FAA Powerplant Written Practice Test

When does refrigeration icing occur in carburetors?

1. When fuel vaporizes in low temperatures

2. When humidity surrounding the fuel freezes

3. When air pressure drops significantly

4. When the ambient temperature rises

The correct answer is: When humidity surrounding the fuel freezes

Refrigeration icing in carburetors primarily occurs when humidity surrounding the fuel freezes. As fuel is drawn into the carburetor, it undergoes a process of vaporization, which absorbs heat from the surrounding air and can lead to a drop in temperature. If the humidity in the air surrounding the carburetor is high enough, the moisture can condense and freeze, forming ice. This phenomenon affects the flow of air and fuel mixture, potentially leading to engine performance issues. While other scenarios, such as low temperatures causing fuel to vaporize, do contribute to carburetor performance changes, they do not specifically relate to the formation of icing. The same applies to significant drops in air pressure or increases in ambient temperature, both of which may affect fuel-air mixture conditions but do not induce refrigeration icing directly as described in the context of carburetor operations.