A bad condenser fan motor is a common problem with HVAC units, all year long they are exposed to the elements and are required to turn on and off constantly blowing the air away from the condenser. Often they will freeze up after the bearings seize or they will draw the wrong amperage and stop working.
A condenser fan motor is responsible for pulling air out of a unit pulling it out past the condenser, much like a fan and radiator in a car or truck. During the summer when it is hot it will blow the heat away from the condenser through its fins cooling down the refrigerant that flows inside.
When a condenser fan motor goes bad often the HVAC unit will work initially then stop. For example during the summer when it is hot and a unit is turned on it will at first blow cold air then after a short period it will stop and blow room temperature air.
A simple way to tell if a unit has a bad condensing fan motor is to turn the unit on and stand next to the condenser. The fan at some point should kick on and blow out air. The fan does not run constantly only when needed but if twenty minutes or more go by and the fan does not kick on then there is most likely a problem.
When a fan motor is not spinning a small stick can be used to reach the blades and give them a nudge which sometimes will get it running again but will soon stop. If the motor will not spin at all then the bearings are most likely are bad and the motor will need to be replaced.
Be careful when working with a fan motor the blades turn at a high RPM and can cause injury. Never put arms, fingers or any body part in the path of the blades. Also before removing a condensing fan motor be sure the power to the HVAC unit is off. A bad motor can suddenly start working again and if not bolted in place will spin out of control causing damage. The same thing can happen if a new motor is installed, or problem fixed and the power is on.
Always be aware that the fan may be good and the problem may be something else such as bad connections, blown fuses, contactor, or bad start run capacitor. Each of these will need to be checked to be sure the fan motor is bad. Multiple failures can happen in a unit at the same time especially as a unit ages.
Main components to check
Fuses/Power: Checking the fuses or breaker should be the first thing to look at. If the unit has a Disconnect be sure it is inserted properly. Opening up the side panel and checking the voltage is often the quickest way to be sure the unit is getting power. The majority of units use 240 volts this can be verified by looking at the name plate on the HVAC unit.
Contactor: A Contactor can become pitted and dirty with use and can build up a resistance or become open. When this happens a fan motor will not be able to turn on. The resistance can be checked with a meter from one side to the other if the resistance is high then it should be replaced as a Contactor should have very low resistance.
Start Run Capacitor: The Start Run Capacitor is often combined into one capacitor called a Dual Run Capacitor with three leads, but can be split between two separate capacitors. The Start Capacitor gives a fan motor the torque it needs to start spinning then stops; while the run capacitor stays on giving the motor extra torque when needed.
If the Start Capacitor fails the motor will most likely not turn on. If a Run capacitor goes bad then a motor can turn on but the running amperage will be higher then normal causing the motor to run hot and have a short life expectancy.
After replacing a bad condensing Fan Motor a new Start Run Capacitor should always be installed.
A Dual Run Capacitor has three connections HERM, FAN and COM.
HERM, connects to the Hermetically Sealed Compressor
FAN, connects to the Condenser Fan Motor
COM, connects to the Contactor and provides power to the Capacitor.
If the unit has two capacitors then one is the Run Capacitor and the other is the Start Capacitor. One will be for HERM (compressor) and one for the FAN (fan motor) connection.
Hint: It is a good idea to take pictures, or write down and note wiring connections and wiring colors for future reference before starting.
Buying a new motor
Here is a label from a condensing fan motor.
If the exact model number can be found then that would be all that is needed besides verifying the numbers before installation.
But often the model number is unavailable, or it is cheaper to use a universal motor as a replacement. The easiest way to do this is take the motor to a local HVAC supplier and have them cross reference it, and match it to the bad motor. Be sure to also buy a new capacitor with the correct MFD and voltage.
1….. The operating voltage
A condensing fan motor is either single phase (1 PH) or three phase (3 PH). The voltage for residential is usually 240 volts but be sure to check. The voltages on the motor can sometimes be misleading such as the following.
120 volts can also be referred to as 110V or 115V
208 volts can also be referred to as 200V
230 volts can also be referred to as 220V or 240V
460 volts can also be referred to as 440V or 480V
2…..The Horse Power (HP)
3…..The shaft size, The fan blade needs to be mounted on the shaft at the same depth as it originally was set at. Basically the fan is pushed onto the shaft until it reaches the same location as it was before pulled. Be sure to check how far the fan blade sits inside the unit before pulling motor.
4…..The RPM (Rotation Per Minute)
5…..Mounting style, usually the motor is fastened to a curricular grate that bolt to.
6…..Frame, most HVAC motors are 48 frame, with a body diameter of approximately 5-5/8″.
7…..What direction the motor turns CCW or CW (counter clockwise or clock wise.) Most universal style motors have an option to reverse the direction of rotation.
8….. Number of speeds. Motors will often have multiple speeds. Different speeds may be necessary to adjust airflow for the specific installation, or for different operating modes.
Buying a new HVAC Capacitor
A new Fan Capacitor should always be installed with a new motor. A capacitor can be bought at a HVAC supply company there a usually at least a few even in a small town, also online eBay is a good place to look.
Here is two common capacitors, the one on the left is a Dual Run Round Capacitor while the one on the right is Run Oval capacitor.
The Dual Run Capacitor is nothing more than two capacitors in the same housing; while the Run oval is a single capacitor and a HVAC system will usually have two.
