I just took my truck,'99 F150 4x4 4.6L, into the dealership to have recall work done on it (speed deactivation switch). Now the AC will only come on when the blower is set to High. I took it back to them; they said they had nothing to do with it, but they would be happy to diagnose the problem for $150.00. They probably didn't have anything to do with it, but it looked pretty suspicious at the time. I digress.

Does anyone know what the problem could be? I check the fuse, it's fine. Any help would be great! Thanks!

 

They had nothing to do with it. Coincidence.

Probably the blower motor resistor pack. Pretty common failure and your symptom matches perfectely.

Steve

 

dittos

 

Thank you both, that fixed it! The whole unit that was in the air duct was rusted. Is this normal?

Anyway, Thanks for your help!