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HVAC School - For Techs, By Techs

Jul 9, 2024

In this short podcast episode, Bryan answers a listener-submitted question: How do inverter air conditioners work?

Inverter-driven systems have variable capacity to match loads. We can provide cooling or heating BTUs to match the needs of the space without overcompensating or undercompensating and causing temperature swings. Load matching also helps us get better efficiency out of the system. High-humidity climates also benefit from load matching, as equipment doesn't dehumidify well unless it has been running the entire time.

When set up and designed properly, variable frequency drives (VFDs) improve comfort, efficiency, and even dehumidification. You can "overclock" your compressor to get more BTUs out of it without oversizing, particularly when you have high heating loads due to the cold weather.

Inverter-driven equipment takes AC power in, runs it through a rectifier circuit, and turns it into rough power that resembles DC power. The current is then smoothed out and goes through the inverter bridge circuit. Unlike an analog AC wave, we rely on pulse-width modulation (PWM) to simulate three-phase power and control the motor speeds according to a space's needs.

We typically troubleshoot residential inverter-driven equipment by following the manufacturer flowcharts and possibly by communicating with tech support. Commercial VFDs are external to the motors and tend to be a bit more universal rather than manufacturer-specific.


Watch the livestream about VFDs & inverters with Matthew Taylor and Corey Cruz HERE, and you can also watch the livestream about cold climate heat pumps with Ross Trethewey and Russ King HERE.

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