Heat Pumps

Reversing valves, defrost, balance point, aux/emergency heat, charging in heat mode, dual fuel and low-ambient behavior.

5 guides

• Charging a Heat Pump in Heat Mode
  Why charging a heat pump in heat mode by gauges is unreliable, why weigh-in is the preferred winter method, and the conditions under which subcooling/superheat readings in heat mode can be used — plus the gotchas that make cold-weather charging tricky.
• Dual-Fuel (Hybrid) Heat Pump Systems
  How a dual-fuel system pairs a heat pump with a gas furnace, why the two heat sources must never run together, how the changeover (switchover) temperature is set using the economic balance point, and the control logic that makes the handoff happen.
• Heat Pump Balance Point and Aux/Emergency Heat
  What the balance point is and why it matters, how a heat pump's capacity falls as it gets colder while the building load rises, when auxiliary heat is supposed to engage, and how aux differs from emergency heat — plus outdoor thermostat lockouts for the gas-fired/strip backup.
• The Defrost Cycle and Defrost Board Basics
  Why a heat pump frosts its outdoor coil in heat mode, how the defrost cycle clears it, the difference between time/temperature and demand defrost boards, and how to read and test the defrost circuit in the field.
• The Reversing Valve: How It Works and How to Tell If It's Stuck or Bleeding
  How the four-way reversing valve switches a heat pump between heating and cooling, how the pilot solenoid actually drives it, when the coil energizes (O vs B), and how to diagnose a stuck or internally-bleeding valve in the field.

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