Understanding Inductor Operation and Troubleshooting

HVAC Inductor

The Faraday Law of Induction showed that if the magnetic field surrounding a coil changed, due to changes in current, then an electromotive force (EMF) of voltage & current is induced to the coil that opposes the primary current into the coil that created the magnetic field in the first place. As a result, inductors oppose any changes of current through them.

Most inductors used in the HVAC industry have Iron Cores, similar to a low voltage transformer, but only have two wire leads.

HVAC Inductor

Large motors which must use large VFD drives, will generate high voltage harmonics into the building power system and can cause extreme damage to other building electrical system components and also reduce the effective power delivered to the motor.

VFD’S employ a variety of inductors to impede, or choke down these high voltage harmonics which (Conditions the power). Severe building harmonics have caused elevators to shut down and clocks to lose time.

What is a "choke"?



An inductor placed in series with a conductor (wire), blocks, or impedes changes in current. Because inductors restrict, or choke changes in current, they are called “chokes”. Inductors are employed in electrical circuits to reduce EMI (electromagnetic interference), by attenuating high frequency noise in order to meet EMC (electromagnetic compatibility) emission and immunity requirements.

In this coil configuration, the inductor (reactor) blocks AC current, but allows DC current to pass.

Carrier and Bryant ductless condensers which may have inductors can be tested using an ohm meter, they should read very close to 0 ohms, if good.

Building power systems must have clean power for proper operation of all electrical devices. VFD’S have filtering components which must stop voltage harmonics from being generated into the building power system. The VFD’s have built in filtering circuits which usually includes “Inductors”.