when the a/c is on the smell of ammona is come from the vents

The evap core has some mildew and needs to be cleaned. You can try spray products that you apply to the air vents and the outside grill area at the base of the windshield. Have you been servicing your vehicle? You should have replaced your cabin air filter several times by now.

Hello i agree with Hal that the odor is coming from the evaporator core due to mildew and possibly the cabin air filters need to be changed.I had a customer last week who had a simular problem and also the air out of the vents was weak so we change the cabin air filter and all is okay and the smell is gone.HAVE A BLESS DAY from DR.RECO.