I have a central a/c unit. The vents are small circles located in the ceilings. The master bedroom and den have no vents... I don't know why, or if maybe this is because there are rooms located directly above these two rooms. Can vents be installed? Can separate controls be installed so the air will only come in to the master bedroom? Thank you

Yes this can all be done(were there's a will there's a way,, and of course it may take some money and time too,, lol). This is going to be a hard one to answer without knowing your exact setup. Unit must be sized to take on the task first off. Then you will have to find a way to pipe registers to correct locations. Electronic dampers can be added to system to control these areas on demand. This can turn into a very large job, especially if all ductwork is concealed, and locations for new registers are hard to gain access to without tearing out walls, cieilings, or floors. I think your best bet at this time would be to get a few bids from differrent hvac contractors, and go with the one you feel most comfortable with. Like I said, its always possible, but the bill may make it unfiesable. If this is stictly for ac, and not for heat, then you may also look into mini split ac systems. Most likely save you money in the long run, and won't have to mess with existing system at all.

Are your vents small like 2 inch? If so then you should be able to get the spacepac vents into the rooms

Thank you for your helpful response, esp. the idea of a split system.
Yes this can all be done(were theres a will theres a way,,, and of course it may take some money and time too,,.lol). This is going to be a hard one to answer without knowing your exact setup. Unit must be sized to take on the task first off. Then you will have to find a way to pipe registers to correct locations. Electronic dampers can be added to system to control these areas on demand. This can turn into a very large job, especially if all ductwork is concealed, and locations for new registers are hard to gain access to without tearing out walls, cieilings, or floors. I think your best bet at this time would be to get a few bids from differrent hvac contractors, and go with the one you feel most comfortable with. Like i said, its always possible, but the bill may make it unfiesable. If this is stictly for ac, and not for heat, then you may also look into mini split ac systems. Most likely save you money in the long run, and wont have to mess with existing system at all.

No problem. Glad we would help. Let us know how things work out. Good day.