Some will, most wont. The A/C button should, but the others you'll need to learn in the light and remember for night driving.
Usually take the car to the nearest Subaru dealer and have then fix it. They invented it, they should fix it.
The rear defroster (demister) on a Subaru Legacy is built into the window. The lines going across the back window are actually the defrosters. If the vehicle is equipped with a rear wiper, the switch for this should be located below the radio and heater controls.
The differential between the axles controls the AWD on a 1996 2.2 Subaru Legacy Wagon.
For the heater core. All cars have them.
It is a small brown one and is easiest to get to by pushing it out the firewall side and reaching up from underneath. It should have 6 pins. Mine was Jideco Japanese brand, but NAPA had a replacement.
check the fan relay, it could be stuck on, otherwise make sure the heater controls are not set to defrost, and the ac is off, either of these things will activate the auxiliary fan relay.
failed Heater core
The only bulb I can think of for an air conditioner is for the on/off indicator light. They use a special tiny tiny bulb only available through your Subaru dealer and you have to take the heater controls apart. This involves taking much of the console apart and the cables that come from the heater control tend to spring their clips loose and may cause the heater controls to stop working. If you can live with it not working that would be my advice. If you decide to change the bulb be prepared to spend at least an entire afternoon and keep the kids away if you don't want them to hear bad language.
the dome light fuse...any other questions
Heater inlet hose on a 99 subaru legacy is on the passenger side coming out of the fire wall. One of only 2 hoses coming out of the fire wall.
check your thermostat, if that isn't it you might need a new heater core. had one put in my f150 for about $150. With my car, it was Heater matrix clogged with radiator sealant. The workshop cleaned it and it's start working fine!
With difficulty. Tried to remove the one in my 1997 and found that you really do have to remove the entire dash to access it. If you have it out already, try to get your hands on a new heater box, saves the hassle.