Your location?....size of home?...if you have been satisfied and comfortable with your 2 ton, it is unlikely you need a 4 ton AC condenser. Most likely your ductwork system could not stand the larger size without extensive modifications. Toss those dealers to the curb. Now if your current 2 ton is not able to maintain your thermostat setting, then that's an entirely different story.

keep in mind, you will need to replace your inside evap coil with a matching model.

IMO

E are in Charlotte NC, house is 2950 sq ft. We have been quite satisfied with our current unit and do not see a need for going up to a 4 ton. 2 different companies have given us the same info so maybe time to consult a third. They also want a dual zoning which we don't feel necessary either. I think extensive ductwork and/or wiring issues are quite costly. Thank you for your response

It this a one or two story home? Is the 2950 sq. feet the living space, or are you including things like the garage and basement?

Are you sure you currently have one 2 ton AC condenser?

one system or two systems?...I seriously doubt you have a single 2 ton system for a 2900 sq ft home. Post back complete model number.

IMO

First, if you have been satisfied with your current system, why would someone suggest doubling the capacity. It sounds like you may be working with "rule of thumb" guys that may be able to install equipment to "sort of" work. I would suggest talking to as many contractors as it takes until you find one you're comfortable with and can trust. If you are concerned about the capacity of your current system, you might want to consult a professional HVAC contractor that can do a Manual J calculation for your home. I've written an article dealing with this that may be helpful. If you would like to read it, please see it HERE. In that article I give an example of homeowners that had been suffering with an under sized AC unit and ducts for 8 years, but it tends to go the other way just as often. A manual J load calculation takes the guesswork out of selecting your new system.