Have an 850 sedan with 99K miles. The blower unit (both in heat mode and AC mode) works fine in positions 1, 2, & 3. But in position 4, it simply shuts down.

My mechanic went thru the Volvo flowcharts and so on. No problems with "easy" things like relays, switches, fuses, etc. He's pulled his hair out and can't find the root of the problem. Of course, it makes it tough sledding when much of the search has to be done behind the passenger-side airbag! :)

Any thoughts? Anyone have this happen ?

Thanks!