most likely your thermostat may be not woriking or I believe your heater core may not be closing and opening ....guess would be to replace thermostat its cheap and easy to do....not sure what air conditioning would have to do with what you were asking.
You should check your blend door. It isn't moving and this is causing the air to only blow hot. Can be either a sticky door that when moved may free up and be ok, or may need a new actuator, these are electronically actuated. Access through the engine compartment on the passenger side of the engine compartment.....there will be an area where to make a cut on the firewall area of the plenum to access the blend door and actuator.
It could be that your air conditioning system is not operating under the hood. OR, it could be a temperature control issue in the dash.
Do you hear the compressor cycling under the hood when the AC is set to the on position? It will click on and off from time to time. If you can follow the metal lines and hoses from the AC compressor, you can feel them to see if they get cold.
If it's a "no" to both questions, have your air conditioning system checked for proper charge and electrical operation.
If it's a "yes" to both questions - then have the temperature control mechanisms in your dash inspected.