Bad smell coming from my heater vents

The heater and air conditioning draw outside air from the same vent at the base of the windshield, on the passenger's side. Selecting cold air, for air conditioning bypasses the heater core. Selecting hot air brings in air through both the air conditioner cooling coils (evaporator) and the heater core. If you have a cabin air filter, replace it. You might be able to get to the old mouse nest from there. If not, you'll need to remove the heater box cover, like you were going to replace the heater core to get to it. So follow the instructions in your repair manual for replacing the heater core. The one other, worst case scenario is if the nest is in the defrost ducts going to the windshield from the bottom of the dash. You may have to remove that ductwork if it's in there. One alternative is, with the heater box apart, use a wire coat hanger to fish the nest out of the defrost ducts. Once the nest is removed, visit your local auto parts store and ask for "Frigi Fresh" or a similar product. This is a deodorizer and disinfectant that will kill the smell once and for all. Hope that helps! Jim

A dead rodent smell is the worst, I got one in rig once and even after finding the carcass and cleaning up the smell still lingered, everytime it got hot, I finally bought a ozone generator and ran it for 2 weeks and that got all the stink out.