Which is it? If you have an automatic climate control system, it should be using a relay/transistor combo, but manual systems would have a resistor in place of the transistor and lack a high motor relay. Be specific, even though it sounds like you will get to the bottom of this before we do.

Keep in mind, regardless of which system you have, the failure of the motor itself tends to be inconsistent, see here. I was always able to get the motor to run if the current was high enough, but when the power was limited to 30A, it would come on sometimes and sometimes would stay off.