AC system/heating system. The only good part in this whole system from what I can tell would be the heater core. Everything else has had to be "fixed" and or replaced. I say "fixed" because the dealer (Performance Toyota of Lincoln NE) are a bunch of hammer mechanics who ruined the AC in this vehicle by converting it to the newer refrigerant. But this was okay because I had already written the thing off as junk at this point anyway. They stole my $800 to "fix" the condenser because it had a major break in it and I had to "eject" from the vehicle because the passenger compartment filled up with freon. I could not see and I was lucky I was not going 55 mph down the highway in traffic. They ruined the compressor in the process of "fixing" it although I'm sure they would deny they did this. They tried to fix it 4 times but it kept leaking down. Heating system controls are shot, speed control replaced, rheostat replaced, fan blower replaced, AC switch shot, AC idle ramp up switch shot/replaced, AC leaks, compressor shot, thermostat sticks, radiator no good, just to name only a few problems in the heating/AC system, this would scratch the surface I guess.