Vp Climate control ac fan relay wiring help needed

[VTXU8]

Yeah, you're right. The is a slight difference. The rear demister is controlled by the bcm if fitted. All the switching/coms for A/C(including cooling fans) with/without climate control and bcm is done by the ECU. That's the common denominator. So hopefully it's not the ecu. The climate control module only communicates with the ecu.
I would still check the "warning lamp check relay" as it's the same with/without bcm.

Check voltages on ignition relay and see if you have 12v between 85 and 86 and see if pin 30 has 12v (which you've probably already checked multiple times) If pin 87 has 2.5v with ign. off then I would suspect that fuse #17 will also have 2.5v...
Try just running ac without cooling fan plugged in(won't hurt running for a minute or 2) and see if problem goes away.

[vp304]

So down where my car is now
Fuse 9 removed the the AC cooling fan relay removed I get 2.5v on one side of the fuse 9 connections other side is zero v.

Pin 87 of ignition relay base with relay removed also has 2.5v with ignition of.

Car is LS1 ecu with ls swap so I'm using the old ac fan relay to trigger my FG thermo fan hi speed. Will check out the other bits you told me to check now also.

Don't know what can be causing this tho I have a switch in cabin to supply negative to that ac fan relay if I want to run the fan manually. With the switch off is 2.5v on fuse 9 with ignition off.

With the fan bypass switch switched it causes the positive voltage on fuse 9 to go down to like .2v

Pin 85 and 86 on the ignition relay gets 12v when I ignition on and off but is working at the moment. Is tempramental this thing. The 2.5v on fuse 9 is not right tho maybe causing my issue.

Maybe I've stuffed something up somewhere along the line and mixed 2 circuits maybe some kinda feed back or something

[vp304]

Just had a look at that diagram your right that lamp check relay does supply the ignition relay. Maybe when car gets hot that relay is in engine bay and playing up

[brindo]

Silly question but there is a 5 pin relay in the engine check lamp, not the 4 pin?

[vp304]

Hey brindo yes is a factory bosh metal top 5 pin relay in the lamp check location in engine bay

[vlad01]

I've had that relay play up and it stops all AC, blower function and HVAC related items as well as the radiator fan, it nearly overheated my engine on my restro car, and I suspect was the reason my first VP overheated and seized (fan stopped in peak traffic on a 1 or so Km long suspended off ramp with no emergency lanes to stop in) fan started working and I never had a re-occurrence for the rest of the car's life. I always though the ECU was at blame as I replaced it just in case and never had it happen again, but it started working even before I did that, but the restro car was a once off as well, found the fault after tracing every wire, eventually back to that relay and it clicked back to life as soon as I moved it in it's socket, I changed the relay anyway and made sure the socket was clean and lubed against corrosion.

Kinda scary that one relay can doom your engine.

[vp304]

Hey vlad01 thanks for the bit of info looks like i might not be the only one with this weird issue

[vlad01]

Yep, now that I know about it, I cleaned and sprayed the sockets and made sure the relay clicks on and off. I suspect the sockets oxidizing are the main cause. I had a VN wagon I did tuning for a friend, and I found half the sockets corroded and at least 2 relays didn't work that I recall and came good after a clean and re-seat. And at least 50% of the terminals in the fuse panel under the dash disintegrated, the oxide makes the brass brittle and they just shatter like old plastic. In this case, the car showed evidence of extremely high moisture/humidity in the cabin, every plated or otherwise metal surface looked like it had been out in a paddock out in the weather. So the car probably was left outside with a window missing or similar, leak etc... So the brass terminals were totally F'd because of the metallurgical changes they had gone though. You can actually buy ther terminals and even the fuse panel brand new now, from Rares and Holdcomm I'm pretty sure.

Some possible causes summarised here by google.

https://www.google.com/search?q=embitle ... s-wiz-serp

Also the fuses even in healthy cars get this granular crystalized texture, like a hard dull gritty rock like coating, it doesn't look like oxide alone, but something like micro crystals, maybe some form of tin whiskers.

This adds a ton of point contact resistance, and along with potential for the terminals to go to shit as well, but even in good cases where the terminals are good, the fuses aren't and this added resistance causes the contact points to heat up, this then starts the oxidation of the heated area, further increasing resistance, then it heats even more and the cycles goes runaway, the fuse sockets then proceed to melt and catch fire. The sockets on the fuse panel are now at the age where burning out spontaneously due to that process is becoming common. So do yourself a favor, check them out, clean them if needed, lube them with a very light corrosion inhibiting spray, I use Rem oil for guns as it drys with almost no oily residue and has an anti corrosion chemicals in it. It's worked well for everything I use other than a pure lubricant. And lastly, replace every single fuse! It will replace the bad tin plating with new that will ensure the contacts remain at a low resistance.

Do the same for the ones under the bonnet, the headlight ones especially as they are high current ones and will likely go first, mine did on the shitbox before anything else ever did and did at night where I couldn't even see anything when they went out.

The relays can and do corrode on the pins too, but they are usually brass and don't have a tin plating, they can just be cleaned to take the tarnish off a little. But it's always a good idea to replace them with good quality genuine Bosch ones. I know on my nephews V6 converted 4Runner, all the aftermarket relays were dead shortly after the conversion it seems and some stupid mechanic or auto elect couldn't figure that out and wired in new relays elsewhere or in the case of the rad fan, added an external electronic thermostat switch because I guess they thought the ECU wasn't switching the relay, but it was the relay itself that died, 100% of them died, so I tossed them and put used Bosch ones and they worked fine. But at this age, new quality relays is probably a good idea. Even if the contacts aren't worn, the mechanics in them can age in the form of weak springs, sagging of parts that are under tension etc... and just general oxide and wear elsewhere over time.