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Old 07-19-2014, 11:56 PM   #1
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Default Yes, Another AC issue, but different.

So just bought a used 02 Rendezvous that I am trying to trouble shoot the AC. Clutch not kicking in. I only have .3 volts at the pressure switch (red/blk wire) under the air box. Was able to trace and check ohms back to the ECM and no breaks in the wiring. That was for both the red/blk, supply voltage and the grey wire I assume is signal. I used the black and my multimeter to test the battery to ensure good ground.
I then moved to the AC Compressor itself at the three wire plug no volts there either. I didnt bother with the 2 wire plug until I get the pressure switch worked out. Checked fuses #2 under the hood and fuses 25 and 26 in the car, all were good. So can someone tell me what I should be getting on my meter and where. Thanx in advance to any and all.
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Old 07-20-2014, 01:58 PM   #2
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More than likely, you are low on freon, and that is why the compressor is not running.....

There are three wires to the a/c pressure sensor....grey(B) is the 5 volt reference voltage....black(A) is your ground....and red/blk(C) is your signal voltage......so with the sensor connected, and you back probe, B and A, you should get 5 volts.....back probe C and A, and you get the output signal to the PCM.......off the top of my head, maybe someone can help on this, I would assume you would get a reading of 1.0-1.5 volts, with the system not running.....anything near zero or 5 volts and the PCM will not allow the compressor to run.....

Unlike the pressure cycling switch on the Accumulator, the pressure sensor can not be jumpered....you can cause damage to the PCM.....

Normally you need at least 45 psi to start the system....pressure in the system(hi=lo with system off) is close to ambient......80F outside, should be about 80 psi in the system....pressure could be high enough to start, due to heat, but once the compressor engages, and low side drops quickly, the system will shut down....

the .3 volts reading you get may be too low, for the system to start.....
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Old 07-20-2014, 04:24 PM   #3
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Actually that is how all this began. I vacuumed and charged the system only to note how high the pressure was getting and the clutch hadn't engaged. So here we are. Here is the pressure switch where I'm only getting .3 volts on the red/blk wire and nodda on the grey. https://www.dropbox.com/*/bpd4vql54h...2014.40.56.jpg

Let me mention I did check with the ac and blower on but not with the engine running, as you can see the airbox had been removed. It is my understanding a way of checking the system is to look for voltage at the pressure switch with the power an ac on to determine if you have a sensor issue or electrical issue. With no voltage on the grey I would imagine an electrical issue it is. Now i just need to determine where or what supplies the 5volts to the grey wire. The PCM or the climate control module.

Here is the three wire plug by the Compressor i was referring to.
https://www.dropbox.com/*/i86nimxiwk...2014.41.48.jpg
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Old 07-20-2014, 04:50 PM   #4
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As I stated before, you need to have 5.0 volts on that grey wire....if you don't, it'* either open or a bad PCM......think you have a bad wire, if you back probe at the PCM and have 5.0 volts there........you will have nothing on the signal wire(red/blk) if you don't have 5.0 on the grey....thus no engagement...

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Old 07-20-2014, 07:24 PM   #5
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First off my sincerest apologies. I just noted I did not thank you for replying earlier. I was so excited to possibly have a solution my manners fell by the waist side, so a million thanx for taking the time to respond. A second thank you for posting the wiring diagram, exactly what I needed.

