The easiest and most common way to check a unit is to quickly touch the top of it and while it should be warm it should not be very hot (too hot to touch) if so then there is likely a problem.
You can also measure the temperature with a thermometer, HVAC technicians often use infrared temperature guns that can read the temperature without ever touching the condensing fan motor but a standard thermometer will also work.
Every condensing fan motor has a temperature it can safely operate at. This operating temperature is written on the side of the motor name tag which also has all the information about the motor.
Most motors run around 70 degrees Celsius or 150 degrees Fahrenheit.
Sometimes the name tag can be easily seen and sometimes it will have to be lifted out to see. Lifting out a motor is easy as they are usually mounted to a circular grate that has 6-10 screws holding it in place.
Be sure the unit is off when removing any screws. HVAC technicians pull the disconnect or turn power off at the breaker to the unit before doing any work. No one wants a unit to kick on spinning the blades while they are working on it.
After checking the temperature it should be within the specified temperature range of the motor. If it is not then more than likely the motor is bad or something is causing it to over amp. Usual causes of an over-amping condensing fan motor is when it has the wrong start run capacitor or wrong fan blade. If no work has been done to it lately most likely the motor has gone bad.
Replacing a condensing fan motor is fairly simple and can save you a lot of money for the DIY (Do it yourself) type of person. An HVAC company will charge around 400 to 500 dollars maybe more to come out and fix it for you. While buying a new motor yourself runs 60 to 150 dollars.
Of course, care has to be taking, if a motor or start run capacitor is wired wrong then it can burn up a motor and cost more money. If you have wired up a wall socket, roof fan, or other electrical house hold items more then likely it will not be a difficult job.
There are many YouTube videos and books that can show the necessary steps.
Replacing the start run capacitor should also be done at the same time. Using the old start run capacitor with a new motor can damage a new motor.
The information needed for buying a new motor and capacitor are written on the side of each.
The problem for many DIYers is that places like Home Depot or any home supply store do not carry these parts. Finding an HVAC service company that will sell you the parts is an option but they usually mark up the prices when they sell to a homeowner. The good news is that these parts can be easily ordered online at Amazon or eBay.
Example Condensing Fan Motor On Amazon.
Fasco D7909 5.6-Inch Condenser Fan Motor, 1/4 HP, 208-230 Volts, 1075 RPM, 1 Speed, 1.8 Amps, Totally Enclosed, Reversible Rotation, Ball Bearing
The same can be done with the start run capacitor by looking at the tag for the MFD and voltage.
Example Start Run Capacitor On Amazon.
GE Genteq Capacitor Dual Run Round 35/5 uf MFD 370 Volt VAC 97F9834 (replace old GE Z97F9834) 35 + 5 MFD at 370 volts
For all the home Do-it-yourself people out there I’m sure replacing a condensing fan motor and start run capacitor will be a great way to save money.
Of course, if in doubt be sure to call a professional.