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

[Bruce]

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

[beecee]

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

Funny but true .

[marcair]

After 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.

[Steve_M]

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)

[Bruce]

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

[Steve_M]

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.

[Bruce]

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.