I want to replace a receptacle in a 220 line. When I opened the unused box I found a very strange collection of wires. There are two whites, one ground, two blacks ans 1 red. My belief is that there used to be a wall switch for the AC. I was trying to test for which are the hot with a multimeter but I must be doing it wrong. Please help.

We don't know how the receptacle was wired. However, for a straight 240, 220 doesn't exist anymore, I would use the red and black. If you get 120 VAC between red or black and ground, you should have 240 between red and black. The other black and white would possibly indicate a switch loop. You will need to start voltage checking to see what combinations you get.