There are several reasons why you might consider changing your AC unit now:

1. Age: If your AC unit is over 10-15 years old, it may not be functioning as efficiently as it used to. Older units can struggle to keep up with the cooling demands of your home, leading to higher energy bills and a less comfortable living environment.

2. Efficiency: Advances in technology have made newer AC units much more energy-efficient than older models. By upgrading to a more efficient unit, you could save money on your monthly energy bills and reduce your carbon footprint.

3. Repairs: If you've had to make frequent repairs to your AC unit in the past, it may be a sign that it's reaching the end of its lifespan. Continuing to repair an older unit can be costly, and you may find that it makes more financial sense to invest in a new unit instead.

4. R-22 Phase-Out: If your AC unit uses R-22 refrigerant, you may want to consider upgrading to a newer unit that uses a more environmentally-friendly refrigerant. R-22 is being phased out and will become increasingly expensive and difficult to obtain as time goes on.

5. As the newer refrigerants are introduced, most likely, equipment costs will be higher. 

Overall, upgrading to a newer AC unit can provide improved comfort, energy savings, and peace of mind knowing that you have a reliable cooling system in your home.