my coolent fan comes on when it wants to

That's how a coolant fan works- comes on when the engine coolant reaches a certain temperature- switches off when the fluid cools- are you saying that the gauge reads hot and your fan WON'T come on?

Just like jamnblues says, electric fans are designed to work that way. They will also cycle (come on and go off automatically) with the Air Conditioner.

Normally the fan comes on and stays on with the air conditioner. There is also a sensor on the engine, and if the coolant passes a certain temperature, the fan comes on until the coolant goes below a certain threshold. If the car is running hot without the fan coming on properly, check that sensor on the engine. It is often mounted on the intake manifold, but for sure it goes into the water jacket.

replace your ect (engine coolant temp) sensor and check wiring to it.