GUYS!!! I solved the mystery that has been plaguing my FAN-PWM V3 install every since I first started using this Spal controller!
In fact, I had this same problem with a previous SPAL controller and I replaced it, and the problem was there with the new one as well! Well, now I know why... Because it's a damn design flaw! <img src="/forums/images/graemlins/angry.gif" alt="" />
In case you didn't read my story, what was happening was sometimes the controller would blink a code and not turn on the fans. The code it would blink was either "fan not found" or "over-current detected", or sometimes both. Then the fan wouldn't turn on.
Here's the deal. The FAN-PWM V3 has 3 power transistors inside that it uses to switch the power on and off rapidly to the fans (aka PWM). It does this for "low" mode. These power transistors get hot so they need heat sinking to something that can dissipate the heat. The chassis of the unit acts as the heatsink. There is a pad of supposedly non-conductive thermal material sandwiched between the transistors and the metal housing of the unit. Then there's a piece of thin springy steel that pushes the transistors against this pad. So there should be a firm connection there allowing heat to be effectively dissipated.
Now, these transistors have some metal on them, and it turns out that this metal, which touches the thermal pad, carries positive voltage. When the fan is off you'll see 12V here, and when the fan is on low you'll see around 4 to 6 volts here. If you were to, say, short this to ground, it would turn the fans on, and current would flow through your short, into the fans. But you DON'T want that...
Unfortunately, over time the thermal pad wears away and the metal part of these power transistors ends up touching the aluminum housing of the FAN-PWM V3. Now, most people are probably inclined to mount this metal housing of the FAN-PWM to their chassis. If you do that, you end up creating a grounding path from your car's chassis, to the FAN-PWM chassis, through worn out thermal pad area, and into the power transistors, thus turning on the fans.
So a couple things can happen. In my case, the connection between my car's body and the FAN-PWM housing wasn't very solid, so it would only ground out sometimes. What would happen is the fan would be on Low, and then the chassis would ground out, sending more current through to the fans (running them full speed), which would confuse the hell out of the controller and it would say ERROR! Too much current detected!
The other thing that could happen is if it grounds out while your vehicle is turned off, I think it can actually make the fan run, and kill your battery! I am pretty sure this has happened to me as well.
So, I think I can fix it. I ordered some Arctic Alumina Thermal Adhesive. It's great stuff, I have worked with it before. It's basically a 2 part epoxy that transfers heat really well. The nice thing about this particular stuff is it does NOT conduct electricity, only heat.
The fix I'm going to try:
Disassemble the unit
Paint on a layer of Arctic Alumina
Put on a 2nd layer to glue the power transistors down
That should fix it <img src="/forums/images/graemlins/notooth.gif" alt="" /> I'll report back.