Few Queries:
1. Are you using Arduino UNO?
2. What is the resolution in bit of your ADC?
3. Is the ADC unipolr or bipolr?
4. What is the FS of your ADC?
5. What is the VREF voltage of your ADC?
6. What is the ADC value for temperature T10C (say, 250C)?
7. What the ADC value for temperature T20C (say, 400C)?
8. What is the ADC value for temperature T30 (say, -100C)?
9. What is the type no. of your temperature sensor? Do you have any idea about its response curve?