Rooftop Heat Pump Lockout Strategy (or lack of)

When you are pumping heat in, the inside coils are warmed and so the outside coils are being chilled. Running continuously in low temps the outside coils can freeze and ice up.

More sophisticated systems like the one we have at home monitor the outdoor coil temperature and will periodically defrost. The strikeout or timeout strategies are less sophisticated methods employed to keep your unit from turning into an ice block and self-destructing.