At what reading is a cad cell considered to have failed during testing?

A cad cell, or cadmium sulfide cell, is a critical component in oil burner systems, as it detects the presence of a flame and controls the burner operation accordingly. During testing, a cad cell is typically expected to have a certain resistance range, which indicates its functionality.

When the resistance reading is above 1000 ohms, this indicates that the cad cell is not allowing enough current to pass through, signifying that it may not be detecting the flame effectively. This high resistance reading can be interpreted as a failure of the cad cell, meaning it probably is no longer responsive to light in the way it should be. Conversely, lower resistance readings suggest that the cad cell is functioning within an acceptable range, allowing it to detect the flame properly.

Understanding the operating range of a cad cell is essential for troubleshooting issues within a heating system. This knowledge helps in identifying whether a replacement of the cad cell is necessary or if other components of the system may be responsible for any operational failures.