This is a common cause of failure of the A/C on our civics.
In fact just a week ago Honda issued a Bulletin about it. The original fit Omron relay is suseptable to moisture ingress. This can form nitric acid in the presence of the normal arcing as the contacts operate. This will lead to corrosion and eventual failure. The Bulletin warns that the relay can fail either open or short circuit. If the latter this forces the compressor on to 100% duty cycle and can burn it out.
The remedy is a replacement relay from a different manufacturer - Mitsuba - that is a better quality item. The bulletin warns that the EPC is not yet updated, so you have to order this countermeasure part number directly to recieve the new part, otherwise you will just get the "old" part. I'm surprised they are not doing a campain over this considering if can fail in a way that might lead to screwing up other parts of your aircon
This the bulletin number:-
SM-10-002-00
It affects ALL civics (and CR-V and jazz) upto and including 2011 model year
Here is the countermeasure part number:-
39794-SDA-A05
RELAY ASSY., POWER (MICRO ISO) (MITSUBA)
The datasheet for the original Omron part is here:
The specific part is G8HL-H71 which appears to be a Honda specific version not listed on Omron's website - the standard relay is 180ohm and the Honda version is 120ohm coil resistance.
The Mitsuba part seems to already be used on other Hondas. I found this link for example
Hi Guys
I too am having problems with the AC, the cars been to Honda and they just re gassed the system which seemed to work for a few days (very hot weather those days) but soon after it started playing up.
I found that it would work for abit say 5-10 minutes then the air would be room temp rather than ice cold.
I found that flicking the AC button on and off loads of times would get it to kick back in but again some time later it would turn off.
Just ordered a new relay and Ill let you all know how i get on when it comes.
Some people have suggested leaving the old relay in and taking the car to a 'no work, no fee' type of service where if they top up the refrigerant and it doesnt improve operation, you get it free
I wouldnt suggest anything so abhorrently dishonest, but its a bloody brilliant scheme! If the AC system has been out of operation for any length of time or hasnt been recharged in a while, it can probably benefit from a recharge as the compressor shaft seal leaks at a very slow rate if the seal is not kept lubricated by regular running.
Ordered a relay off cox last night, I occasionally get a rough noise when on idle but only when the ac fans kick in (oddly if I dip my clutch pedal the noise disappears). Originally I thought it must be box related but if I switch the ac off during the noise the car sounds normal again and yesterday I noticed when the ac fans were running after a while I heard a loud humm, bit of googling pointed towards a possible faulty relay, I had a listen in the fuse box and heard a click when the fans came on, and noticed it's the naf branded sensor so hopefully this will cure it
Sorry for leaving this so long. I put the new relay in mine and its been working perfectly ever since. When i took the old relay out I could hear a rattling noise coming from inside so something has broken in there.
Good to hear, now keep your AC circuit from degassing over winter by giving it a 2 min run weekly to allow the oil to circulate and lubricatet the compressor driveshaft seal. Enjoy!
Right so I ordered the new updated Misuba a/c relay from cox Monday and received it the following day! So I removed the the old relay to see if that was a cause of the battery drain and I'm happy to report no dead battery of sluggish cranking. So it appears the old relay is at fault.
Now today I went fit the new one and I'm getting a CEL (I have been all week but I thought that was normal since I pulled the old relay out). It's B2991 or "DTC B2991 or DTC indicator F and AUTO: Climate Control Unit Lost Communication with Audio HVAC Subdisplay Unit (with audio system) or HVAC Subdisplay Unit (without audio system)" anyone have any idea what this means and how to rectify it?
I tried clearing the code by holding sel/reset for 10 seconds but it just reappears on start up! I thought all would be good after I replaced the relay. Would fitting the relay with the battery connected harm anything? Would the fact I've disconnected the HFT module affect anything?
Now today I went fit the new one and I'm getting a CEL (I have been all week but I thought that was normal since I pulled the old relay out). It's B2991 or "DTC B2991 or DTC indicator F and AUTO: Climate Control Unit Lost Communication with Audio HVAC Subdisplay Unit (with audio system) or HVAC Subdisplay Unit (without audio system)" anyone have any idea what this means and how to rectify it?
I tried clearing the code by holding sel/reset for 10 seconds but it just reappears on start up! I thought all would be good after I replaced the relay. Would fitting the relay with the battery connected harm anything? Would the fact I've disconnected the HFT module affect anything?
At a wild guess, sounds like the climate control unit has lost communication with the audio/HVAC subdisplay unit. In english, that means your AC controller isnt getting a signal to the black and white screen that shows your air temp and radio settings. Has that screen stopped working? If so it might mean its fuse has blown. I suspect the relay you've fitted wont have any implication on the working of this communication link, as it would likely be controlled directly from the AC controller.
Have you disconnected the handsfree about the same time you got the warning message up? I doubt it would be this either but as there is an indication of the handsfree being paired that displays on that screen there might be an obscure link between the two events.
Finally, its possible that you may have disturbed a connection in or near the engine fusebox which feeds into the AC controller. Not sure where on the car this controller is but I think it would very likely be found near to the engine fusebox.
Weird that removing the relay would cause that warning to appear, given that the relay should have no different an effect on the rest of the circuit whether failed or removed. Looking at your original message it sounds odd that the relay being duff would pull down the electrical system and cause it to drain the battery.
The only other thing I could suggest is disconnecting the battery for 20 mins to reset the ECU, might clear some internal error that's bringing up the alarm falsely. This might lose your radio presets but other than that it doesn't affect the car.
