The HVAC guy will install the AC but I need to get 220 v to the compressor. The house was wired when it was built and I have a 10/2 wire running from the panel to a box in the furnace room. The black is loose in the panel and the white is attached to a common.

The panel has one open spot but I will have to do a little doubling up to get the two I need for 220.

Here's the question: I think I need a red black white 10/3 to run 220. But the wire is 10/2. Can I get 220 to the AC unit? How?

You may be able to get a TWIN breaker for your panel. This gives two independent breakers in a single space, so you don't have to pigtail circuits.

The AC only needs 10/2. Neutral is normally not needed.

Sweet. I feel better. I am not totally capable of doing this but my expert friends are. I will get the right breaker somehow.

I assume we will run the white and black with power and take the white off the common?

Yep.

The TWIN breaker will replace two 120 V circuits.
The 240 V, 2 pole breaker (Handles move together) will be for the AC.

It will make sense when I hold the twin in my hand and look. Electricity generally makes sense but I have trouble when it gets to no neutral. There's a ground somewhere.

Thanks. My expert will wire the breaker properly since he can wire a house including 220 for a range. He will figure it out.