Air con bad smell on steep hills

Hi,

2002 Audi A4 Avant TDI (B6)

I've had smelly air con problems for some time. I had it cleaned and the smell went away for around 3 months. I then had a problem with the ECON light remaining on. This was traced to a bad sensor and the system repressurised and cleaned. The system has smelt fine for about 3 months but the "dead animal" smell has returned when I'm on a steep hill. Once I'm on the flat again a quick blast of cold air and the smell goes away.

I suspect that there is stagnant water trapped at the bottom of my chiller which sloshes around on steep hills. Just getting the aircon cleaned again won't fix this.

Does anyone know how to clean the chiller properly and also to check that the drain pipe is clear?

Many thanks,

Mark