1. Removed and sanded ground connections. Then checked for continuity back to house ground.
2. Checked flame sensor in series for 5 microamps. Reading never went above 0.3 microamps. However, while checking the amperage, the flame would ignite for only 8 sec. Prior to and after checking the sensor, the flame would ignite for around 30 sec before going out. If the sensor is disconnected, the flame will ignite for only 8 sec. The sensor seems to be working on some level. Odd though, acts like it's disconnected when the meter is hooked up in series. (Note: look at photo of meter to double check that I am using the correct settings - )
3. Checked the centrifugal switch. 1st test - jumped out the switch and got two flashes to signal the switch was stuck closed. 2nd test - disconnected the switch and got three flashes to signal the switch failed to close (stuck open). 3rd test - initially disconnected the switch, and after a few moments of run time, jumped out the switch. The unit operated like it had prior to test. Switch appears to operate properly.
4. Check upper and lower limit switches. Removed one wire from the limit switch. Each time, the board would signal four flashes for a limit switch that failed open.
Just in case it's helpful, here are the schematics that I have:
Schematic for old control board located on sheet metal cover:
Schematic for blend air switch:
Schematic for new control board:
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