I did do a continuity test from plug to pcm and both b and c passed. I will reassemble everything and double check my findings here in a little with diagram in hand. But I suspect it is the PCM as I have null voltage at the grey wire. If my findings are consistent Ill find a replacement PCM and follow up on this post. Hopefully this will be helpful for someone else. Thank you once again.
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Old 07-20-2014, 11:16 PM   #6
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Remember one thing...if that line from terminal B to C2/34 is grounded, your continuity test will be good, but it won't mean anything...where it grounds you lose the 5 volts......I previously stated, that line could be open or a bad PCM...forgot to say it could be grounded somewhere in between and there will be no voltage at terminal B......You can verify this with a test light.....attach one end to battery positive, and probe either end of circuit 2700(both ends must be disconnected).....if the test light lights on either end, it'* shorted/grounded....
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Old 07-21-2014, 12:38 AM   #7
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Thanks for the heads up. I disconnected both the PCM and the pressure switch and tested end to end. If I remember correctly, red/blk was 24 and grey was 36 at the pcm. For the ground I connected my meter to it and the other end to the battery post to verify a good ground.
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Old 07-21-2014, 05:42 AM   #8
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Did you test for 5v WITH the engine running yet?
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Old 07-24-2014, 11:44 PM   #9
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Sorry so long guys, got dispatched to Knoxville for a few days..Yes Mike1995, I initially tried both with just power and the engine running. On the way I was able to hit a Pull A Part yard and grabbed another module..I am now getting my 5 volts. I also found a leak in the condenser. So ill install that and a new drier tomorrow after work. So hopefully after a vacuum I can proceed. If so and after charging the system Ill post my results Sat morning. Thanx to all for the suggestions and thanx Mike for the follow up.
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Old 07-28-2014, 12:52 PM   #10
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Success...finally. So in a nut shell it appears the previous owner tried to do some trouble shooting. When I picked up the car we talked shop a bit so he'* defiantly a DIY'er. The wires were riddled with probe holes right next to metal..I can just imagine a short or two when his probe hit the metal behind. So we started with an AC not working. So I checked for leaks by vacuuming the system and checking my needles every 30mins or so. Noted a slight leak, roughly 1cfm every 2 hours. So hoped leak sealant would do the trick. Charged the system, or tried when I noted my pressure was getting too high for only 20oz in. If memory serves correct it was at 80 and rising, so clutch should have kicked in. Checked fuses and all were good.
Pulled the car in the garage and let it cool down. Came back bout 3 hours later and noted a small puddle of green freon oil on the floor in the front. Looked through the grill and a steady bubble of freon was seeping from the condenser. That was a stroke of luck easiest leak ever.
Started my tear down, to look for the pressure sensor. I know it has one but cant see it. Eureka!! Hiding under the air filter housing. To my disappointment no voltage to be found. In all honesty I expected to see 12v, but thanx to Tech II providing helpful and accurate info I should have at least 5v. Not only that but what I should be getting on which wire.(thanx a mill) So double checked and still not even the 5 volts.
Pull A Part here I come. Found a PCM still in the air filter housing, SCORE!!! Only cost 35.00 SCORE. Sine I had to replace the condenser, I removed the AC Compressor to tear down the clutch plug to install some shrink wrap. One of the wires had been attacked by a razor, plus it was filthy from an old valve cover leak I'm assuming. While I had on my bench I added a crimp style T-Connector and about 3 feet of wire for future trouble shooting. So with the new/used PCM installed we have 5 volts now, great. Installed a new pressure switch as well. Reassembled everything and recharged the system. Got up to 80 this time but still no clutch. Grabbed my 3 foot wire and probed it, nodda. gave the fuse a once over again and its fine. Removed the radiator fan assembly to test the AC Compressor pressure switch now that were charged. Shows continuity between the pins, OK good. Pulled the relay at 52 and tested what would be the sockets for pins 87 or 30 for continuity with the wire I installed going to the clutch. Good tone at 30 so we know which pin is for the clutch and that the wiring from the relay to the clutch is good. Humm, bench tested the relay, its good. Applied 12 volts to my test wire and the clutch solenoid engages, OK so clutch is good. While I had the clutch working I charged the AC. Cleaned up, packed up, slept on it. While mauling everything over I figured that only left the fuse box itself.
Refreshed and thinking clearly I started with the AC Relay, I probed sockets for pins 87,85 and 86. We tested 30 the day before remember. 87 should be my 12v as its the N/O circuit for the clutch. As for 85 and 86 one should have 12v and the other ground, just wasn't sure which was which. So probed with the key on and off. I got ground at 85 and 12v at 86 with the key on. But nodda at 87 with or without the key, which should be 12v. Wiring underneath or pins must be damaged, disassembled the fuse box and low and behold.

https://www.dropbox.com/*/hdqpaff2bz...2019.31.40.jpg

Now I see why I'm not getting anything on 87. But I'm puzzled as to why I have key 12v at 86 as the wires are missing pins 86 and 87 altogether. Now I'm really confused. I'll be honest this really threw me a curve, I was confident it didn't come this way from the plant, and I know they have quality control, surely they would have noticed the AC not working. But I couldn't imagine someone doing this either. So to be sure I probed, then probed and probed again. To my relief the socket for 86 is shared internally with quite a few others, all originating from relay 60 the IGN relay. So that'* why I have 12v with the key at 86. So the black wire is fine were it is. So for my CSI moment. The pressure sensor goes bad but completely out of view, so someone, air quotes, probes every wire he thinks deals with the ac and shorts out the PCM. He then moves to the relay. Confused cause he has a good fuse and relay but no AC, disassembles the fuse box, test the wires, which is pointless cause our PCM is bad by this point. Saw were the black wire was and put the brown wire next to it thinking that'* were it goes. Which is why I take plenty of photos, cause I could so see myself making the same mistake. Summer here in Georgia is not for the faint of heart, so Craigslist it is. So I relocated the brown wire. rechecking my work, I now have continuity at 30 to the clutch, check. I have key 12v at 86 and key ground at 85, check. And at last constant 12v at 87. crossing my fingers I start her up and grin ear to ear as the AC compressor kicks in and blows ice cold air. And the best part, when I checked my manifold this morning I haven't lost an ounce of freon.

Thanks again Mike and Tech for your help.

Last edited by gixermann; 07-28-2014 at 12:54 PM.
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