Air conditioner blows hot air

check fuses and relays ---turn on system open hood if compressor is running check blend door for problem if not running possible low on freon , wiring /connection ,compressor damaged ---check switch ,fuses relays power to clutch [not when vehicle running ] and freon

Only way to tell if A/C Evaporator Core Orifice tube is plugged is by looking at A/C gauge readings , An if it is plugged you more then likely need a new compressor , they become plugged with metal particles from worn out compressor. Your best bet would be to take your vehicle to a qualified repair shop .

Could be a blockage in the ac system, or a blend door problem.

It may still be low on freon. It can hold several cans.
High side should be around 250psi and low around 35 or 45psi at idle if system is charged.
If you raise engine speed the low can drop below 20psi and switch off the compressor if the system is low on freon.
Could be a restriction in the system, bad relay, or bad a/c compressor-clutch.

1--BLEND DOOR NOT SEALING PROPERLY
2--FRONT CONDENSOR PLUGGED UP WITH DEBRIE
3--FRONT CONDENSOR NOT TRANSFERING HEAT (SPRAY WITH GARDEN HOSE WHILE ---RUNING SYSTEM IF IT WORKS BETTER CONDENSOR MAY HAVE TO GET CHANGED
4--WRONG CHARGED WEIGHT IN SYSTEM
5--COMPRESSOR CYCLE TIME NOT CORRECT
6--IF COOLANT CABLE VALVE ON SYSTEM MAY NOT BE CLOSING CORECTLY
---TRY PINCHING OFF THE COOLANT LINES TO HEATER CORE

I have a feeling that no one is checking the blend door in the plenum.

there are few things you need to check out:
1. if the compressor is overcharged it will shut down and you won't get any cool air
2. the thermostat for your cooling system is bad
3. the link to adjust the temperature is too short (did you feel the switch loose when changing temperature from hot to cold)?
hope this helps.

If it blew cold air after freon added and 5 days later blew warm, you may have a leak in the system. Also check and see if compressor comes on if not you may have an electrical issue, relay for compressor,coil on compressor, etc.......

could be your air blend door. It rotates between the heater core and the a/c evaporator to mix air. Temp knob or blend door motor is bad.

It is possible that the AC compressor clutch cycling is getting stuck in the off mode, this can be caused by a sticking expansion valve or a defective AC clutch control relay. One note u said u added more refrigerant to the system, if u over charged it you may cause damage to the compressor a $400 part and equal labor to replace, it might be a good idea to have the system charge checked by a shop that does AC work.