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Discussion Starter · #1 ·
Hey all! I'm curious if anyone has run into this or can offer advice. 2011 Civic (I believe DX trim, it's low-end, 4-door, fabric seats, the works). Thank you in advance, this week without A/C has been brutal.

Symptoms:
  • A/C not working. Green LED light comes on on HVAC control panel, but air does not get cold. The A/C compressor clutch is not engaging, but both fans are running.
  • I have this model of HVAC/heater control panel for reference, the one without a digital display built in. I discovered that the vent direction control buttons are not working (what is the proper term for these? The ones that control whether it's defrost or pointed at your face or feet). The air is stuck on defrost, blowing at the windshield.
  • I noticed driving at night that, when the headlights are turned on, the backlighting behind most of the HVAC control panel buttons do not come on. See photo where 4 different buttons (Max Cool, A/C, and two of the vent positioning buttons) are not lighting up. I know it's possible that the bulbs simply went out, but I think it's an odd coincidence.
Diagnosis thus far:
  • I originally thought this was exclusively an A/C issue. I replaced the relevant fuses (No. 36 in under-dash fuse/relay box; No. 12 in the under-hood fuse/relay box) and the a/c relay, but this did not fix the issue.
  • I ran the self-diagnostic function on the heater control panel and got 4 blinks - which seems to be "DTC Indicator 4: An open or short in the mode control motor circuit".

I am just wondering why the mode control motor would be related to the A/C compressor not engaging. If it were the mode control motor, wouldn't the compressor still run and the cold air simply wouldn't make it into the car interior?

I am not terribly experienced with electrical testing so I'm not sure how to proceed from here, but I do own a multimeter and follow instructions well!
 

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I have literally the exact same issues... Been researching the last few days extensively. I'm starting to think the HVAC control unit might be the culprit. But not sure yet. Gonna work in it today.
 

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The A/C clutch is commanded from the HVAC control panel in the dash through a digital message to the PCM, which fires the low side of the relay to turn on the clutch.

You can check the clutch, but taking a wire and jumping the relay pins. If the clutch comes on the air gets cold, then you know you don't have a mechanical problem with the A/C system. Instead it's an electronic control problem.

If the HVAC control panel has a code, many times it won't allow the A/C clutch to fire. You need to resolve that code first which in this case means fixing the blend door problem. It could be the motor or it could be the HVAC control panel which seems to directly control the motor according to the schematic.
 

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Discussion Starter · #4 ·
The A/C clutch is commanded from the HVAC control panel in the dash through a digital message to the PCM, which fires the low side of the relay to turn on the clutch.

You can check the clutch, but taking a wire and jumping the relay pins. If the clutch comes on the air gets cold, then you know you don't have a mechanical problem with the A/C system. Instead it's an electronic control problem.

If the HVAC control panel has a code, many times it won't allow the A/C clutch to fire. You need to resolve that code first which in this case means fixing the blend door problem. It could be the motor or it could be the HVAC control panel which seems to directly control the motor according to the schematic.
Hello and thank you gggplaya. I tested and my HVAC control panel does have a code, specifically DTC Code 4 - "An open or short in the mode control motor circuit." I do not have the technical skills to jump the A/C compressor relay (I can handle mechanical work but not electrical, not really experienced in that), so I am taking it to my local Honda dealer today for an A/C diagnostic (luckily they have a $75 special running, but still, oof). I hope to report back what the issue ends up being, and perform a replacement myself.
 

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Discussion Starter · #5 ·
Update, I brought the car in to my local Honda dealer for a A/C system diagnostic. The tech believes the A/C compressor needs to be replaced. I ended up ordering the FOUR SEASONS 4720NK kit from RockAuto because it has a 2-year warranty when properly installed. The warranty specifically states:

All compressors returned for defect must show proof of purchase of an A/C Orifice Tube (or A/C Expansion Valve), A/C Receiver Drier/Accumulator, and A/C System Flush or a Work Order showing the purchase of these items and that the system was flushed.

The kit comes with the A/C Expansion Valve and the A/C Receiver Drier, so I have that covered. Seems the only proper and legal way to empty the system will be to go to a shop, have them evacuate the refrigerant, then perform the part replacements myself, then bring it back to the shop to flush and refill the system. If anyone can confirm that's the correct order, I'd appreciate it.
 
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