I noticed a duct leading into the back of the ECU box, and surmise it is for cooling. This thread describes the system somewhat, but leaves me with questions. As the ECU itself is a pricey item, prone to failure if it overheats, disabling the car if it fails, the cooling of this box seems of non-trivial importance. And yet, in my car the cooling seems likely inadequate.
I observe that air comes into the ECU box from a duct that connects with the firewall. The flow of air into the ECU box correlates with the HVAC fan setting in the passenger compartment. If that is set to high/max, then it feels like some air is being pushed into the ECU box. But if the cabin HVAC fan is set to zero (i.e. off), as it might be on a warm day, driving around with the windows open, then no air flows into the ECU box.
In the thread referenced above, a fan is described (and shown) that sits at the point where air enters the ECU box, and that would force air into the box. My car does not have such a fan, nor any apparent supporting infrastructure – left-over wiring/connector, or even enough room to place a fan – and yet my car’s bits and pieces there seem complete. Thus my first question: did the 2001 V70 T5 come with a dedicated little fan that forces air into the ECU module box?
A lesser of my question is related to venting the ECU box. If air is forced in through one opening, then the box needs another opening to allow air to escape. In my car, that appears to be a duct coming off the bottom front of the box, leading down to somewhere near the bottom of the front right fender or bumper area. The cover of the ECU box shows a vestigial duct structure at the top of the box facing forwards, but it is closed off. Elsewhere I read that in older cars this would have some ducting coming off it, going down somewhere (called by some a snorkel).
Now we all know warm air rises, so this begs the question: why wouldn’t you want to have the venting happen at the top of the box? (…for either of the duct configurations I’ve described). Why would you have the ducting go down. It seems to me you’d never be able to get rid of the hot air in the ECU box, as it would just accumulate at the top of the box. But I have a theory… is it possible that at the bottom of the “exhaust” duct, at the bottom of the car, air is drawn out of the duct by the Bernoulli effect? That when the car is moving, the air flowing laterally past the exhaust duct opening actively draws air out of the duct, thus out of the ECU box?
Even if the exhaust duct design is actually to work like this, why connect it to the bottom of the ECU box?? It would make lots more sense to connect it to the top of the box, as it apparently was in earlier years. Where can I find an exhaust duct for the earlier years? (part number?) Some have called it a “snorkel” tube.
Greetings from VA.
Boris