Air conditioner motors are some of the crucial components that are required in the operation of the air conditioning in your house. We will discuss the various types of single-phase motors that are used in your equipment at home. Here are four types of electric motors that are commonly being used. This is the simplest design where the RUN winding and START winding are connected in parallel and 90° electrically apart. It is usually used in small pumps, fans and blowers where the capacity is below 1 horsepower. It has a low starting torque but high starting current. Since the torque is low, the ability to start the motor is only practical for low load condition.The RUN winding is make from bigger diameter wire and shorter turn for lower resistance and high inductance properties. The START winding is make from smaller diameter wire for higher resistance and low inductance properties. When power is connected to the motor, both the windings will be energized with the current in the RUN winding lags the current in the START winding by about 30° electrically.

This out-of-phase effect on the stator produces a starting torque and causes the rotor to start rotating. Typically the speed of the motor is 1800 rpm or 3600 rpm when running without any load. When the load is connected, the speed can go down to 1725 rpm and 3450 rpm respectively.The no-load speed of the motor is given by:Speed(rpm) = (Frequency of AC power X 120)/number of polesFor example, if your supply is 60 Hz and the motor is using two-pole, the synchronous speed = (60X120)/2                             = 3600 rpmThere is a switch known as centrifugal switch which is connected in series with the START winding. prices on new ac unitsThis mechanical switch will open when the motor speed reaches 75% of the rated speed typically within 2 seconds. how to work on ac unitsOnce the switch opened, the START winding in circuit is disconnected. small ac units for sale

This is to protect the START winding from overheating. When the motor is powered off, the switch will close the circuit to get ready for the next starting of the motor.These days, electronic relay is also being widely used to disconnect the START winding.This motor is similar to the split-phase motor except that there is an external capacitor that is connected in series with the START winding. This capacitor will cause the current in the START winding to lead the voltage. The current in the RUN winding lags the voltage. When this happens, the phase difference between the two windings is 90° electrically hence a true two-phase starting is achieved. The starting torque of this motor is very high making it suitable to drive small compressor which needs to start under full load. The capacity of this motor can go up to 1 horsepower. Once the motor has reached 75% of the rated speed, the capacitor and the START winding will be automatically disconnected from the circuit by using the centrifugal swith, potential or current relay. 

After the capacitor and START winding have been removed from the circuit, the magnetic field being generated continuously will cause the motor to continue running. This type of motor is also known as CSIR motor or Capacitor-Start-Induction-Run motor.This motor design is similar to the capacitor-start design except that there is a second capacitor known as the RUN capacitor which is connected in parallel with the START capacitor and the switch. These capacitors are effectively connected in series with the START winding. During the starting of the motor, both the capacitors are connected in the circuit. The START winding and the RUN winding will remain connected to the circuit at all times. Usually the capacitance of the RUN capacitor is lower than the START capacitor. During starting, the effective capacitance is the combination of both capacitors causing a greater phase angle shift between the windings. This provides a higher starting torque and can be used to drive the compressor as well as in belt-driven motors.

As the rotor speed reaches 75% of the rated speed, the switch will be automatically open to disconnect the START capacitor from the circuit. The START winding remains in the circuit. The RUN capacitor helps to correct the power factor of the circuit making it more efficient. The capacity of this type of motor can go up to 10 horsepower and is one of the most efficient motors used in the HVAC industry.Permanent Split Capacitor(PSC) Air Conditioner MotorThis motor has similar design to the phase-split motor except that there is a RUN capacitor connected to the START and RUN windings. This motor does not have any switch and the START winding, RUN winding and the RUN capacitor are active whenever the motor is ON. This type of motor has low starting torque and is suitable to be used in small fan motors such as the fan coil unit of a split air conditioning system. Multi-speed PSC is achieved by changing the winding resistance. If high speed is required, the terminal is connected to the least winding resistance.

