Several thing scan cause a burning smell from a car A/C. One cause can be that the compressor is burning up. Another possibility is a wiring shortage.
Any smell from the car vents is unrelated to the AC system unless it is an antiseptic smell. Generally, the smells are environmental from your engine compartment, where the fresh air is taken from. If you smell something burning from the vents, then something is heating up to much under your hood. Check your compressor for a worn clutch, or oil leaking onto the exhaust manifold.
Burning wire insulation. Check and make sure there isn't too much voltage running through the fan wires.
if you have the ac on to long it starts to stink cause the filter picks up the smell and the smell spreads i suggest you get it cleaned
This normally indicates a refrigerant leak. STOP USING YOUR AC IMMEDIATELY AFTER THE ACKNOWLEDGEMENT OF THIS SMELL!! The fumes from the fluid in your AC system are highly toxic. The leak needs to be sorted out before the AC can be used again.
you have a bad heater core in your vehicle
leaking heater core
only when it is on, it causes slow acceleration
Possible that the ac compressor is locking up.
The balloon will eventually pop, and you most likely can find its pieces at the coil if using AC, or smell rubber burning if using heater.
it is probably the ac compressor locked up
Yes. get is serviced. The water under your car is nothing to worry about this is humidity extracted from the cars interior when the AC is running. The smell - no idea what this is if it comes from the AC itself then there must be some mold formed in the AC pipes etc.
My car had fish oil poured down it I used a product called What Odor? it completely eliminated the odor i recommend trying What Odor?