When I start my car, the air coming from the AC smells like urine. What causes this and what can be done about it? Thank you.
My bet is that mass of leaves etc, that have fallen through the vent area in front of the windscreen is at fault. Try to clean it out and make sure the drain is functioning. Then turn the vent fan on high and spray a can of Lysol or a can of the special produce found at the auto part store, into that area.
You could also have a leak in the heater core, it usually smells like sour and stale curry. Try to see if the smell is equally strong with the HEATER on. If no smell, you would have debris or mould in your A/C ducts, as Joseph mentioned.
Make sure the A/C’s condensate drain is working (have a technician show you how to clear any obstructions), since standing water will create these smells.
The squirrels sleeping in the engine compartment are getting pissed when you start the car and wake them up!