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Premium Member
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120 Posts
Discussion Starter #1
Hi

Just a quick question - the OH was out in the car last night and reported that the heater wasn't working. Tried it this morning and it seemed fine - for about 2 minutes - and then it shut itself off.

I noticed that the motor sounded a little noisy, but other than that it seemed fine - I was able to change the fan speed and adjust which vents were getting air whilst it was working.

Obviously as it was working, then not working, then working again, then not working agiain, I've ruled out the fuse and am assuming it's some sort of self-protecting behaviour? I've not checked the filter but it's no more than 12 months old. It's a pain to check because the little clip that holds the cover on has was snapped when I got the car, so the cover is taped on.

My initial suspicion is that it's the motor noise that's the clue - although it was no more than 'a bit of a whine' rather than sounding like it was on it's last legs. I understand that access involves taking the clutch pedal off (is that for RHD cars?) and a fair bit of disassembly, so before I do that I'd like to be more certain as to what the actual fault it - so, if I take it to the garage, is there any chance any more detail will come up on the scanner (not keen on paying for a diagnosis if nothing is going to show)

Any other avenues to investigate much appreciated. Of course it's packed up just as it's getting cold!
 

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Discussion Starter #3 (Edited)
Thank you! This is why I love forums - I read all that when I got my first Civic and had forgotten all about it!

I did the first diagnostic test first as that seemed the most sensible one to start with :)

Ignition OFF / Press and hold down the A/C system's Auto and Mode buttons / Start the engine / Release the buttons

All the readings seemed sensible except for

9th sensor: vent output air temperature C which the car seemed to think was 38 degrees - which would seem unlikely given that it as 9 degrees outside and the car hasn't moved for 9 hours.

While is was in reading 9 the fan came on fully as well.


With the other test - Ignition OFF / Press and hold down the Auto and Re-circulation buttons / Ignition into II position / Release the buttons

I just got 88 88 which alternated with a single segment (the lower right hand edge of the last 8 iyswim)

So it looks like it might be something to do with a rogue reading from vent output temperature sensor? Does that sound like it would trip the system to off? I know where the cabin temperature sensor is, but I have no idea where the vent one is - any info would be much appreciated.

Thanks again.

UPDATE - I thought I'd go and make a note of the other sensor readings for the sake of completeness:-
1st sensor: Cabin temperature C - 12
2nd sensor: Exterior temperature C - 10
3rd sensor: Solar radiation sensor value (Dark=00, Flashlight=04, Cloudy=10, Sunny=65) 1 (night, but parked near a streetlight)
4th sensor: Temperature of the air exiting the air conditioning evaporator C - 5
5th sensor: Drivers air mix opening (low value indicates cooler air distribution, higher value indicates warmer air distribution) % open - FO (fully open?)
6th sensor: Passenger air mix opening (low value indicates cooler air distribution, higher value indicates warmer air distribution) % open - FO (fully open?)
7th sensor: Mode positioning % open - 26
8th sensor: recirc flap % open - 00
9th sensor: vent output air temperature C - 75 this time

On the second test it just did 88 88 and then nothing - although the fan continued to work while I was in the car for a few minutes.

As a further update, OH said the heater was on for about 5 minutes this morning and the fan was going at full speed all the time - but that might be because I had set it to full speed manually when I was messing with it the other night and she hadn't noticed it wasn't on Auto.
 

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432 Posts
Looks like the vent sensor is going faulty. I had the cabin temp sensor fail intermittently which causes similar issues. I will have a look in the Haynes and see if I can find a location for you.
 

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Discussion Starter #5
That would be awesome if you could - thanks.

Apologies for the late reply - I've been moving house so I've been quite busy and without internet.
 

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Discussion Starter #7
A belated thanks very much for this - house move has been utter chaos so I've not been online much. Fortunately the car has behaved perfectly since the few incidents when I first posted, so touch wood it was some sort of temporary software-glitch or a stuck bit of leaf somewhere or something.

(and please don't let it fail again when it's properly cold!)
 

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Registered
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Put the heating system into diagnostic mode when its not blowing and post the results. Instructions are in the wiki at https://www.civinfo.com/wiki/index.php/Climate_Control

In particular, what temperature is the cabin temperature sensor saying.
Can you please send this link again because it doesn't work.
Northern Soul, did you fix this problem with the blower?
I have the same and already replaced flap motor actuator and the heater blower motor fan from other car but it doesn't work again - when I start the car and press the button it starts only for 5 seconds (I hear the compressor) and then stops without blowing hot or cold...
 

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Premium Member
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Can you do me a favour please? Remove the aircon relay from the under bonnet fuse box and leave the car overnight. Then see if the heater works normally the next day and report back.

There are 2 diagnostic tests which I have listed below

Sensor check

Ignition OFF
Press and hold down the A/C system's Auto and Mode buttons.
Start the engine
Release the buttons
On the A/C - Radio display you'll see the sensor number and the value for that sensor.

