2004 Hyundai Sonata 2.7 DOHC I have replaced the water pump, radiator and cap, and thermostat. The temperature can maintain stop and go now but when you turn the air on and both fans kick on the temperature rises this also happens when I turn the heat on and both fans are running.

 

Prior to the over heating, was any work done on the vehicle?
Did you do a flush of the cooling system?
Are you sure you refilled the cooling system to full?
Sometimes air can get trapped inside the engine

When you turn on the AC, does the rpm go up?
It should go up in response to turning on AC.
Both fans are suppose to turn on when AC is turned on.

 

The only thing done was the Ac was charged. I have made sure there is enough coolant and have burped it. Yes the rpms go up when the ac or heat is turned on. I didn’t flush the system since I replaced all the parts to cooling system.

 

Maybe need flush?? Internals of engine not transferring heat to coolant.
Engine heats up when stressed (AC turned on)

 

There is a fairly good possibility of something else going on.

Sometimes when a circuit gives the incorrect info to the computer controlling things (Could involve Body control issue)
The system will resort to limp mode to prevent further damage. If all the usual mechanical steps don't produce a fix, we'll watch and see how it goes before jumping the gun.

Something I would suggest and that is to verify the engine temp is really as high as the indicators are saying. Gauges do provide incorrect readings based on info sent and the system reacts based on that info.