I have a 2006 Nissan Altima. The A/C fan won't come on at all. What may be wrong?

The blower motor might have short brushes and needs replacement. The speed regulating resistor might be blown and need replacement. The fuse for the blower motor might be blown.

did you mean the ac motor or the compressor, if it is the compressor, it could be that you are low on refrigerant.

I tried to fill my 2006 Altima with refrigerant but the compressor fan never came on so it didn't take the stuff in. Now what do I do?

your ac gas in the system is too low you will have to jump the ac relay terminal #3 #5 to start the compressor its a blue relay under your hood on the passenger side.