no heat

i have a 1995 millenia L no heat, but the air conditioner does work. the only thing that i notice is that the temp gauge is kind of hot but the car is running just fine. last time the mechanic checked it he said that their is no air in the sytem but it seemed that the temp sensor was bad. my question is what is causing the car not to have heat? their r no leaks.

Your heater core is probably clogged. Take off the two heater hoses and run water from a garden hose through it until it comes out clear. Then I would flush the rest of the system to make sure theres not gunky crap elsewhere in the coolant path. This might also cure the overheating.

The obvious could be low coolant level as this would explain the somewhat hot running level and lack of heat. Also, it could be the thermostat. I too have a 95 and had to replace it. I have found that at idling, little heat comes out (lots of air, but little heat)... as soon as engine speeds up, heat is much better. I believe the water pump is tied to the timing belt, so try reving motor slightly to see if heat improves.