Air-source heat pump outdoor unit beside a house in the snow
Generic photo: PeterEastern · CC BY-SA 4.0

Field pattern: heat pump 'smoking' or blowing cool in winter (normal defrost and aux heat before a fault)

All of these are normal parts of a defrost cycle: the unit reverses briefly to melt frost, the fan stops, melt water steams off the coil and backup heat may come on. The wrong turn is treating a normal defrost as a failure, or the opposite, dismissing a unit that is truly stuck in defrost or encased in ice. The job is to separate the two.

Cross-checked ~30 min easyBrands: All

Before you start

  • Do not chip ice off the outdoor coil with tools; fins and tubing are easily punctured
  • Steam that is dark, smells of burning or comes from the electrical compartment is not defrost: shut the unit off and investigate
  • Reversing valve, refrigerant and charge diagnosis are BLOCKED: refer to an EPA 608-certified technician

Diagnostic steps

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Field pattern: heat pump 'smoking' or blowing cool in winter (normal defrost and aux heat before a fault) · OnCall Tech