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How to Test a Photocell: Spark Plug Style Heater
- Remove the photocell from the heater and connect an ohmmeter on the 1000 OHM(RX1k)scale.
- Hold the lens up to a light source like an 80 watt light bulb or direct sunlight, with the lens pointed toward the light. The resistnace of the meter should be low(less than 500ohms).
- Block off the light source by putting a thumb over the opening of the photocell. The resistance on the meter should be high. Replace if a change in resistance is not observed during the test.