Nissan Repair: heater, temperature gauge, heater core

Question
MY car dosen't blow hot air.  It blows cold air all the time.  At 75 degrees, it is barely blowing  hot air.  Do you have any idea what's wrong with it.  
Thanks.  

Answer
Raven,

Change the thermostat if the temperature gauge does not read where it should.  That is, half way or a bit lower on the gauge.  Other causes of the heater not working is the heater core is plugged up.  If someone used stop leak it can plug the heater core.  Also, if the blend door is broken it will not allow heat to enter the car.  Check it out and email me back if you have further questions.