Central vents blowing low & windscreen

[satbasi]

I've noticed the windscreen on my w140 will not demist unless I put the ac (windscreen button) on-it would demist before without using this. Also the cabin vents are blowing really low, hardly any air comes from windscreen-unless I press the recirculation button.

So I cleaned & replaced cabin filter under bonnet but no difference. Any suggestions?

 

[millo777]

I think there are 3 filters on the w140. The easy to access one under the bonnet, the recirc filter under the glovebox, and an activated charcoal filter which is a pain in the rear end to get to, close to the blower motor. Maybe that one is clogged?

 

[yojay]

The charcoal filter which millo777 is referring to is about £300 and afaik can potentially last the lifetime of the car. To test if this is this filter affecting your system, take it out and run the system to check for a improvement.

You can also use the diagnostics within the AC unit control panel, if you have a later W140 with the single din AC unit. There are plenty of post online about how to read the codes from it and do flap tests etc.

It's also worth making sure the fan motor that sits under the cabin filter that you changed, is in good working order, free from debris and spinning freely.

Would be interesting to hear how you get on!