The Weather Eye is a trade name for the patented Nash Motors-designed fresh-air automotive heating system first used in 1938. This "Conditioned Air System" is characterized by a cowl-mounted outside air receiver that then passes fresh air through a heater core utilizing hot engine coolant for a heat source. In 1939, Nash added a thermostat to its Conditioned Air System, and thus the famous Nash heater was first marketed. The use of the Weather Eye name for automobile heating and air conditioning systems continued in American Motors (AMC) vehicles.
The famed "Weather Eye" was developed concurrently with the much lesser-known but contemporary Hupmobile Evanair-Conditioner that took its fresh air through special hood scoops. The principles of both the Hupmobile Evanair-Conditioner and the Nash Weather Eye are still in use today in nearly every motor vehicle.