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A/C clutch wont engage;


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srwa
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Jun 11, 2018, 1:31 PM

Post #1 of 18 (511 views)
A/C clutch wont engage; Sign In

 
2001 Dodge 2500 diesel 5.9L vin.7....Jumped relay pin 30 to 87...clutch engaged.. Installed another relay....there are 7 identical relays in this truck each doing their on thing. Relay good....Pulled the relay part way out, pins still making contact, grounded pin 85...clutch snaps into place hard & solid.. Checked high & low pressure switches,good, freon good.

Everything kinda/sorta pointing to the PCM.....That ain't good.

Pin 30 has bat. voltage at all time,pin 87 is a n/o switch,pin 87a not used in tghis app., pin 86 has bat. voltage when the key is on & the a/c in the cooling mode. Pin 85 is the clutch coil ground controlled by the pcm...

Am I missing something??


srwa
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Jun 11, 2018, 2:50 PM

Post #2 of 18 (502 views)
Re: A/C clutch wont engage; Sign In

One more thing....When everything is working normal and the a/c is turned on bat. voltage is applied from pin 30 to pin 87 closing a n/o switch between pin 30 & pin 87 to provide power to the clutch coil....also, back at the ranch,and at the same time the pcm will apply bat.voltage from pin 86 thru a resister & solinoid inside the relay to pin 85 for the clutch coil ground.

BUT, the pcm ain't providing the ground.
Now, one possible "fix" is to cut the pcm clutch coil ground, blk/white tracer,, wire coming out of connector C (gray) of the pcm in cavity 1, run it thru the firewall thru a toggle switch to a good ground and control it that way.

Recon that'll work???......should.


Hammer Time
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Jun 11, 2018, 3:27 PM

Post #3 of 18 (491 views)
Re: A/C clutch wont engage; Sign In

Just because the PCM isn't providing trigger ground doesn't mean the PCM is at fault. It isn't going to send that signal until it is satisfied with all the inputs that it monitors.

The dash switch sends a ground signal to both the PCM and the high pressure switch on the lt grn/wht wire. It travels through the high pressure switch to the low pressure switch and back to the PCM. All these things need to take place before the PCM will send the trigger signal.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



srwa
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Jun 11, 2018, 3:57 PM

Post #4 of 18 (487 views)
Re: A/C clutch wont engage; Sign In

Thanks for your reply;


Have jumpered both the high & the low pressure switch connectors, singly & together, the pcm will not ground the clutch coil.


Hammer Time
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Jun 11, 2018, 4:00 PM

Post #5 of 18 (485 views)
Re: A/C clutch wont engage; Sign In

You may have jumped the switches but you haven't verified that they are receiving the signal from the control head.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



srwa
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Jun 11, 2018, 4:04 PM

Post #6 of 18 (481 views)
Re: A/C clutch wont engage; Sign In

"You may have jumped the switches but you haven't verified that they are receiving the signal from the control head."

Thats gonna take a drb111 scanner witch I don't have........yet.
Unless you know of an other way?


Hammer Time
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Jun 11, 2018, 4:09 PM

Post #7 of 18 (474 views)
Re: A/C clutch wont engage; Sign In

If you read what I typed earlier, it's very easy.

You are looking for ground on that wire from the control head, all the way back to the PCM after going through the switches. Ltgrn/white going out and brown coming back.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Jun 11, 2018, 4:10 PM)


Hammer Time
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Jun 11, 2018, 4:13 PM

Post #8 of 18 (470 views)
Re: A/C clutch wont engage; Sign In





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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Discretesignals
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Jun 12, 2018, 6:37 AM

Post #9 of 18 (437 views)
Re: A/C clutch wont engage; Sign In

Now, one possible "fix" is to cut the pcm clutch coil ground, blk/white tracer,, wire coming out of connector C (gray) of the pcm in cavity 1, run it thru the firewall thru a toggle switch to a good ground and control it that way.

Recon that'll work???......should.


Quote
Bad idea. The clutch has to be able to disengage in the event of excessive high side pressure or if the thermal switch opens to keep the evaporator from freezing. Besides that you know someone is going to forget to turn the switch off.






Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Jun 12, 2018, 6:51 AM)


srwa
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Jun 12, 2018, 10:00 AM

Post #10 of 18 (424 views)
Re: A/C clutch wont engage; Sign In

"Bad idea. The clutch has to be able to disengage in the event of excessive high side pressure or if the thermal switch opens to keep the evaporator from freezing. Besides that you know someone is going to forget to turn the switch off."
Your right. The pcm is not grounding the clutch coil.
As HammerTime stated, I need to trace the ground circuits out.

Thanks for your post.


Discretesignals
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Jun 13, 2018, 6:21 AM

Post #11 of 18 (396 views)
Re: A/C clutch wont engage; Sign In

One thing you can do if you can find someone or get hold a scan tool that can do an ATM test is to see if the PCM (driver) has the ability to pull the voltage to ground. Any enhanced scan tool should have the ATM function.

An ATM test is a special function that Chrysler have that will actuate all outputs on and off in a timed manner. It's a great way to see if there is a driver or wiring problem between the PCM and the relay coil or you need to look at PCM inputs. The ATM test bypasses all inputs and actuates all the outputs.

You take a 12 volt low amp test light connected to battery positive and probe the terminal in the relay cavity for the relay coil control and activate the test. The test light should flash on and off to tell you the output side and the PCM are fine.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Jun 13, 2018, 6:23 AM)


Tom Greenleaf
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Jun 13, 2018, 7:05 AM

Post #12 of 18 (391 views)
Re: A/C clutch wont engage; Sign In

Outside of the box thought: swra: Have you checked where they diagram shows grounds? The A/C clutch is actually quite strong a load to pull in if a ground was missing, connected but just not good usually corrosion or messed with things will seek strange other ways and still work but the clutch is a stronger load than many things.


Just back power a test light preferably an incandescent bulb but any. Ask the item to work and see if ground straps lose it or if looking lousy undo, shine up with sandpaper, wire brush and reattach them if any question. It's a 2001 even water/dampness can screw up just a connection at just the wrong spot is why there are more than one thru a vehicle. It would be on my maybe list and rule it out,


T



srwa
User

Jun 15, 2018, 8:37 AM

Post #13 of 18 (354 views)
Re: A/C clutch wont engage; Sign In

Thanks for your post. Question:

"An ATM test is a special function that Chrysler have that will actuate all outputs on and off in a timed manner. It's a great way to see if there is a driver or wiring problem between the PCM and the relay coil or you need to look at PCM inputs. The ATM test bypasses all inputs and actuates all the outputs."

"You take a 12 volt low amp test light connected to battery positive and probe the terminal in the relay cavity for the relay coil control and activate the test. The test light should flash on and off to tell you the output side and the PCM are fine."

Scuse my egnertz, but, are above to be done together?


srwa
User

Jun 15, 2018, 8:55 AM

Post #14 of 18 (351 views)
Re: A/C clutch wont engage; Sign In

Thanks for your post.
Been offline since Tuesday morning. Road const. about a mile South, contractor cut a Uverse trunk line. Did the same thing last week.

Will check the grounds.
Got batt. voltage at cavity 1 of the pcm out of terminal 86. According to the book that ain't right; should have batt. voltage on 86 coming out of fuse 11 in the junction box when the key is on & calling for a/c. Then when the switch is closed between terminals 30 & 87 the pcm switches to ground thru terminal 85 from terminal 86. All this thru the a/c relay.


Hammer Time
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Jun 15, 2018, 9:12 AM

Post #15 of 18 (345 views)
Re: A/C clutch wont engage; Sign In


Quote
Got batt. voltage at cavity 1 of the pcm out of terminal 86. According to the book that ain't right; should have batt. voltage on 86 coming out of fuse 11 in the junction box when the key is on


I don't understand what you are saying there. Yes, you should have voltage on Term 1 of the PCM with key on.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



srwa
User

Jun 15, 2018, 1:43 PM

Post #16 of 18 (326 views)
Re: A/C clutch wont engage; Sign In

Sorry about that. The uploaded scanned pages didn't work.


Hammer Time
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Jun 15, 2018, 1:47 PM

Post #17 of 18 (318 views)
Re: A/C clutch wont engage; Sign In

This can't go on forever. Instead of trying to post more stuff, why don't you do the testing you were provided 16 responses ago?



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



srwa
User

Jun 15, 2018, 1:55 PM

Post #18 of 18 (312 views)
Re: A/C clutch wont engage; Sign In

You are absolutely correct.
Goodby.






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