HVAC Service Certification Practice Test 2025 – Complete Prep Guide for First-Year Exam

To test a hot surface ignitor (HSI), measuring resistance with power off is the recommended approach. When the power is off, you can safely use a multimeter to check the resistance across the terminals of the ignitor. A typical reading for a functioning HSI will generally fall within a specific resistance range; if it shows an open circuit (infinite resistance) or significantly different values than expected, the ignitor is likely faulty and should be replaced.

This method is effective because it determines whether the ignitor has the appropriate resistance to function correctly without the risk of electric shock. In contrast, other methods, such as measuring voltage with power on, can pose safety hazards and might not provide reliable troubleshooting data as the conditions during operation can vary. Additionally, applying voltage with the power off is not a valid testing method, as the ignitor remains inactive and does not reflect its true operational state. Checking for continuity while the unit is powered on can also be dangerous and may not yield accurate results concerning the performance of the ignitor.