[ModMech]

Generally Ford uses a grounding speed control system. Meaning that the blower motor has +12Vdc applied anytime the system is "on", and it varies the resistance in the ground circuit. The most common cause is a bad motor or motor resistor. To check the motor, apply 12V to one terminal, and ground the other. It should turn... FAST. If not, the motor is bad. Now, with ATC I'm not SURE if Ford still uses the standard resistor block, or if that is integrated into the ATC controls. In any event, with the connector unplugged from the motor, using a volt meter, check for the voltage to both terminals. You should have 12V on one, and ground on the other. Now, you have to measure the voltage between the two terminals as you select different fan speeds. Higher speed is higher voltage. I suspect that either the motor is bad, or you have no ground.