SST Power Box Bench Test
When there is no air flow and the SST is turned on, it is normal operation for the green LED to come on for 10 seconds and then turn off. If this behavior exists with the blower running, then inspect the thermistor orifice for a clog.
The AFS uses a thermistor to sense air flow, see photo. The thermistor heats up to 120 degrees and when cooled with air flow, the circuitry switches the power on. The vacuum in the duct draws air through the orifice and cools the thermistor.
To bench test the power box, we use the setup shown below. Our fan draws a vacuum near the AFS orifice and we move the fan away until the green LED goes out. We compare this sensitivity to our test unit.
The most simple test is to just blow at the orifice with a straw. Use a mirror (shiny galvanized sheet metal) to watch the LED on the other side of the power box. The LED will turn on as soon as you blow, and go off with in a second after stopping. A hair dryer would also work.
A thermister is a device that changes resistance with temperature change.
Beware of electrical shock. The contact and rivets are live at 6200 volts.