It's obvious that you have problems with wiring. I would start from the heater/AC control panel.
the air conditioner and heater are two separate things.(not connected) ;) it may have a fuse. or the it could just be bad.
drain for the air conditioner heater case could be stopped up,or a heater core leaking... !!!!
its more than likely just low of freon.If it is a gm,most likely its your ac pump
I do not see how using the heater would effect MPG. The AC on the Prius is all electric, there is no compressor to put drag on the engine.
Heater core is leaking. Air Conditioner drain hose is plugged.
blower motors bad check fuse bore replacing
Refrigerator, radiator and air conditioner. Also, a stove, water heater and boiler.
Could be the heater. It's likely that most of the hoses to the rad were changed, but maybe a hose to a heater (if you have more than one), or the heater itself.
No. The problem is most likely your heater core. Ask a mechanic.
Assuming the heater works fine, you have a short, probably in the AC compressor clutch.
Take it back to the dealer. The AC drain is Blocked OR the Heater Core is Leaking.