Most of the time when the cfm fails it's not running when I arrive and the repair is simple enough. Sometimes though the unit has been shut off and I can hope it fails while I'm there or get an amp meter reading high enough to indicate failure is imminent. So the question is there a percentage of rated amps that above which you can consider the motor faulty?
I've been amping the new ones after install and they run real close to 68% of what's on the motor plate. I had one that was running at .9 amps and the plate stated 1.1 amps, which is 82%. This motor failed while I was standing there after it had been running about 20 minutes. Amps shot up to 2.6 and it screached to a halt.
I know this is a broad question concerning different mfg.'s but since the motors are all made pretty much the same way they should fail about the same way.