[LazyPup]

As is true with nearly all AC motors, the A.O.Smith F48J66A48 is a PSC (permanent split capacitor) motor and it does not have an internal relay.

Although PSC motors do have two sets of windings, and one is commonly called the "run winding" while the other is commonly called the "start winding" in reality that is not correct.

When a motor has a true "start winding" the start winding is only energized momentarily during start in order to overcome inertia and establish the direction of rotation. Once rotation has begun and the motor spins up to its rated RPM either an internal governor relay or an external potential relay drops the start winding out of circuit.

In a PSC motor there are two identical sets of run windings, the inner winding which is called the "Run winding" and the outer winding, which is commonly called the "Start winding". When the power is first applied to the motor the inner winding is wired directly to the power source and is energized immediately. The power for the outer winding is then passed through a capacitor which causes a momentary time delay before energizing the outer winding. The time delay results in a slight differential between the theoretical center of the magnetic field in one winding in relation to the center of the magnetic field in the other winding. The differential between the magnetic fields establishes and maintains the direction of rotation thus in a PSC motor the "start winding" remains in circuit the full time the motor is running.

If a PSC motor will start when bumped as mentioned above that is a prime indicator that either the capacitor or the wiring for the start winding is defective. It should also be noted that if the motor is bumped and runs, it will overheat in a very short time.

The best method of testing a capacitor is to use a "capacitor tester" which has the ability to check the value of a capacitor under load, however as a rule capacitor testers are relatively expensive and seldom used in the real world outside of a shop.

A simple yet very reliable method of testing a capacitor is to use an analog VOM (volt,ohm.mili-amp meter).

You begin by disconnecting the main power source from the condensing unit then use a well insulated screwdriver to touch across the two poles of the capacitor to discharge any remaining charge it may be holding. (Do not take this step lightly, capacitors can store a tremendous charge. Absolutely never touch the contacts on a capacitor until you have discharged it, even if it has been out of circuit for months).

With the power off and the capacitor safely discharged you then remove the wires from the capacitor.

Now set your VOM to the highest resistance scale and hold one probe of the meter on one terminal of the capacitor while you touch the opposite terminal of the capacitor with the other probe. If the capacitor is good the needle on your meter will immediately swing up to about 1/3 to 1/2 scale, then begin falling back like a windshield wiper on your car. Reverse the probes and touch again, it should again repeat the upswing and drop off.

If the meter needle does not move the capacitor has a open circuit and needs to be replaced.

If the needle moves to full scale and stays there, the capacitor is shorted and also needs to be replaced.

When replacing capacitors on PSC motors we should make every effort to replace it with the exact value and when replacing a motor we must check the motor spec sheet to determine if the new motor uses the same value capacitor or if you will need a different one. (Personally, i make is a practice to always get a new capacitor matched to the new motor spec.) When it is necessary to replace a capacitor with a different value you must have a capacitance value equal to or greater than the original but you under no circumstances should you oversize more than 50% above the original rating for the motor.

The A.O.Smith motor, model number F48J66A48 listed above is a 1/4HP 208/230v 1Phase 850RPM PSC type motor and it is rated for a 5ufd capacitor.