A heat pump in cold weather can collect frost on its outdoor coil. Many systems respond by briefly reversing to clear the coil, which is called a defrost cycle. That is normal behavior. What matters for planning is the pattern: how often the cycle runs, how long it lasts, and whether the frost clears completely. A pattern that drifts over the seasons is worth recording before anyone decides what it means.
What to watch on the walk-through
On each visit, take a few minutes at the outdoor unit. Look at the coil and the cabinet from the outside. Do not open the cabinet panels.
Note whether frost sits on the coil when you arrive, and whether it is clear when you leave.
Note any change in sound during a defrost. A new knock, grind, or rattle is worth recording in plain words.
Note whether the indoor supply air feels cooler for a short time during a defrost. Many systems do this briefly. A longer cool spell is worth recording.
Note any snow, leaves, or stored items piled close to the cabinet. Clear the space around the unit as the installer's manual describes.
Keep the log
Write each entry with its date, the outdoor temperature range you remember, the state of the coil at arrival and departure, and a line on sound and indoor feel. Plain sentences are enough. The log is useful because it shows a trend across weeks and seasons, which a single glance cannot.
Sort the causes before you call
A changed pattern can come from several sources. Some are yours to check: debris or snow around the cabinet, a thermostat setting that has changed, an indoor filter that has clogged the airflow, or a coil that has collected dirt. Some belong to a technician: refrigerant charge, sensors, the reversing valve, and any wiring. When you call, bring the log. Ask the technician to read the defrost settings, check the coil condition, and tell you which of the observed changes the visit confirmed and which it ruled out.
Pair the log with your fall furnace walk-through so the cold-season notes sit in one place, and compare the unit's age with the heat pump page. A pattern change does not by itself say where the unit sits in its span. It means the record now has something new to show.