How to switchfromAC to heat

nothing to do with the ac charge
the fan not running is a problem so check out the relays , fuses and temperature sensors that control that fan

It is a vent trying to close or open! There is a gear which opens and closes vents, I would say yours is shot! Most all vehics made in the last 10 years are bad about it! Not exactly sure what the part is called but it's a switch that goes to venting! Regards!

Low freon. Bad pressure switch, or compressor is bad.

Your AC switch is off. Anyway if the AC switch is on and the climate control is not flowing the cool or heat to any of the sides then it means that the AC nozzle is leaking and the pressure is just working into straight direction instead distributing to the switched position. It's a mechanical problem and not electrical at all

does the car have automatic climate control?

climate control requires the ac to work as well to vary the heat temperature and remove humidity from the cabin air. Check that the ac is working .

There is a blender that controls the air flow to go through the heater core for heat, and the evaporator for AC. It very well could be stuck.

You maybe able to try and get it to get unstuck by running the cars AC and switching from heat to AC back and forth and see if it gets unstuck. Just turn it on full blast and go from heat to cool.

If that fails, then you may need to service it. There should be a Lever Marked VENT under the dash, usually by the Brake and other pedals on the Driver's Side. Close the VENT and that will stop the Air from coming in and leave the A/C Blowing through the outlets(Vents).

I also read this online if you have an electronic climate control. "On climate control press off and heat button and let go quickly. Then press automatic. The display will start rotating eventually displaying a code 025,125 , 024 etc. Then press defrost to stop. You may hear blend door operating atb that time. It worked for my climate control."

MAKE SURE BLOWER MOTOR OPERATING IF NOT CHECK FUSE AND RELAY.ALSO CHECK HVAC FUSE THIS CONTROL HEATER + AC CONTROL SWITCH AND MODE SELECTION FOR OPENING AND CLOSING HEATER DOOR OR HEATER CONTROL VALVE AND AC+ DEFROST AIR DOOR.IF BLOWER AND HVAC FUSE OKAY.IF YOU HAVE MANUAL HEAT CONTROL MAKE SURE MODE SWITCH IS RECEIVING VACUUM. YOU HAVE TO REMOVE HEATER CONTROL SWITCH AND CHECK TO SEE IF GETTING VACUUM GETTING TO SWITCH LOOK FOR BROKE DISCONNECTED VACUUM LINES IN THE DASH AREA.IF YOU HAVE CLIMATE CONTROL.YOU COULD HAVE A FAULTY ELECTRICAL HEAT DOOR ACTUATOR.SOME CLIMATE CONTROL CARS HAS THE CLIMATE CONTROL PROGRAMMER HAS TO BE REPROGRAM BEFORE THE HEATER AND AC WILL WORK AGAIN.YOU NEED A DEALERSHIP SCANNER TO CHECK IT OUT.BUT IF YOU HAVE MANUAL CONTROL CHECK TO SEE IF YOU GETTING VACUUM.IF YOU GETTING VACUUM AT HEATER DOOR VACUUM ACTUATOR OR HEATER CONTROL VALVE EITHER ONE OF THOSE COMPONENTS COULD BE FAULTY.WARNING YOUR VECHICLE HAS AIRBAGS YOU HAVE TO DISARM THEM BY REMOVING FUSES WAIT 20 MINUTES BEFORE WORKING ON DASH AREA.YOU HAVE TO CRANK CAR UP TO CHECK TO SEE IF YOUR HVAC GETTING VACUUM.

Do you have rear ac and rear window defrosters if so the heater switch has failed. A GM priority diode unavailabe to any one but GM. Head to the local auto recyclers or pop for the $200 switch from your local GM dealer

You mean the blower doesnt work because if it was just the blower you would still have heat and ac, It would just take long time to feel the change because no blower is pushing it out. If thats the case check that you didnt blow any fuses under the hood. in the fuse block. Your owners maual will tell you what fuse goes where.
If the blower is working then you should have either heat or AC to some degree and maybe the blend door is not switching (jammed) or the climate control switches are broken or if you have Automatic climate control then maybe the module is broken. There is a Technical Service Bullitin on the blend door issue which entails replacing the hole box ( its called a Heater Manifold) which can get pretty costly if its that.