06 civic lx engine dies at idle due to AC compressor stuck on

Aaron T

Respected
I'm working on a 2006 civic lx A/T that stalls at idle or runs rough. No DTCs set in the PCM but I discovered that the AC compressor is not shutting off causing the problem. I disconnected the compressor (connector right on top of the alternator) and now the engine doesn't stall anymore. The way I found the compressor wasn't shutting off was that when I was trying to figure out the rough idle I went ahead and revved the engine to about 3000 rpm to see if it would still stall (I was thinking low fuel pressure/volume) but instead it started making a weird sound (it sounded like the car was farting) and spraying something from the engine compartment which I noticed was the pressure relief valve on the AC compressor doing it's job, releasing excess pressure from the AC system. I then tried shutting off the AC with the buttons on the control panel and it showed AC off but I could see the clutch on the compressor had remained engaged. That's when I unplugged the compressor electrically and it disengaged the compressor clutch plus the idle went back to normal. So now I'm going to dig into what's causing the compressor clutch to stay on but just wanted to see if anyone knew of a common issue. The only recent repairs to the AC was an AC cooling fan (passenger side) but that was last year and this problem started yesterday.
 

Aaron T

Respected
boofoo said:
Sounds like two separate problems -- a short in the wire between the pressure switch and dash heater control panel and an A/C system fault (condenser fan doesn't run?) that causes the system to over pressurize.
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@boofoo, thanks for your reply, can you elaborate on how you came to those conclusions? I'm almost positive it's only one problem causing the compressor clutch to stay engaged because when I disconnect it electrically it shuts off
 


Aaron T

Respected
boofoo said:
If you actually turn on the A/C in the cabin, does the air blow cold from the vents, does the condenser fan run, and does the engine idle smoothly without stalling?

Do you have the A/C circuit diagram for your car? If so, post it.
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The compressor was on all the time regardless of what buttons I pressed in the cabin so I'm sure it would blow cold, as long as I had the blower fan on and temp set to cold but the only problem is that the compressor won't cycle off and the idle would go up and down then stall . I would have to reconnect the compressor and check the condenser fan. When I got to the car it was set to defrost but the blower fan speed was set to off. I selected dash vents to make sure the compressor shut off and left the blower speed set to off but still the compressor was on and it stalled the engine. I was more concerned with getting the car to not stall to be able to get it home since it left my sister stranded so I didn't mess with it more.

And no I do not have the diagram.
 

Aaron T

Respected
I believe I figured out the problem, I connected my scantool scanned the car, let the engine warm up, reconnected the AC compressor and went into the PCM data and noticed that it's seeing the command on/off from the AC switch when I press it on the dash and the condenser fan turns on when the AC is on and it blows cold out of the vents. Also the pressure switch is reading correctly it keeps climbing when the condenser fan is not on. I swapped the compressor clutch relay with the condenser fan relay (both Omron brand) and now the compressor shuts off when I turn the AC off. Looks like I'm buying a new relay
 

Aaron T

Respected
boofoo said:
If you actually turn on the A/C in the cabin, does the air blow cold from the vents, does the condenser fan run, and does the engine idle smoothly without stalling?

Do you have the A/C circuit diagram for your car? If so, post it.
Click to expand...
So, I checked the AC... It was blowing cold with it on and the condenser fan would come on with AC on and would shut off with AC off. The engine would still surge but didn't stall, I think I need to clean the throttle body. I swapped relays and fixed it

Compressor relay


Condenser fan relay

 
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