The Technician scratched his head and surveyed the scene. He then asked himself, “It’s dead, but what is it supposed to do?”

Methodically, like a detective, he breaks down the purpose of a Motor Control Center (MCC), and how it relates to the downed HVAC unit. An MCC is a group of one or more encased sections with a common power bus, which contains motor control units. Every motor controller in an MCC can be programmed with a range of options such as separate control transformers, control switches, extra control terminal blocks, assorted types of thermal or solid-state overload protection relays, and various classes of power fuses or types of circuit breakers. For each cube you see in an MCC, that cube controls one motor.


Knowing two things: 1) the power is down on the HVAC unit and motor controller, its 28 degrees Fahrenheit outside, making the boss very unhappy about the situation and 2) it is his job to get it back up and running, our Technician then begins troubleshooting the list of problems that could be the cause. Is it the HVAC unit itself, Control Power Transformer, Fuses, a Contactor? Be sure to follow along as our Technician pursues the clues and solves the mystery in the coming weeks.

Learn how to troubleshoot like a detective, today, with TTS’ Troubleshooting Training!