Why is my van's gauge showing it's over heating when it doesn't smell hot?

I added a little antifreeze, wasn't really low. I haven't had any work done. I noticed that if I tried to use the a/c, it only ran on high...not medium or low speed. Could this have something to do with it? I drive it to the bank, and the gauge starts going up. Hope you can give me some direction.

is the radiator cooling fan coming on?and no the a/c switch not working on any seetings but high not problem.the blower motor resistor is the cause of motor running on 1 speed only.open hood and start engine let it run a few minutes and you should see cooling fan turn on.fan behind radiator,motor side.keep hands away from fan.