that the nav display does double duty to display heat/AC options and data. See your owners manual. Sounds like your car could be low on A/C refrigerant.

Take it to a good A/C shop and have them check it. The $400-500 number from the dealer stinks. Unless the car is in warranty, go elsewhere.

If the car is low on refrigerant, you may have a leak in the system which will have to be corrected or you will keep loosing the refrigerant.