into the pin C socket, then replace the relay, then put the ignition switch in the run position, and finally ground the other end of the fine wire. The clutch should click if the relay and clutch are good. If it does then check for continuity between the #34 wire at the ecm plug and pin C socket, and verify that there is 12v on pin A of the socket with the key in the run position. The C socket is the outboard socket, and the A socket is the inboard socket. If you can actuate the clutch, then there must be an issue with either of the other 2 circuits I described which both have to be ground if the ecm is to ground its pin 34. Tell me your results if you can't get to the bottom of this issue.
Roland
PS: My only request is that you click on the "Thank/Rate the Expert" tab below. If my answer is helpful please click on the "Yes" button to give me a nomination for "Volunteer of the Month". Thank you

Answer
Hi Chris,
I believe you are mistaken about pin A in the relay socket not showing 12v with the engine running (or the key in the 'run' position) because it has to be there when you ground pin C for the clutch to be activated. That voltage powers many other devices necessary for the engine to run, so it must be present.
So basically I think that you have verified that the clutch actuation circuit is good, but that the engine controller is not grounding pin 34=pin C of the relay socket (assuming continuity between 34 and C via the dark blue/orange wire). So you should next check whether both pins 27 and 31 of the ecm plug itself are grounded when you have the AC request button pressed at the AC ATC controller. I suspect one or the other is 'floating'.

By the way, might you just be low on refrigerant in the system? That would be the most common reason for not clutch action. If the low pressure switch were "open" than that would cause the brown wire on pin 27 of the ecm to not be grounded.
Roland