Atwood 8940-III fan won't stop

I should have stated to check the voltage at the red motor wire when the fan goes to slow speed. The fan should ALWAYS have the 12.9 or higher voltage at the fan if it is running. If it does NOT(lower than the voltage of the RV), then the control module is the highly probable problem as the motor gets its voltage direct from the Fan relay on that board. There are 2 red wires connected on 2 spade terminals of that board. One is the supply 12 volts for the motor and the other is the direct wire to the motor after the fan relay closes. BOTH of those wires should have 12.9 or higher volts when your malfunction happens. IF they BOTH have lower than line voltage, then the control board is not the problem. If one has line voltage(supply) and the other has a lower voltage then the board is indeed defective. You CANNOT test for this problem with a Circuit board tester as the problem appears to be HEAT related, since the furnace runs normally until it tries to cycle off. Doug