You can, but you'll have to check some things. The NEC requires that when more than 3 current-carrying conductors are located in the same conduit, that you de-rate the conductors. 4-6 conductors require de-rating to 80%.
This will be okay for your #6, because even at 80% it's good to 60A. But the real question will be whether your conductors for your air conditioner will still have enough capacity when de-rated. It's likely they're not.
Be sure that you use listed electrical fittings for tees.