Same happens on the PCB - it gets warm. Told you it will happen This is exactly the reason why you should have four cables, not just two - high amperage will heat the wires/connectors.

If they shut down - what is the point of mining? Sure, the A/C will cool down the air eventually and ASICs will run again at some point. In this case the best option would be the chilled air flowing directly to the S3s and PSUs. Enclosing such heat makes it a hot air electric oven unless your A/C is more powerful than the S3s and PSUs combined (you can also think about throwing the PSUs outside the cold area if you don't care about cooling them).

That depends on the temperature of the air outside and the power of your A/C unit. 16 S3's generate roughly 16x the wattage of a single unit, say 350 Watts per unit. This is roughly 5.5kW (plus the power the PSUs take just for running, these generate some heat as well). Does you A/C unit have enough power to take this much load?
If not, they will fry - assuming you have them enclosed in that room. Done that with much larger server room, fortunately the devices survived.
If you don't have them enclosed, i.e. you let the outside air in and exhaust the "used air", having the A/C unit cool the intake air is actually more efficient than keeping it up in an enclosed cabin. Again, it depends on the power of the A/C unit.

Fully agree. If you are blowing the air outside the room, you have to blow some air in as well. In the winter it might be actually a good idea to have them cooled with the outside air - depends on your winter temperatures though.

Note that in terms of electricity bill - S3 takes X Watts of power, this converts to mostly heat (mostly being like 99% here). To cool the S3 you need an A/C unit that cools the X Watts produced, so the A/C unit should be able to take at least the same amount of electricity as the S3's combined. Ergo you electricity bill for the mining operation will simply double.

The point being here - you either
- seal the whole room, do not let the air in or out, cool it with a sufficient A/C unit, worry about it failing (fire hazard!) and pay double the electricity S3's take;
- let the air into the room, cool it down before it reaches the S3's, then let the S3 exhaust the air out - this would actually be the recommended solution for you since a) you don't have to worry about fire hazard in case the A/C fails (it is a wooden room, isn't it?), b) you don't need to have the A/C large enough (heat-wise) to take all the heat S3's produce (it will only cool the outside air a little) and c) you can leave the A/C off when the outside air temperature is relatively low (say below room temperature), during the cooler part of the year (again, depends where you live, though). This is not necessarily a cheaper solution (you still pay for the A/C working, but it does not have to be as powerful as in the sealed room conditions), but much safer, in case the A/C fails you do not give away the S3 produced heat in an enclosed compartment (an oven sould ring a bell) but rather blow the heat out cooling the units with (worst case scenario) outside temperature air.

Hope this helps...

Remember to apply a good thermal paste after you've cleaned the original one

The 4x cabling: seeing the paths on the board it look like both inputs are powering up exactly the same (i.e. this is not an additional board/unit, just a duplicate input) so I guess the "use 2 cables per hashing board" requirement is mostly due to possible cable/solder overheating due to high amperage.

Has anyone already tried sticking radiators to the R47 elements? does this do the same magic as it did in the S1's? (lower HW which seems to be the issue here)