Tried resetting the ecu by d/c battery twice now already. 20 mins the first time around and an hour the second time round as I read somewhere a full hour is needed for a full reset.
I'm stumped too I'll reconnect the module when the mrs comes home from work but I'm stumped too!
Almost lost track of that nugget of info in everything else we tried earlier, why did you originally disconnect the HFT? Thinking about it, the disconnection could have an implication on signals the screen receives, which could in turn be causing an error in the screen controller, causing the HVAC controller to receive a fault signal from the screen.
Its far-fetched but it could be the culprit, stranger things have happened on this forum!
HFT was removed as I was troubleshooting the battery drain. A few people mentioned it can be a cause and since I don't use it anyway I thought it would be an easy place to start.
My battery died the other day and I took it to the dealer to have the. See what was wrong. They told me that the a/c relay was broken And that the a/c pressure com pressure release valve was also failing. Will I truly need to replace this second part or will replacing the relay fix the true problem.
Replacing the relay will solve your battery issue, but your AC system will not work unless both parts are replaced. The relay provides power to the AC compressor but if the relief valve is leaking then there soon won't be any refrigerant to pump and cool the cabin. Not a problem right now but come spring you're really gonna want your AC to be working properly!
Have you had the system recharged in the last year or two? It might be that whoever did it was a bit incompetent and overfilled the system, which would lead to the valve lifting, often once they lift because of an overpressure they never reseat properly with a full seal, it might have been leaking slightly for a while but without being able to run the compressor you'd not notice the slow degradation of performance.
as can be seen on this thread I changed the relay in my civic months ago and the air con has been faultless ever since. Now had my wife's 2007 CRV in for service at Honda last week, we told them air con not blowing cold air, they checked system and said all is fine? I noted on the original post from years ago that this relay issue included CRV, but can't see anything on here or the CRV subforum re the relay issue? anyone changed a relay in a CRV and had success? I am keen to try before giving back to Honda as it made such a difference to my civic that I am puzzled as to why they say our CRV has no issue when the air is just air, not cool at all most of the time now. Thanks
If you think it could be the relay and have a civic to hand with an updated relay, the first thing you could try should be obvious I can't see that Honda would use different parts for this common system so you'll likely find the civic relay fits into the CR-V, allowing you to test and confirm or discount it as a possible culprit without paying Honda for them to do exactly the same.
Changed the relay yesterday on my Civic just to be safe. The old one has been working ok all the time but you never know when so.
Mine had also something rattling inside the relaya and one starts to wonder how much the climate control electronics suffer when the resistor in the relay comes loose.
As the weather has been decidely colder since I had my civic I've not had chance to test my aircon. I did the aircon diagnostic and everything seemed ok. Since then I don't have the option of 'Hi' as a temperature setting, anyone else had this?
I've bought and fitted the relay and a new pollen filter as well, and will hopefully notice an improvement on how it's been to date. My OMRON relay had a purple felt pen line on it, any ideas what that might mean?
Sounds odd that you've lost the hi setting, how far does the temperature go up to now? What sort of driving are you doing, if its short trips in town then you might be draining your battery so much that the AC is self limiting to prevent you draining it all on heating. Alternatively it could indicate that your battery is losing capacity as it ages, I'm really not too sure on that one though.
The felt pen mark on the relay is probably nothing, maybe a quality assurance marking from the factory.
I do mainly long journeys. The highest setting I can get at the minute is 29, but I normally set it to 24 and let it auto manage, so not really too bothered.
Battery could be an issue, only just had the car and it looks quite an old one
Hi need your advice mate.. yesterday on my way home to braintree from heathrow my aircon just stoped working.. No air coming out of the vents so i told myself i will have it checked today but when i tried it this morning its working fine again. Do you think i need to change the relay and will fix the problem? This is the first time i encountered this problem.
No air, or no cold air? If its a lack of cold air then it might be the relay but that's not much of an issue while its so cold, and you'd probably not realise the difference anyway. If the ventilation stopped then that's very different especially if its restored itself now. I had a similar issue a few months ago where the vent suddenly stopped blowing but remained running, as though something was blocking the vent intake. Restored itself quickly and wasn't a problem ever again.
Is this what you experienced or did the ventilation stop completely?
Yes mate no cold air and i just figured out when im reversing there is a strange huming sound i thought it was just the front brake calipers locking. When relay is broken will the aircon not work at all?
No, when the relay coil fails you only lose the cooling provided by the refrigerant compressor, the ventilation and heating functions are completely unaffected. Its possible your compressor clutch might be slipping but I'd be surprised to hear it doing so in such cold weather - normally it would have to be very much warmer to bring that on.
What temperature do you think you're getting out of the vents, around room temp 20-21, or higher? You're unlikely to find out whether the AC compressor has failed in such cold weather as the air temperature coming into the car will not need to be cooled very much by the refrigerant, it being so cold already.
An easy tell tale is: once you've been for a drive of at least 20-30 mins with the vent on auto and fan turned up to high speed, then park on a slope and see if you get a trickle of condensation running out from under the engine bay (behind the passenger side tyre) after a while. Condensation is a natural run off of the water vapour the cooling circuit removes from air before it enters the cabin, it flies off the condenser at any speed but once you park up any remaining condensate ends up trickling out from behind that tyre as though the car has wee'd itself.
If you get this trickle, the AC is working just fine, and your problem rests elsewhere.
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