Try checking you cabin air filters. They could be clogged up with junk making air flow weak.
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?
a leak
The most common cause would be low refrigerant.
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
It's out of freon or refrigerant.
Max
about 5 minutes
diagram for 1999 chev subarban air conditioner
Hmmm, because it should?