No, the outdoor condensing unit fan does not run during a standard heat pump defrost cycle. When the defrost control board initiates a defrost cycle to melt ice off the outdoor coil, it temporarily reverses the refrigeration cycle so the outdoor unit acts like a condenser instead of an evaporator, while simultaneously shutting off the outdoor fan motor. Turning off the outdoor fan is a critical step because it prevents cold outdoor air from blowing across the coils and chilling them, allowing the heat pulled from inside the home to melt the accumulated frost and ice rapidly. During this time, you may see steam rising from the outdoor unit. You can verify that the cycle is operating normally when the outdoor fan stops spinning and restarts automatically once defrosting concludes.
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