Gas Fitter Practice Test

On a high efficiency furnace, what turns on the blower fan?

1. Klixon limit

2. Bi-metal switch

3. Relay timer

4. Temperature

The correct answer is: Relay timer

In a high-efficiency furnace, the blower fan is typically activated by a relay timer. This component is crucial for ensuring that the blower operates at the right moments during the heating cycle. Once the furnace reaches a predetermined temperature during operation, the relay timer sends a signal to the blower fan to turn it on, allowing for effective circulation of heated air throughout the space. This process helps in maintaining a consistent temperature and improves overall heating efficiency. The relay timer ensures that the blower does not operate immediately but rather waits until the heat exchanger has warmed sufficiently, preventing cold air from being blown into the living area initially. This sequential operation enhances user comfort and energy efficiency. Other components, such as limit switches or bi-metal switches, often play roles in safety or control but not directly in activating the blower fan in this context.