If low speed is required, the terminal is connected to the highest winding resistance. By utilizing relays to choose the terminal to be connected to the line voltage, different speed of fan motor can be achieved.In the diagram above, there are 4 motor speed that can be selected. Super High(SH), High(H), Medium(M) and Low(L). The selection can be done by using electronic relays to connect L2 to one of the four terminals depending on the speed required.See the different types of air conditioner blower or fan that are used in the HVAC equipment.In HVAC, motors are used in fans, compressors and pumps. Get a better understanding of the parameter of the motor and mounting styles.Read the different types of capacitors used in a air conditioner circuit. Back To Air Conditioner Motors Home PageFan motors are the unsung “heart” of HVAC equipment. They work unobtrusively and quietly for years, often under tough conditions. They don’t need a lot of love, but they do need periodic attention and it’s up to you to provide it.

The cost of overlooking regular testing and maintenance of motors can be an HVAC system that grinds to a halt, so be sure to check the motor on every maintenance and service call. When you arrive on a jobsite in which a unit’s fan motor is not working or the high-limit switch has tripped, the first thing to check is power to the motor and/or unit. If there is proper voltage, check the low-voltage control circuit. Check for proper voltage at the transformer and check for a fuse in the low-voltage circuit. Make sure the circuit breaker is not tripped (or the fuse is not blown). If the circuit breaker is tripped (or fuse is blown) or if the transformer is bad, it could indicate a short in the motor. In that case, check the windings in the motor before turning the power back on. To check the windings of a motor for an open or a short, you’ll need to measure the ohms. If the unit has a 120V motor, it will most likely have three or four colored wires (black, red, yellow, and blue are common), a white wire, and two brown wires.

Do a resistance check between the white wire and each of the colored wires. The higher the resistance, the lower the speed, with each color representing a different speed: i.e., four colored wires, 4-speed; three colored wires, 3-speed. You want to see a resistance reading. If you get a zero reading that means the motor winding is shorted and may be the cause of the tripped breaker/blown fuse. If you get an infinite reading (overlimit or OL on most digital meters), that indicates an open motor winding. If either of these conditions exist you will have to replace the motor. When checking the ohms on motor windings, many technicians have difficulty determining an open winding vs. a shorted winding. But it’s really not hard to tell the difference between the two. It should show a resistance. If it shows a zero reading it probably means the windings are shorted out. If it shows an infinite reading, that means the windings are likely broken or open. A good trick to remember this is that an infinite reading means the greatest resistance in the world.

It’s like an open door leading to infinity — in other words, an open winding. Meanwhile, a zero reading means the load is taking a short cut around it — in other words, a short. That’s just a simple trick to help you remember that a zero reading means a short, and an infinite reading means an open or broken winding. Just because a motor is not running doesn’t mean the motor is bad. If the power is correct and the motor is neither shorted nor open, check the capacitor (that’s where the two brown wires go). A capacitor helps the motor run and gives it more torque. If a motor doesn’t have the torque to turn the blower wheel or the fan belt, it won’t start. So the capacitor plays a big role. The capacitors on most of residential blower motors are very small, so technicians tend to overlook them. You should discharge the capacitor before handling it. Using a capacitor tester, make sure the microfarad reading is within 10% of the rated capacitance on the capacitor. It will be a number listed in uF or mfd, depending on the manufacturer.

If the reading does not match the rating, replace the capacitor. Checking 240V motors is slightly different because you will have two hot wires and most will be only single-speed. But you still ohm-out the windings to check for open and shorted windings and check the capacitor the same way. Finally, when doing a routine maintenance call on a unit, always check and clean the motor. One of the biggest problems with motor burnouts is dirt. The main thing to tell homeowners is to keep everything clean. Most of the furnaces in heating climates are located in a laundry room or a basement. In those rooms, lint and dirt kicking up from inside the house can block the motor holes and make a motor overheat. When motors overheat they burn up their windings and bearings. So a lot of bad things can be caused by dirt. Remind customers that not getting their furnace cleaned annually could void the warranty.    Phil Rizzo is an HVAC instructor at Coyne College, Chicago, IL. He can be reached by email at prizzo@coynecollege.edu.