Arkansas HVACR NewsMagazine January 2021

S tate, National, Chapter News Tech News

Always make sure that blowers and compressors are running the right direction before leaving them running.

Internal vs. External Overload

Many motors have internal overloads that will shut the motor off when it overheats. Others will require an external overload either at the motor or more commonly built into the “starter” which is essentially a contactor and an overload relay combined.

Motor Rotation

3 Phase Voltage & Current Imbalance

A three-phase motor can easily run the opposite or possibly the wrong direction by swapping any two phases entering the motor. This means that blower motors and scroll compressors can easily run the wrong direction if they are wired incorrectly. Also, keep in mind that if the blower is connected to a VFD and the compressor is not the blower could be running in the correct direction because the VFD can correct the phase rotation.

Voltage imbalance is a motor killer. It causes poor motor performance and increased winding heat which leads to premature failure. In the case of HVAC blowers and compressors, this additional heat ends up in either the refrigerant or the air which must then be removed, further decreasing efficiency. To test for three-phase imbalance always check from phase to phase not from phase to ground with the motor running. You simply check the voltage