8th Generation Honda Civic Forum banner

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Discussion Starter #1
I have a 2008 Honda Civic 1.8. Initially, my understanding was that the ac was not working. From reviews, I started with the relay and replaced it and this did nothing. After research, I attempted to jump the compressor, and the clutch would not engage. I replaced the compressor and now it engages and is working properly. I replaced the low pressure switch as well, which changed nothing. At the relay box, I am able to jump the power side of the clutch relay and cause the compressor to operate manually. On the control side, there is power, however, there is no ground, I am able to jump the ground directly and the compressor will turn on, however, it has constant power, the control panel does not affect it. But would the control panel affect the ground side of it, causing it to lose connection? This has all pointed me to the control panel, but I was hoping to gain more insight. I am learning all of this rapidly, but I have very limited knowledge of this. Thank you for your help!
 

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The control panel grounds out the wire leading to the thermal protector (part of the compressor) to make sure the compressor is not overheated. The control panel provides power to the compressor clutch (it is grounded to the compressor case so that is why there are only three wires on the A/C compressor connector.

I assume you checked to make sure the system is charged?
 

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Yes, the system is charged. I checked to make sure it wasn’t overcharged and not lacking. I did manually jump the compressor and ran it intermittently, and it was blowing 43 degrees from the vents. However, it won’t do it on its own.
 

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I pasted pictures of the wiring harness. I think you're going to have to trace the wiring from the control panel to the A/C compressor conector and from the fuse box to the connector.

Both wires go through a big 23 pin connector near the brake fluid reservoir. That might be a good place to start.

Good luck.
 

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The ground side of the compressor relay control is provided by the PCM. It takes all of the inputs (i.e. AC button position, fan switch position, pressure switches, etc.) and decides when to provide a ground for the control side of the compressor relay.

You did a fair amount of "jumpering" wires. If you accidentally jumpered the control side of that relay socket you very likely could have burned out the transistor driver inside the PCM that controls the relay. The best way to check this would be a bidirectional scan tool that can engage the compressor.
 

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Hey a John, didn’t know you had a civic! To original poster Take John’s advice. He’s been around Hondas for years and typically will outgun most Honda service techs!


Sent from my iPad using Tapatalk
 

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Nah, I don't have a Civic, but I work on them when someone brings me a broken one. I joined this forum a few years ago when a tech that was on here finally solved the idle relearn mystery on the Internet and used the Foxwell tool to reset.
 

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Discussion Starter #12
Well, I don’t have a bi directional scanner. However, I did find several used but guaranteed pcm’s for $40-60. So, idk.
 

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For working on these vehicles you really need a bidirectional scan tool. In 5 minutes you can connect, pop into activation tests and engergize the compressor clutch. If it activates via the scan tool then the output driver is fine and you have an input problem (pressure sensor, etc.)

You can't just pop in a used PCM either because the vehicle won't start due to the theft deterrent system. It won't recognize the key and won't allow you to start it.
 

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Discussion Starter #15
Yeah, I have a friend with a scanner that is going to check it for me.
As far as the pcm, what does it take to program it?
 

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Professional level scan tool at the very least. It often depends on the vehicle and the manufacturer but sometimes requires a J2534 programming box and computer with subscription.

My point is it's much more cost effective to get this professionally diagnosed than to just start throwing parts at it. You'll pay $100-150 for programming plus the cost of the PCM to just "try it." Your money is better spent diagnosing it properly.
 
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