A light layer of frost or thin ice covering your outdoor heat pump condensing unit is entirely normal during cold winter weather, especially when ambient humidity is high and temperatures hover near freezing. To manage this normal frost accumulation, every modern heat pump is equipped with an automatic defrost control board that initiates a defrost cycle every thirty to ninety minutes, temporarily reversing the refrigeration cycle to melt the ice away. However, it is NOT normal for a heat pump to freeze up completely into a thick, solid block of persistent ice that does not melt during automatic defrost cycles. Severe, unyielding ice buildup indicates a mechanical or operational fault, such as a failed defrost sensor, a stuck reversing valve, restricted outdoor airflow, or a low refrigerant charge. You can verify normal operation when frost clears automatically within ten to fifteen minutes.
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