T1 Terry wrote: This is a general type question. Is there any down sides to running a BLDC at slow speeds?
Two issues. To get the same power at lower speed, the motor will be running at lower voltage and higher current. Copper losses are proportional to the square of the current, so half speed means four times the copper loss. (You make up for it a bit with less iron loss, but probably not enough to compensate).
The other issue is that there could be a cooling fan attached to the rotor, so at half speed, you might get considerably less cooling. With the increased winding losses, you might get temperature problems.
However, I would assume that air conditioning is a moderately low duty application (say 60% duty cycle, total guess, on the hottest days), so it should have time to cool down.
I would say give it a try, but monitor the temperature. Maybe you can just glue on a temperature sensor and watch it from the cabin, or if it's accessible, use an IR thermometer to record temperatures after a commonly used route. If the case of the motor is below say 60C, maybe a little higher, that should be OK.
Ideally, you'd want a sensor on the windings, but you are most unlikely to be able to get to these inside an air conditioner, I would think.