Try checking you cabin air filters. They could be clogged up with junk making air flow weak.
I have a 02 buick rendezvous mine would blow a lil heat but never would get hot. We had it checked it was the thremostat, that is what was wrong with mine. They told me there is three things it could have been , it could be low on antifreeze , thremostat, or if you have to keep adding antifreeze often then it is your heater core.
An air conditioner blows out heat
no but it may depend on the conditioner
Portable air conditioner will not blow cold air. What to do?
The most common cause would be low refrigerant.
a leak
The vacuum supply line from the engine is disconnected or broken. When the vacuum supply is cut off the system defaults to the defrost mode.
Not likely
about 5 minutes
It's out of freon or refrigerant.
Max
diagram for 1999 chev subarban air conditioner