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Discussion Starter #1
I've been working on this one with my dad for a few weeks and looking for some direction, advice or personal experience!

The A/C in the car works intermittently, and seems to be getting worse over time, but that could be my imagination. At this point the A/C rarely works.

The problem as far as I can tell is that the Clutch is not being commanded to engage the compressor. When the A/C is working everything appears normal and the air blows perfectly cold.

We started with the Auto Active test and that passed, so my understanding is that the IPDM is not the problem. We checked the pressure on the high and low side when the clutch decided to work and the readings appeared normal. Based on the pressure readings we got and the A/C blowing cold when it is working, I don't believe that the problem is a leak or low refrigerant. We also tested the refrigerant pressure sensor and that gave us 1.4 V when the system was not operating and 2.4 V when it was working, the service manual I have says anything between 1-4 V is in range, so I think the refrigerant pressure sensor is OK. I don't think the problem is the Clutch or the Compressor either because when the clutch is not engaging we are not getting power from the IPDM to command the clutch to engage, leading me to believe that the problem exist upstream from the IPDM or within the IPDM if the auto active test doesn't 100% rule it out. We checked some of the wiring between the Front Air Control and the Body Control Module following the flow chart in MTC-39 found here https://cardiagn.com/manual-air-conditioner-versa-2012-h/ and thought that maybe there was an issue with the BCM and swapped it out, but we're experiencing the same issue with a different used BCM. We depinned wire 10 out of the IPDM which is where the IPDM sends power to the clutch and gave it power to see if the wiring from the IPDM to the clutch is good and we got the clutch to engage on that test. For some reason the IPDM is not sending power to the clutch even though we are commanding A/C at the Front Air Control. Things get a little tricky to test between the BCM and the IPDM because they are connected via Can line communication and we don't have the tools to see what kind of data is flowing over that line. When we hooked up a 2 way OBD2 connection the ECM would show an intermittent command for the A/C as well. The A/C signal is getting lost somewhere in the computers (IPDM,BCM,ECM) or before that.

My dad's big question is that when looking at BCS-13 https://cardiagn.com/body-control-system-versa-2012-h/ , the manual shows a test for the "compressor on signal" and when we hook up the probes instead of 0 V and 5 V for an A/C Switch On and Off respectively we are getting 0 V and System Voltage, some 13 V give or take. Any thoughts on why that would be?

Our big question is what would cause the IPDM to intermittently send power to the clutch when it passes the auto active test? any good ways to test the can lines? is it possible that there could be a problem with the signal from the Front Air Control?
 

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Hamstertree, I know this thread was from about 2 weeks ago, but I wanted to check in with you on your troubleshooting if you haven't figured it out already. The 13V reading with the A/C switch off is certainly cause for concern and sounds like a short circuit somewhere. I would look into isolating the cause of that first and it may correct the whole compressor clutch issue. The BCM is looking for a value of 5 on that input signal to detect that the A/C switch is off and likely is confused by an input value of 13. Looking at BCS-13, which you referenced, the two wires in the BCM harness adjacent to the A/C switch input both supply system voltage levels, with pin 28 (pink wire, blower motor circuit) constantly at system voltage and pin 26 (green wire, thermo control amp) intermittently pulsing to near system voltage then dropping to 0V, potentially implying a damaged or mis-pinned BCM connector. If everything checks out on the BCM connector side, check the same circuits coming out of the A/C control head (front air control).
 

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Hey Fredo, thanks a ton for your reply! I’ll have to do some follow up and check this pin again. We did end up finding what we think was the problem. I also posted in the new member forum introducing myself and asking for help with the A/C. What we found was by swapping out the thermo control amp the A/C started working. Our thought is that the thermo control amp went bad and was commanding an A/C off. If I had to guess it accomplishes this by grounding or possibly shorting the A/C compressor signal which is why we were seeing what we were seeing when we back proved the BCM, but definitely worth another look!! This is our “extra” car so I haven’t taken the time to put the glove box and trim all back together yet so I’ll double check the voltages when I get the chance.
 

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That thermo control amp is kind of what I was thinking about based off of the signal it sends out and the symptoms you were describing.
 

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We picked up a thermo control amp from the junk yard and had to disassemble almost everything in the front of the car in order to remove the ac unit and access the evaporator where the probe end was installed. To test it we simply unplugged the old amp and plugged in the used one from the junk yard which is easily accessible in the drivers footwell. I’m going back and forth on whether or not I should take the time and effort to properly instal the thermo control amp. Disassembling a junk yard car is one thing, disassembling and reassembling my own car is something else.

Any thoughts on the risks of driving without a properly installed thermo control amp?
 
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