I have an old carrier Weathermaker DX 58DXA060-100GG, and the blower motor has no oilers. I assume it was a replacement for the original. My question is, because I woke up to it humming and then it started but never shut off until the hi-limit switch was reset, can I put in a different motor? This is a 4 speed motor that is in it. However only 2 speeds are actually hooked up. Could a 2 or 3 speed be used instead? Also, it is a 1/3hp fla5.8 psc, can I use a 1/3hp fla6.1 or fla6.2, or even a 1/2hp fla6.1 or fla6.2? I don't want to spend the $250 for the exact replacement because I would be better off buying a new furnace. This furnace is about 25 years old from my diagnoses and investigation. I have replaced the spark control, the pilot and the inducer motor in the last 3 years. But if I keep replacing parts like this then it might just warranty a complete replacement. I have removed the motor and repacked the bearings with new grease, but it still has a slight moan on start up, but runs for now. I know it will quit again in the future.
I would replace the motor with a 4 speed PSC motor. Psc motors have more starting torque than non PSC motors and use less electricity to run and start, because they are more efficient. These motors are usually 4 speed however a few are 3 speed. you may want to check the capacitor since the motor will not run if the capacitor is bad and capacitors cost a lot less than a motor.
To find a different motor that will be the same size shaft and mounting you use the frame information on the nameplate of the motor, for an example: lets say a 145T motor will fit they come in many different configurations, 1hp, 1-1/2hp, 2nd. 2nd speeds normally ~1750 rpm or close and 3600 rpm then there are 2, 3,4 speed models. Last is the voltage all this information is on the name plate. If you only need 2 speeds it may be possible to find one that matches the rpm's you are after but the installer may have selected a 4 speed to get the best 2 speeds for your application.