Press the heated mirror button to advance to next sensor
1st sensor:*Cabin temperature*C
2nd sensor: Exterior temperature C
3rd sensor: Solar radiation sensor value
4th sensor: Temperature of the air exiting the*air*conditioning*evaporator C
5th sensor: Drivers air mix opening
6th sensor: Passenger air mix opening
7th sensor: Mode positioning*% open
8th sensor: recirc flap*% open
9th sensor: vent output air temperature C

To check for HVAC fault codes

1. Turn the ignition switch OFF.
2. Press and hold the recirculation control and rear window defogger buttons, and turn the ignition switch ON (II).
3. Recirculation indicator turns on for 2 seconds, then self-diagnostic function begins.

NOTE:
•The blower motor will run at any speed during the self-test regardless of the dial positioning.
•In the case of multiple problems, the recirculation indicator will blink the lowest number DTC only.
•If no DTCs are found, the indicator will not blink. DTC (Recirculation Indicator Blinks) Detection Item
Error codes are below

1 An open in the air mix control motor circuit
2 A short in the air mix control motor circuit
3 A problem in the air mix control linkage, door, or motor
4 An open or short in the mode control motor circuit
5 A problem in the mode control linkage, doors, or motor
6 A problem in the blower motor circuit
7 HVAC control unit internal error
8 An open in the evaporator temperature sensor circuit
9 A short in the evaporator temperature sensor circuit
 

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Discussion Starter #11
Obviously the car isn't seeing much use at the moment, but immediately prior to the lockdown the heater was not working at all. However, if you kicked the resistor pack near the clutch pedal a bit, it would come on. Sometimes it would stay on - but not often.

Today I finally had a go at getting it out. If it helps anyone else, it's just to the left of the clutch pedal on RHD cars, and is held in with two screws, one of which you can get a screwdriver on, and one you can't unless you want to start removing bits of centre console. The screws are those ones where the head is also hex shaped though, so if you have a small ratchet handle and a short extension you can get the other one out - it's 8mm I think (I used an imperial one that was a good enough fit because I couldn't find all my metric ones - I've left it in the car for when I refit and can't be bothered going to check - this is probably the sort of behaviour that explains why I can't find all the sockets:) I reckon it's also possible with one of those right-angled screwdrivers like an allen key, but as you can't see the head very easily at all, it'd be a pain every time you had to refit the screwdriver, which you will have to do a lot because you won't be able to turn it much.

A few of the solder joints on it looked scorched, so I'm going to clean and re-solder them and see if it works. Will keep you posted.
 

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Super Moderator
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2,355 Posts
the resistor unit does come out by just removing 2 screws easily without removing centre console
I have a spare somewhere
they can be repaired by a company near me ill try find details if it helps
I had similar issue on my 8g few years back but it turned out to be the blower motor
now that's a bit more fidly to change not impossible but needs a bit of patience
and helps if your double jointed
if you don't change the cabin filter it can put more load on the resistor
 

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Discussion Starter #13
Agree it's just two screws, but you definitely can't get a normal screwdriver on to one of them - but yes, you don't need to get the console out, and once it ad occurred to me that I could use the ratchet it took about 2 minutes.

Hopefully it is the resistor - it definitely turns the fan on and off id you wiggle it just so. And inside it looks like this. Hopefully get a chance to have a go at cleaning it up later and see what happens. Otherwise I think I'll send it to this place - Honda Civic VII VIII Heater Blower Problem, Fixed In Minutes

312899
 

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i-Vtec
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3,272 Posts
A tip to stop the resistor getting fried is to keep the fan on a higher blower speed. The resistor pack works by throttling back the voltage at lower speeds, this in turn causes heat, the slower the fan speed the higher the heat in the pack the more chance of it overheating and frying itself.
 

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Discussion Starter #15
A tip to stop the resistor getting fried is to keep the fan on a higher blower speed. The resistor pack works by throttling back the voltage at lower speeds, this in turn causes heat, the slower the fan speed the higher the heat in the pack the more chance of it overheating and frying itself.
I pretty much always leave it on Auto to be honest - so I suppose for half the year it's on a pretty slow speed a lot of the time.
 

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Discussion Starter #16
In case any one else has this issue, I can report that a replacement resistor pack fixed it. I couldn't de-solder mine because my soldering iron is too weedy - the solder is quite thick and I was just heating up the whole thing rather than melting the solder. It needs a higher powered soldering iron so it can heat the solder faster than the solder can dissipate the heat into the surrounding parts.

I was going to send it off to be repaired but because of COVID the place I found is shut, so I looked for a replacement part, and found one on ebay for £15 - it's part number 79330-S6M-941. The one I found didn't list the Civic as being compatible in the eBay drop down checker thing, but it arrived today, it's the same part, and it works perfectly. Perfect timing as it was quite hot today and I had to use the car.
 
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