Why it matters to you
Greater Houston has few freezing nights, but damp winter mornings near freezing are exactly when outdoor coils frost, so many homeowners first notice defrost as a cloud of steam or a short stretch of cooler air from the vents. That is normal; an outdoor unit that stays encased in ice is not.
Practical guidance
Let a defrost cycle finish on its own — it usually lasts only a few minutes. If the outdoor unit stays iced over or seems to defrost constantly, switch the system off at the thermostat and call a licensed technician; never chip or pour hot water on ice on the coil.