34 yes 34 at that point in decision box 614 outdoor fan loading is checked to determine whether fan motor load has increased to a point where airflow is substantially normal indicating that ice has melted more particularly in decision box 614 the then prevailing v f v l ratio is compared to a factor of 1 02 times the reference ratio r f0 stored in fig8 box 556 if the answer to the 34 less than 34 comparison of decision box 614 is 34 yes 34 then it is assumed that the evaporator is free of frost and the defrosting operation is terminated at box 616 if the answer in decision box 614 is 34 no 34 then the fan motor is de energized in box 618 and program execution returns to box 602 to begin another five minute defrosting interval before the fan is again momentarily started to check for frost blockage referring finally to fig1 depicted is another flow chart which may be employed in combination with the flow charts of fig7 and 8 to guard against the possibility that a defrosting operation is needed immediately upon compressor startup such could occur when a defrosting operation in progress was terminated prematurely by a momentary power interruption or by user action for purposes of fig1 it is assumed that the compressor motor reference ratio r c0 has been stored as indicated by box 528 in fig7 the compressor defrost algorithm of fig1 entered at 580 a compressor loading interval is established for example ten minutes by decision box.