Originally Posted by flatfour
The big NTC thermistor (SG379) is a 1 ohm inrush current limiter. The board that this part is located on is a DC power supply for the motor. It contains a full wave bridge rectifier and large filter caps. The Thermistor has a resistance of 1 ohm at room temp. As the motor starts to draw current, the thermistor heats up and the resistance goes down.
I have 2 furnaces in my house with the ECM motors. One of them burned the SG379 last week. I jumpered it wit a piece of wire until I get a chance to replace the part.
I am replacing mine with part number 495-2123-ND from Digikey dot com Cost was 6 bucks each plus $2 for first class mail.
The other blue discs on the board are MOV (Metal Oxide Varistors) They are the same component that are inside surge supressor power strips. They work by becoming a short circiut beyond a certain voltage. They "sacrifice" themselves to dissapate the surge. I do not have a part number for these.
As for the ebay guy, 100 bucks for a 6 dollar part is just wrong.
Thanks for adding this information to the thread. I can see that this is an ongoing source of rip off for consumers - $400 for a $10 circuit board and $1000 for a $100 motor, for instance. I am looking at a new furnace and I think I'll pass on the ECM motor, even though it would be an electricity saver.
I recently rebuilt my furnace's electronic air cleaner unit by just buying a few inexpensive new components from an electronic supply house. Fortunately the instruction manual had a schematic with all the component values listed.