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HVAC School - For Techs, By Techs

Aug 17, 2023

Joey Henderson returns to the podcast to talk about heat pumps and inverters.

The reversing valve, defrost cycles, and auxiliary heat can cause confusion for people who have primarily worked with furnaces or straight-cool A/C systems. Heat pumps use defrost cycles and bring on the auxiliary heat when the coil is ice-bound, which can present a challenge; we need to maintain cold coils without going into defrost all the time. 

Even though heat pumps were significantly less effective in years past, we will still see reduced performance in very cold conditions with the newer inverter-driven systems. Proper design, installation, and commissioning will also help occupants get the best performance out of their heat pumps.

Inverters offer plenty of advantages for the cooling aspect of heat pumps, too, especially when it comes to achieving longer runtimes for dehumidification. They can also float their coil temperature, much like how refrigeration systems can use floating suction or head pressure. Condensate assemblies absolutely must be run properly to prevent backed-up drains and other related problems. Liquid line sizing and proper commissioning are also especially crucial for ductless inverter-driven systems.

Joey and Bryan also discuss:

  • Heat pump training and the electrification initiative
  • Balance point
  • Defrost strategies and universal defrost boards
  • Dual-fuel systems
  • Heat pump stigmas
  • Blower door testing in various climate zones
  • Surge protection and voltage monitoring
  • How inverters work
  • Occupant lifestyles and latent loads
  • Zoning and duct design for inverter-driven systems
  • Critical charge
  • Line length for ductless systems


Check out Joey's training, social media, and contact information at You can also check out Craig Migliaccio's book about mini-splits at

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