Overheat A/C not on error

i left work yesterday and got on to the highway for about 5 miles an i looked at my temperature gauge and i was in the red and a messege says something like "overheated a/c not on." i put the car into neutrel and shut the key off and coasted on the side of the highway where i popped the hood and was expecting to smell some kind of hot burning smell or to hear the radiator bubbling but didnt.. so i started it up and drove home without it going over 3/4 hott.. and it continues to do so this morning and on the way home from work.. ANYBODY have any ideas?:confused: would be GREATLY appreciated

Check the following in the following order.

1. Check coolant level

2. Check that fans are turning on

3. Check coolant bypass line

4. Check headgaskets

Thanks i ended just going up to get a radiator flush and there was a pin hole in the coolant hardline going to/from the heater core and the waterpump..