A modern heat pump does not perform defrosting using only a timer. It uses sensors and control logic to estimate if ice has formed.
External exchanger sensor
Measures the coil temperature and helps assess whether icing conditions exist.
Outdoor air sensor
Provides information about the actual environmental conditions.
Operating time
Many controllers also consider how long the compressor has been running continuously in heating mode.
Incorrect reading
A sensor with poor contact, incorrect positioning, or electrical deviation can cause excessively frequent or insufficient defrosting.
