In this LIVE episode, we talk about diagnosing inverter-driven systems. We also discuss some of the issues and solutions for over-voltage.

Inverter-driven systems, also called variable frequency drive equipment, provide comfort control across multiple zones in a building. Some systems may have multiple branch boxes that control various units throughout a building. These systems require a lot of patience; the diagnostic process can last a long time because you must test all of the terminals. Since these systems are very electrical-component-heavy, you may also encounter issues presented by lightning, power outages, or continuous high voltage. Installation errors are also common and can cause performance issues, such as incorrectly torqued-down terminals, nicked wires, and improper wire types.

When these systems are on, line voltage runs into a bridge rectifier. So, the equipment takes alternating current (AC) and turns it into a form of direct current (DC). Capacitors smooth out the sine waves before running that current into the inverter, which switches the power into three separate phases, but the power doesn't look like typical three-phase AC power.

Many power companies are familiar with single-phase AC equipment, so inverter-driven systems present a challenge. These challenges become clear in equipment near the initial power distribution source; inverter-driven equipment near the beginning of the power line is prone to excessive voltage and failure.

We also discuss:

• Power surges and electrical damage
• ICM493
• Loose connections
• Grounding
• Shielded conductor usage
• Pulse-width modulation (PWM)
• 230v-rated equipment
• Multi-stage equipment and airflow
• Bernoulli's principle
• Carrier Infinity equipment and locking out stages
• Ductwork and diffuser sizing
• Controlling radiant heat loads with multi-stage equipment
• Ventilation vs. dehumidification vs. heating and cooling
• R-22 retrofit refrigerants
• Metal oxide varistors (MOVs)

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