I am rewiring a 1725 rpm, single phase 1/3 hp AC GE Industrial motor Model 5KH39QN9397C. It has four wires: red, black, yellow and green. Label on motor states that line voltage is red-black and green is ground but does not mention the yellow wire. Resistance between the wires is red-black = 4.8 ohms; yellow-black =3.1 ohms; yellow-red = 2.2 ohms. What is the role of the yellow wire? Will connecting the red and black to line voltage cause the motor to run @ 1725 rpm? Will connecting line voltage to red and yellow or black and yellow cause the motor to run at a different speed?
It is a split phase motor, but there is no capacitor in a split phase motor design. CSCR (Capacitor Start - Capacitor Run) or CSIR (Cap start-Induction Run), yes. But a Split Phase is used specifically BECAUSE it doesn't need a capacitor to make it turn the correct direction.
Here is the wiring diagram. You don't touch the yellow wire (or the blue for that matter). https://www.grainger.com/ec/pdf/6XH45_2.pdf
You can change the direction of the motor, you cannot change the speed.