I have 2 white wires leading to my t- stat, how can I tell which one controls heat

If you only have two then it's both.
You can't have more than one function with only two wires.

Red and white I assume?

I have 2 white, 2 blue and 1 red. Don't know which controls heat or a/c.

Can I connect heat without fan

Then sorry, but I have no idea. That is an odd combination.
I'd have to see where they go and how they are terminated.

Red, white and blue go to furnace... and blue and white go a/c... is there a way to test which wires control heat