no heat on 1996 Chevrolet Cavalier

i have no heat when gets cold i think the fan stays on all the time is there a sensor?

It could be a faulty coolant temperature sensor or a bad fan relay is always on because the car does not know the current temperature of the vehicle for safety is always on to prevent overheating i would get a diagnostic to see if you have any codes if not i would check the fan relay. No heating i would check the thermostat.