Capacitors are measured by the Microfarad sometimes shown by the letters uf and Voltage. In any HVAC unit the capacitor must match the motor.
The voltage can go higher if necessary but never lower while the MFD (uf) should always be the same. In the picture this is a Dual Run Capacitor and reads 55+5 MFD (uf) 440 VAC. The larger number 55 MFD is for the compressor while the lower number 5 MFD (uf) is for the fan motor. The lower number is always going to be for the fan motor. Then the voltage 440 Volts AC.
(The + -5 after the MFD is how much it the capacitor tolerance is rated to go up or down.)
To order a replacement for this capacitor it would be 55+5 MFD (uf) and 440 volts AC Dual Run Capcitor.
Testing a HVAC Capacitor
Testing a HVAC capacitor is done with a HVAC multi meter, the multi meter must be cable of reading the range that a HVAC capacitor can have. Many small electronic meters do not have this range. Here I am using the Fieldpeice HS36 multi meter with an Amp clamp
This test is being done on a Dual Run Capacitor 55+5 MFD (uf). The multi meter is on Farads and the leads are on C and FAN (positive and negative do not matter). The lower number is for the fan motor which is rated at 5 MFD (uf), and it reads 5.3 MFD (uf) so it is good. The leads C to Herm can be read also which would be for the compressor.
Here is a single Run Oval Capacitor rated at 5 MFD (uf) and 370 volts AC
To test a Run Oval Capacitor simply touch the two leads. This one reads 4.5 MFD (uf) and is rated at 5 MFD (uf), so it is bad and needs replaced.
Replacing the Start Run Capacitor
A new fan capacitor should always be installed when a new motor is installed. It is always a good idea to take a picture or write down wire coloring and connections.
1…..Turn off the power to the HVAC unit and verify it is off with a meter.
2…..Find the side panel were the electric is fed into the unit and remove the panel.
3…..Locate the Stat Run Capacitor, if it is a Dual Run capacitor there will be only one. If there is two then only the fan motor capacitor will need to be replaced.
4….Verify the MFD and voltages, then connect the new connections from the old capacitor to the new capacitor one leg at a time to be sure the conations are correct.
(If you have two capacitors then one is for the compressor and one is for the fan motor.)
Replacing The Condenser Fan Motor
Be sure the power is off on the HVAC unit by turning off the breaker, or pulling the disconnect. Do not turn the power back on until the motor is back in its place and bolted in.
It is a good idea to take pictures of the wiring connections and motor to refer back to if necessary.
1…..Turn the power off to the HVAC unit and verify it is off with a meter.
2…..The fan motor will be under a circular grill and be bolted to the HVAC unit unscrew each of these bolts or nuts and set them to the side.
3…..Note how deep the motor sits in the HVAC unit as the new motor should sit in roughly the same spot. Pull the motor and the grill out of the HVAC unit. The wiring can be cut with wire cutters if the wiring is in place to tight.
4…..Note which way the fan blades sit then remove the fan motor from its shaft. The fan blades must turn correctly, and should be placed to pull air out of the unit, if they are placed in the wrong direction the unit will not work correctly.
(Often the end of the shaft is rusted up from the elements making the fan hard to remove from the shaft. Use sand paper to remove the rust from the shaft making it easier to pull off.)
5…..Place the fan on the new motor being sure the blades are in the correct position.
6…..The wiring will now need to be connected, be sure to keep the wires tied up away from the blade. There should be a schematic on the side of the new motor showing which color wire goes were. A schematic should also be some were around the access panel.
(There will be a lot of air pushing the wiring around so be sure to wire tie the wires into place. The wires should never be able to touch the blades.)
If it is a three wire motor then one connection will go to the FAN on the new Start Run Capacitor. The other two wires are for power and will go to the contactor for 120 volts on each leg for a total of 240 volts.
If it is a four wire motor then look at the schematic on the side of the motor for wire color. Two wires are for power and go to the contactor the other two wires will go to the capacitor.
(If you order a new motor, and there is four wires while the original had three wires then two wires are for power and the other two wire need to be run to a capacitor. If the original capacitor is a Dual Run Capacitor with only one leg for the FAN connection buy another capacitor to only run the fan motor. Look at the motor for the MFD and Volts. It will only need to be a single capacitor with two connections. Following the schematic on the side of the motor two wires will go to the power and the other two wires will go to the capacitor.)
Note: Sliding the wiring through to the connection points can be a pain at times. If you are very careful to check the coloring of the wires then they can be cut and wire nuts can be used to connect to the old wires. Although this is not recommended it can be done in extreme cases were the wires are all but impossible to get through the unit.
Testing the Amperage
A amperage test should be done to be sure everything has been done correctly. Here is a HS36 multi meter with an Amp clamp showing the amperage from the fan motor. This Fan motor was rated at 1.6 amps, anything under that would be good. Here it is showing 0.8 amps well below the 1.6 amp rating.
If this is not an option then close up the unit and power it on. Neither the fan motor or the capacitor should get to hot. There is a temperature rating on the name plate of each motor if it goes above this it can shut off and possibly damage the motor.
All information written here is for HVAC students, technicians or properly trained personal. Do not attempt any of these procedures without the proper training. Replacing a condenser fan motor can be dangerous do not attempt this without proper electrical training, construction training and safety practices.