Mike, quick video on how to check that the PCM is controlling the AC clutch relay control circuit !!

 

Pressing the Front Defrost, Rear Defog and Fan Up buttons simultaneously, updates the temperature display instantly


This table was posted recently by oelarse:

 

 

Thanks so much to all you guys. I wish I knew half as much as you guys, like C5 DIAG, GCG, BILL CURLEE, etc. Have no intention of quitting in this search. BUT-I spent from 5:45 A.M. until 8:00 P.M. away from home travelling to car dealer 70 miles away, fixing our daily driver. Left $1,400.00 poorer!! Long story on warranty work, some covered some not. So my time, and $$ has been considerably used up. Well get to the bottom of this guys, with YOUR help. I'm considered a pretty good mechanic, but know very little about electronics, except how to install power lamps, speakers, and head units in cars 40 years old, or older!!! Thank you, again. Have all kinds of codes now, but last Tuesday car was dyno'd and the window valet was removed and reinstalled, and yadayadayada. Will get back to it, and you all ASAP.

 

My guess is either your climate control isn't functioning find that fuse location for the ac control or the unit uts self has stopped sending the signal and is spent. My other guess replace the a/c condenser and or check the belt. Most likely if your not getting that click it's one of the 2! Both parts can be picked up used fairly cheap!

I've noticed sometimes you have to turn the system off for a few seconds after switching which way the air flows or if I just press off sometimes the fan stays running and when your try to press the a/c button it will revert back off after a sec or 2! I found powering off the control then starting it with the a/c button and the button switched on the cabin air circulation the curved button not the air vent with the straight arrow has been my problem solution! My belt is also worn so when I come to a stop in hot weather the a/c will lack it's full ability to produce cold air! After I start moving 2mph or so it will pick back up. I know I need a belt change though. When I removed it for my s/c install it had taken a permanent shape and was dry hard rubber! This could also be why the a/c shuts off because it lacks belt tension to operate! Just a guess.

 

No problem Buddy !!...just let me know if you watched the video and understand what’s being done...if so I’m going to delete the video from my channel !!

 

At least you are persistent in your troubleshooting.

 

I'll watch video today, Rob. Been really busy. But I got the test light!!! Funny, I did have a test light at one time. After getting the DVM, I gave it to my daughter's boyfriend, and they broke up!! Oh well, got one now that will stay put!!!!

 

Thanks Rob, I watched video. Well done btw!!

 

Can't do much today, but tomorrow I'm on it!!!

 

Things changed, so I just went out and checked pin #85 for ground. When A/C button is pushed, NO LIGHT-NO GROUND FROM PCM. BUT-With key OFF, the light lights and there is a faint "clicking" coming from the fusebox!! With key on, but engine off, no light-No clicking. Also, when moving down the road at 50mph, the A/C light was coming on a few days ago, but of course, it wasnt working. Today I tried it again before I checked pin 85, and the A/C light would come on for maybe 5 or 6 seconds, then go out!! Anyway-Going back out and try again, this time I'll try the re-circulate A/C "MAX" button, instead of the "outside air" button, and see if there is a change. Will report back in a short time, if possible. Thanks guys

 

UPDATE!! Tried same test on pin #85 with re-circulating button with same results: No Ground to pin 85 UNLESS key is off. If the key is on, with OR without engine running, no ground to pin 85. So at this point, I'm kinda dead in the water.......

 

Hey !!...did you check for ground to pin 85 with ENGINE RUNNING AND AC ON ??...will NOT work with key on or off...let me know if you did it this way so we can figure out how to proceed !!... the test light should not come on with key OFF...if so you may have a short to ground on that wire...if that is the case you would have to disconnect the harness connector at the PCM and using an ohm meter do a short to ground check !!...means getting the right front tire off and getting underneath the car and access that connector !!

 

Good info to know, especially the button combo. Amazing how the C5 can do so many things by pushing a combination of buttons! Like self diagnostics, key fob relearn, TPMS reprogram, etc..

 

Don't despair we already knew that... Results are as as expected. Excerpt from Post 39 above (I also gave you a couple of ideas to explore - check it again):

 

Is the schematic you posted for a 2000 ??...my SI for a 2000 and also my C5 Pinout sheet shows Pin 43 (dark green/white) being the Clutch AC Control... now with his 12v test light only being LIT at Pin 85 with the key OFF only he may have a "short to ground" in that circuit...the only time the clutch relay control circuit is energized is when you press the AC button as in the video I posted for him....MMMMM ?????....a bi directional scan tool would be needed to command the clutch relay on and off but if the test light stays lit when connected between pins 86 and 85 there is a short to ground !!...thanks !!

 

It's on the lift. Will get connector off PCM and check it out. Thanks all

 

It's from a '97, so if your 2000 schematic says it's Pin 43, instead of Pin 39, for the 2000 PCM A/C Clutch Control, then it's Pin 43. Could you please post your schematic to make sure we are in sync with our circuit references?


This is what we know for sure:

• Engine running - Pressing A/C button: no ground to Pin 85
• Key OFF: Pin 85 is grounded

As I mentioned in Post 39 above and then again in Post 55, the reason Relay 34 is not activated while pressing A/C button with engine running is because Pin 85 is not being grounded. This was an expected result, as per the circuit analysis.

I have never checked the status of the PCM A/C Clutch Control (Pin 43) with Key OFF. I would have expected it to be open, but I haven't verified it, so I don't know if OP's Pin 43 is behaving abnormally or not.

As it can be seen in the schematic, Pin 86 is only hot in ON and START (through Relay 42), so Pin 85 being grounded in OFF doesn't do anything to Relay 34. In other words, when the ignition switch is in OFF, Relay 34's coil may have ground in one end, but it doesn't have power in the other. Again, I haven't verified if what's happening to Pin 85 is normal or not.

Just to be thorough, I would suggest to verify the integrity of CKT 459, but I would also suggest to look for possible causes that may be forcing the PCM not to allow the A/C clutch to engage.


If I understood him right, it wasn't that the test light stayed lit when the ignition switch went to OFF, while connected between Relay 34's pins 86 and 85. As mentioned above, that would not only require 85 to be grounded, but 86 to remain hot with Relay 42 de-energized. I interpreted it as he testing pin 85 to battery positive with ignition switch in OFF

 

Thanks !!...OP checked at the PCM and it is Pin 43 (dark green/white) so no big deal !!...with engine off he said the test light lit when probing Pin 85 connected to battery Positive...the light should NOT come on if the AC Clutch Relay Control PCM driver is open (I verified this on my car key OFF)...OP said he just checked for "short to ground" and is good as per "how to do a short to ground check with an ohm meter"...LOL !!...when PCM C2 connector was unplugged test lit did NOT light this time...that is telling me that the PCM driver is stuck closed with key OFF !!...I HATE AC !!!

 

Many thanks to you guys. Today I checked everything C5diag and you suggested. I also verified continuity between pin #85 at the fuse box and female Pin#43@PCM. It checked O.K.. I also checked Male pin#43@PCM for continuity (or was it voltage? Maybe both-Sorry-Maybe C5diag can clarify last statement) to ground. There was nothing coming from the PCM either way; With key off OR key on. Starting to think PCM is bad.... Anyone care to chime in, or give your 02?