Turning on Air Con blows fan relay fuse and turns off ventilation controls - Help!

I've recently had a problem with the ventilation and Air Conditioning (AC) controls failing, with none of the lights below any of the button selected lighting up. I replaced the 7.5A fan relay fuse in the bottom right of the fuse box below the dashboard, and all was well once more, but it failed again due to the fuse blowing after about 2-3 minutes of driving with the AC on. I tried another fuse, and as soon as I turned on AC, the new fuse blew. I think I could hear a click sound when it failed, presumably from a relay.

When it has failed, the fan still blows air, and I can adjust its speed and temperature with the two dials. AC wont work though, and the buttons will not adjust where the air will be blown. It stays permanently on the air direction that it was set on when it last failed. Losing AC is a serious problem for clearing the windscreen in winter, so am keen to get it fixed soon. But I fear that with quite a complex system, it could be time consuming for a garage to diagnose, so am hoping some of you can help.

Though it's probably unrelated, I do have a problem either with the wiring or more likely the ECU, which was repaired 3-4 years ago following burst capacitors, as I've recently been getting error codes for the TDC and no.1 cylinder sensors, yet have had both replaced recently to clear the problem, and I still get engine warning lights. Can't remember which was the latest error between the two. The car occasionally stalls on me, and occasionally stutters or just loses its spark and drops the revs down to zero. But it's not that bad, and runs fine most of the time, albeit with the engine warning light often coming on. Will probably just get a new ECU soon, but with a little beginning of rust underneath too, I fear this additional ventilation issue is making me consider my beloved's future a bit. If I can solve that, I can deal with the others I suspect. Though one thing I fear is buying a new ECU and finding that it was the wiring at fault, which would leave me with a brand new ECU needing selling, and no hope of fixing the wiring. But I'd hope I could find a buyer of the new ECU for a decent price if it came to that, particularly as I understand that the latest replacement ECUs are built with a lot more durability than the original.

Anyway, back to the ventilation issue. Firstly, it would be handy if anyone can advise whether there's any way the ECU is causing the ventilation issue, as its circuitry does interact with the AC. If I can solve both the AC *and* engine problems with a new ECU, then that would be great.

I've attached the translated wiring diagrams, with the most applicable being on page 6. I've also attached the heating system workshop manual which has a wiring diagram on page 15-6 which also shows the switches for the controls. I'm a bit confused, as the two diagrams don't really appear to be consistent, but maybe they show the same thing but from different perspectives. You can see the 7.5A fan relay fuse on both, and the AC system, but I can't quite figure it out.

Note that I wonder whether the AC system needs its gas or fluid replaced or topped up, as apart from a new belt, it hasn't had any maintenance for a decade or maybe two. Could this be the cause?

Attachment 2316Attachment 2317

Your most likely cause is a shorted A/C compressor coil.

Sheet one of the wiring diagram shows that 7.5A FAN RELAY fuse, its a direct feed for the compressor coil.

Theres a single wire connector on the compressor if you disconnect than and see if you can turn the system on and off with out blowing that fuse. (obviously the A/C wont be cold with it disconnected)

Its a fairly easy repair thou it does mean removing the AC compressor and stripping the outer clutch plates.

Item 16 is most likely the culprit (apart from a trapped wire or something like that)

38924-PJ7-S01 @ £101.64

Thanks Steve, when it comes to Beats, you're like Obi Wan Kenobi and Gandalf rolled into one. :D

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Originally Posted by Bruce

Thanks Steve, when it comes to Beats, you're like Obi Wan Kenobi and Gandalf rolled into one. :D

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Funny but true .

Attachment 2322Attachment 2321After installation of the Hayabusa, I had no AC. This was due to the sys was wired to the ECU, likely to allow a rpm rise when in use, or .. Anyway, if you want to temporarily remove the ECU from the sys, a short jumper wire is inserted between 2 wires (one is pink) leading into one of the three relays located on top of the RH wheelwell. I can take a pic and upload later today. The AC sys will work fine except at idle with the sys on, the rpm is slightly lower due to load of compressor.

Note the pink wire (to ECU) to jumped to the Blue/red wire. The AC sys will fully function.

you can check the resistance of the ac clutch coil, either at the ac compressor or at the underbonnet relay (the relay with the pink and red wires, disconnect the relay and check resistence of the red wire to earth)

Thanks for your help Steve, as always. Everything on my car is now sorted, pretty much.

