How to Match an HVAC Motor (In-Depth Guide) | Spec. Sense

i unban sand welcome to speck cents fractional horsepower motors are a versatile workhorse used in appliances furnaces commercial HVAC equipment and pumps when sized correctly most motors can last for decades but overheating moisture and mechanical stress might cause a motor to fail earlier the motor nameplate is the key for finding a replacement as it lists the model number and electrical specs of the motor in some cases the model number can be used to find an OEM motor or a direct cross-reference if needed you can still use the motor specifications to find a proper replacement first match the physical specs this includes the motor diameter shaft size and mounting type then match the electrical specs which includes horsepower voltage amps rpm rotation motor type and capacitor size mismatching will reduce motor life and performance so it's important to find the right replacement an overloaded motor draws more amps runs hot and will be slower an under loaded motor will also overheat and be highly inefficient in this episode we'll take a closer look at each of these specs first measure the diameter and length of the motor next note the shaft diameter and length smaller motors will generally have a/c frame a 3.3 inch frame or a 4.4 inch frame motor is larger than five inches in diameter will use the standard frame sizes 42 48 and 56 now check the mounting type this could be a rigid base belly band or stud mount Drive motors we use a rigid base on the other hand direct drive motors will likely use a belly band now that you've narrowed down a motor of the same physical size it's time to match the electrical specs the motor horsepower refers to how much work the motor can produce at is rated voltage and speed for example furnace blower motors are generally one-eighth horsepower or more small utility fans are around one fifteenth horsepower or less next note the voltage rating this is the optimal performing voltage of the motor with a ten percent tolerance for fluctuations dual voltage motors such as those rated for both 115 and 230 volts can be wired and operated at either voltage the current rating or full load amps describes the current draw when the motor is operating at its full load the current will be different based on the horsepower motor type and overall efficiency keep in mind that not all motors of the same horsepower will function the same so it's still best to try to match both the horsepower and amperage next look at the motor speed and the number of speeds synchronous motor speed is the speed of the rotating magnetic field and is determined by the number of poles the rated motor speed will be lower than the synchronous speed for example a four pole 1800 rpm motor will likely have a rated speed of around 1700 and a six pole 1200 rpm motor will be around 1100 this is because all induction motors slip a little went under full load slip is basically a magnetic field offset between the windings and rotor that causes the motor shaft to rotate and generate torque torque increases as slip increases decrease the speed some motors will use several wire taps each with more resistance which increases the amount of slip these are multi speed motors and will often have multiple speeds and amp ratings listed if there is only one speed and one amp rating listed then it will be for the highest speed the direction of rotation is usually written as a code whether the motor rotates clockwise or counterclockwise define from either the shaft end or from the lead end now these are opposites so clockwise lead end is equivalent to counterclockwise shaft end keep in mind some motors are reversible and we'll have a diagram on the nameplate showing how to wire for each direction PSC and shaded pole motors are the most common motor type used in HVAC applications a PSC motor can be used to replace a shaded pole motor but not the other way around for the same horsepower rpm and speed shaded pole motors will draw twice the amps since they are half is efficient as a PSC motor therefore using a shaded pole motor to replace a PSC motor it's not recommended these motors will draw more amps and might cause the breaker to trip when replacing a defective motor it's also recommended to replace the capacitor capacitors are an energy storage device that provide the proper magnetic phase angle and torque needed for rotation this will either be a start capacitor in a capacitor start motor or a run capacitor in a PFC motor the capacitance expressed in micro farad's is a rating of how much energy that can be stored in the capacitor this should be matched exactly the voltage rating refers to the maximum voltage that the capacitor can be exposed to you can use a capacitor with an equal or higher voltage rating but never with a lower rating as this can result in capacitor failure dual run capacitors are used to support two electric motors like in air conditioners that use both a compressor and blower fan they will have 2 micro farad ratings the higher rating is usually for the compressor and the lower rating is for the fan another important factor is to consider the enclosure type this is determined by the motor application most HVAC motors will be air over motors and will use the air it moves to cool the motor as it runs a lot of these motors are rated for continuous duty larger motors are designed to be cooled by more airflow so putting a large motor in a low airflow system will cause heating issues air / motors come in two variations open air / motors have a vented housing and are used in clean dry areas like in furnace blowers totally enclosed air / motors are used in outdoor or harsh environments like in air conditioned air condensers open drip proof motors have vents in the bottom of the housing for passive cooling and will offer some protection from dripping water totally enclosed non-ventilated motors are used in dusty areas and are cooled passively hopefully this video has given you a better understanding of motors and how to find a replacement if you liked this and want to see more tutorials and informational videos then subscribe to our Channel and if you need help you can call or visit a name relocation to talk with our knowledgeable staff thanks for watching you

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