If you are blowing cold air, it probably not a temperature sensor problem. Was the thermostat put in right - side - up??? Also, the sensor wire could have possibly broken or come unplugged while you were installing the new thermostat. And there are only a couple of reasons your only getting cold air now and that is (a) you installed the thermostat wrong or(b) the new one is defective. Remember to replace the coolant. Sounds simple but too many forget too.
It could also be that the small plunger, just to to the left of the spark plugs/toward the back of the engine, is just stuck. Had this happen many years ago. Pull on it and then spray it with lubricant.