Let's clear something up... Too many people get confused between thermocouples and flame sensors. Flame sensors don't use heat to generate a signal like a thermocouole does. Flame sensors use a process called flame rectification, rectification is the change from AC to DC. Ignition modules send an AC signal, which is usually 80v to 130v in my experience, out the flame sense terminal to the flame sensor. That AC signal passes through the flame to ground to complete the circuit. The flame acts as pathway to ground. This generates a pulsating DC signal that is read in micro amps. Next time you work with an ignition module, check the flame sensor terminal to ground while your meter is on VAC on a call for heat. It's best to remove the flame sensor from the module before doing this. #teachme

Posted by HVAC Know It All at 2021-11-26 17:08:50 UTC