The furnace is a Carrier (FXM4X4200AT)
it has a 1/2 hp blower motor (KMSAHO13C02): Zhongshan Broad-Ocean ECM Motor
The motor was running with irregular speed that goes up and down at constant frequency.
Also the motor keeps running even if I unplug the speed cable low voltage.
The power supply are correct 240v (black + Yellow) and the low voltage 24v between Brown and Blue.
I bought a replacement motor and installed it. The new one runs at constant but low speed disregard of speed connections 1 to 5 I use and also the motor still keeps running even if I unplug the speed cable low voltage.
Any suggestion about what might be causing this behavior? Thanks
So you replaced the motor only? Not the ECM that attaches to the motor? Or did you buy a completely new motor and ECM as one unit?