From your description the most probable causes are a clogged radiator and/or inoperative fan. Before replacing anything read these
troubleshooting tips to see if you've missed anything.
When checking coolant level dont check the bottle. Check by opening the radiator cap. It is on the right hand front side of the engine on the thermostat housing. Remember to only open this cap on a cold engine.
In order to test the fan motor connect battery voltage to pins 1 and 2 of the fan connector (That is the 2 pins closest to the v-shaped tabs on the connector)
On the 2.0 and 2.4l cylinder engines the waterpump is powered by the toothed side of the cambelt and it is therefore impossible to slip.
On 2.5l engines slippage may occur if there is oil leaking onto the cambelt. This can only be verified by removal of the cambelt covers.
Open the heater control to full hot and let the vehicle idle until operating temp is achieved. Let it cool down and check the coolant level again.
As for the A/C, you can remove the electrical connection on the A/C compressor in the engine bay and then use the A/C to operate the secondary fan.