A/C outside unit made brief shrill sound

My 24-year-old Carrier unit made a brief shrill sound while running recently. I had my wife turn off the unit at the thermostat before I had a chance to determine where exactly the sound was coming from. Later, we turned on the unit and it ran flawlessly as before without that earlier noise. I initially thought the bearings in the condenser motor were going bad and lacked proper lubrication thus the screeching sound. However, we have not been able to duplicate the noise a second time even though the unit has been running for several days now.
If the condenser motor is at fault and should make the noise again while I am away and unable to turn off the A/C, will any harm come to the rest of the components if the motor seizes up or just stops running? Will my compressor continue to run or will the unit sense a fault and automatically shut down?
I have located the exact replacement condenser fan motor and if I would be wise to replace it should I also replace the capacitor at the same time. The company that sell the condenser motor says it is not necessary to replace the capacitor. Wonder why he would say that since they are not all that expensive and with a unit nearly 25 years old it would seem prudent to replace it as well. Salesman also suggested that I touch the motor while running with a long slotted screwdriver and put the other end to my ear to listen for a bad motor. Any merit in this suggestion?
For peace of mind, should I just go ahead and replace the condenser motor and capacitor since my unit is so old? Or should I just wait to see if unit acts up again and then replace motor? I might add that this unit has served us seasonally quite well since its installation and has never had a service call in all those years.

 

Welcome to the forums.

If you put a new fan motor in a unit that old the compressor will get jealous.
Units were built to last back then. I just installed a contactor in my +20 year old Rheem compressor.

The new motor should have the required size of capacitor listed with it. It's not always the same as the original cap. I just mentioned my contactor as yours may be getting old too. Check it out for burned/pitted contacts.

 

You should definitely replace the capacitor if you replace the motor.

Does the motor spin freely with power removed?

I have not tried a screwdriver to my ear but it doesn't sound safe. A clamp on amp meter would be a better idea.

 

bearing might be dry from the winter snows...do you cover the condenser in the winter..does the shaft move up and down at all that sound might of been produced from there...a healthy spray of WD40 down the shaft into the top bearing... ....if the compressor craps then you go for a new condenser $$$