When you removed the ac components from the donor, was the freon still charged?

If not, the system has a leak.

Assuming you have a R12 system, what I would do is buy the R12 to 134 kit, for $40. (Walmart is usually cheapest) It comes with the adapters for the fittings, a pressure gauge, and 2 cans of freon. I would suggest you substitue one of those cans for one with UV dye mixed in. Those are about $12. Charge it up, and you should have working A/C. Use it for a week or 2, and then go rent a UV kit from Autozone, which will be a UV light and glasses, and check for leaks. Fix the leaks and then re-charge.

Worst case scenario is you buy the $40 recharge kit and it wont blow cold air. But you might get lucky and everything works fine. Could even be a slow leak and you have to charge the system every year.