1999 Dodge Caravan

Hi, is it just a musty smell like water that has been standing or a death smell? Many a mouse has died a terrible starvation in many a heater box, if it gets worse, it will have to come out(the whole unit). Ok They had problems with evaporator smells in earlier body styles but not any Caravans. See if the a/c drain on the fronr right of the firewall is not blocked, allowing water to build up inside, also look for little nutshells by the wiper right side cowl area where the air enters for fresh air and not re-circ. Ok good luck