Several transmission embodiments selectively communicate rotary drive to an orbiting scroll to achieve capacity modulation. In these embodiments, when the motor is driven in a first direction, the orbiting scroll is driven at a rate which is equal to the motor speed. However, if the motor is driven in a reverse direction, the orbit rate of the orbiting scroll is reduced. The transmission ensures that the orbiting scroll member itself is driven in the proper forward direction regardless of whether the motor is being driven in forward or reverse.