Condenser fan problem

To whom it may concern,
I have a 2006 pontiac gran prix and lately is being using too much coolant. I found out that the condenser fan was not coming on at all even when the temp was a little more than half way and the vehicle has been idling. The only thing that makes the fan consenser motor turn on is by running the fan control on my ac pannel. What could be wrong with my car. Any feed back on how I can correct this is appreciated. Than you for your time.