I checked the resistance of the compressor coil, and suspected that it had shorted, so got it replaced, and the garage said that I had next to no gas left in the system, so I went to an extremely knowledgeable GoCool air con technician to get it refilled with a substitute for R12 gas called RS24 (which apparently doesn't necessitate modified parts being fitted for a full conversion to standard R134a gas). He checked for leaks and didn't find any, and was highly impressed that the air con still worked after 22 years (with virtually no maintenance to it for the last 9). However, we did find that another fuse had blown, for the condenser fan (it's one fuse down from the top right of the fuse box).

It's tricky to differentiate between cause and effect, and it might have been a lack of gas, but it's possible that the condenser fan fuse blowing caused the compressor coil to overheat, so I will keep an ear out to make sure the condenser fan periodically kicks in when AC is blowing - you can hear it run sometimes to the offside of the spare tyre at the front. I suggest other owners watch out for this too.

I also got the ECU replaced, and now no longer get an engine warning light, and the car now runs sweetly. However, on the way to pick up the ECU, sods law intervened and lit up the overheating exhaust sensor warning light, with the car running particularly badly. But with ECU in place, it runs great, albeit with this new exhaust warning light. But messages on this forum suggest that this light is nothing to worry about. I had I think the middle and final parts of the exhaust changed 2 years ago, so it should be OK. Mine is an older model which never had a catalytic converter fitted.

I wonder what to do with the old ECU - maybe I'll mount it on the wall... I've attached a photo comparing the old and new ones - there is quite a drastic difference in how much lighter both the case and the PCB is in colour, though I may prefer the green and gold tone of the old case. The car often ran fine with the old ECU in, once I figured out how to reset the ECU occasionally, but it did randomly suffer bad hair days. So if anyone wants to buy it at a heavy discount, please message me.

Thanks again,

Bruce

Attachment 2333

Glad you got your A/C sorted.

I would say that your old ECU problems are in the red highlighted area. Most likely blown/leaked capacitor, notice the staining on the board.

Yep, the capacitors had blown, but about 4 years ago I got them replaced and had bypass circuitry installed to jump over the parts of the PCB damaged by the capacitors' acid. The repair fixed the flickering warning light and problems with starting up the engine, and the car ran perfectly for over 2 years, but then my issues started with the no.1 cylinder and TDC sensors. When I got those replaced, I thought the persistent lights were an ignition timing issue, as you often suggest. But in this case, it was an unwell ECU. But compared to how the car ran before the old ECU repair, it's not been that bad really, particularly when it was having a good day. So my old ECU might still be of use to someone who can't afford a brand new one. Got the car through several MOTs for example.

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Originally Posted by Steve_M

Item 16 is most likely the culprit (apart from a trapped wire or something like that)

38924-PJ7-S01 @ £101.64

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Hoping this part is still available - any chance you can check stock in Japan?

Thanks,

Steve in Okinawa

Given that you're in Okinawa, can't you just pop by the dealership and ask?

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Originally Posted by 4Aaron GE

Given that you're in Okinawa, can't you just pop by the dealership and ask?

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Steve is more efficient than the people at the d'ship. Saving myself 45 minutes in a hot car too.


DOES ANYONE HAVE EXPERIENCE WITH REBUILT COMPRESSORS??

If the ones here are anything like the ones that NAPA could get back home, they do the job just fine. Granted, I couldn't tell you offhand which brand was the best (we tended to push OEM parts), but as long as you're not getting the cheapest available, you're usually going to be okay.

I did some poking around for that part number, and most E07A powered cars had it. It appears to be available here (https://www.amayama.com/en/search?q=38924-PJ7-S01), but if you're using yen, just pop by the dealer with the part number, grab a drink when offered, and enjoy the air conditioning. I know how painfully slow they can be (Honda is the only one I haven't been able to just waltz in and talk to someone in the parts department), but for a part like that one you can't quite get from Amazon, sometimes you just have to bite the bullet.

Conversely, if you want to chance a used unit, look for:

TODAY PRO
ACTY TRUCK
TODAY 3D
CITY
TODAY HUMMING
ACTY STREET
ACTY VAN
ACTY CRAWLER

(I cannot guarantee full accuracy of this list)

Thanks Aaron - I'll get it sorted tomorrow. Turns out I need new radiator too. Any thoughts on the aluminum ones for about Y11,000 on Yahoo.jp?

Steve

No experience with them, really. But for the money, it's worth a shot.

Who would guess that the same circuit that is fused for the a/c compressor also supplies main radiator fan relay? So if you lose a/c, you also lose system cooling? Not a brilliant plan IMHO, but it was a good test of my temporary radiator repair (JB-Weld).

I have a nice cold cockpit now but it cost!! The shorted compressor clutch caused the front gasket on the compressor to fail, so short story is that I had to get a whole new compressor installed. And surprise, surprise, all the a/c shops are stacked to the walls with work in midsummer, so I paid through the nose.

Steve in Okinawa