My air handler requires a clock wise rotation of the fan motor. After installing a new motor I found it was set in the counter clockwise position. I changed the wires (switched inline connection on fan wiring) for a clockwise rotation and found a great reduction of RPMs compared to those of the counter clockwise rotation. Why would the RPMs drop and how would you resolve the problem and regain the lost RPMs?
The wiring diagram isn't available but the 1/4 hp motor is reversible: yellow connected to brown with orange to purple being clockwise and yellow connected to purple with orange to brown producing counter clockwise rotation. Yellow is the common and is connected to power with a choice of Black wire for Hi speed; Blue wire for Med speed or Red wire for Slow speed. Counter clockwise rotation results in Hi speed yet clockwise (using Black Hi speed wire) seems to be no more than Slow speed. The capacitor connects with 2 brown wires, one having a white stripe and is rated 5.0 mdf 440/370 vac/b; it was purchased with the new/replacement motor. Unknowingly this motor ran for 4 or 5 months in the counter clockwise (wrong) direction. This was discovered while exploring the cause of the evaporator coil freezing-due to improper fan rotation. Thanks for your interest!!
Could be as simple as not moving air effectively when spinning the wrong way, so no load (or small load) on motor. Spin the right way, air is moved, motor slows down, work is done. Try blocking off the intake or output and see if the lack of air movement causes the fan (& motor) to speed up again.