Smelly air conditioning in car

[alancohen]

I used the air conditioning in my Peugeot 405 for the first time this year the other day and it smells like there's a dead rat in the engine (well something that doesn't smell too good anyway). Any ideas? (Other than the dead rat that is.)

[jbeputnam]

It depends on how long you've owned the car as to whether it is your fault it has happened or not. In the winter, it is important to run your air conditioning every now and again to stop it doing what has happened to you. The system can go all nasty, as you have unfortunately experienced.

Solutions: Run it for a little while to attempt to clear it through. Either that, or take the car to the dealer to be looked at. The problem may not be just down to that.

[Heywood]

The smell is likely to be just mould, try spraying some air freshener into the air intake (for the heater only) it is under the glove box up in the pasengers side footwell. You could also try spraying the vanilla fridge freshener deodoriser. This might kill some of the mould.
Air conditioning units need to be run at least once a month even during winter. This helps to keep the compressor lubricated. With the heat setting on, they are very quick way of demisting your car in winter as it dries out the air.
One last thought is that the air conditioner drain may be blocked and any condensation is not draining away and so probably rotting your carpets. It the drain is working, there should be drips of water coming out from under your car when the AC is on. Make sure its a humid day when you check.