So when I bought my house several years ago it was serving as the development's model home with an office built into the garage. We had them convert the garage back into a garage, as part of which they 'unhooked' the ductless HVAC unit mounted on the garage wall. I use quotes as their unhooking amounted to pulling the wires out of the distribution box and physically cutting the cable going from the external AC unit to the wall unit. I never bothered about it because I didn't have any especial need to have AC in my garage.
Well, now I have a large furry dog who abhors crates and can't be trusted to run around loose indoors alone all day. It promises to be a very hot summer, so I figure some AC would make his life more pleasant on very hot days. Problem is, I have never wired anything into mains power before and I don't want to die.
The power supply cables attached to the external unit contain wires which are distressingly indistinguishable from one another but I have an ohmmeter on hand so I can presumably figure out which is which and hooking the external unit to the internal unit looks straight-forward. I've built electronics before so I'm not worried about the technicalities or reading the diagrams. But I've never done anything with one-phase power at housing voltages.
So we come to the crux of my question(s):
The power distribution box on the side of my house. It has 4 posts plus a ground post. There are 4 wires coming into it from...wherever the house mains wiring is coming from. A bare ground wire, a black wire, a white wire, and a red wire. My intuition would expect the red wire to be hot and the black to be neutral. Dunno what the white wire would be.
The red wire is just capped and not attached to anything. The black and white wires are connected to the two posts labeled LINE. Nothing is connected to the posts labeled LOAD. This leaves me wondering what the red wire is for. Perhaps there are two hot wires for when one wants 220V?
The AC unit requires a ground connection and two power connections, labeled L and N in the diagram. It's my understanding that the L here is 'Live' and the N is 'Neutral', so once I figure out whether the white or black wire is hot (presumably the white?) I guess I connect the appropriate wire to the LOAD post beside the appropriate LINE post?
I'm further given to understand that it is standard practice to determine your hot wire using a contactless voltage probe. I don't have one, but I do have a multimeter. Am I going to explode myself (or at least kill my meter) if I attempt to measure voltage on the wire(s)?
Photo of the distribution box in question: