Funny issue with Aircon.

[Jocko]

It was particularly warm today so I dialed my Climatronic control down to its lowest setting (Lo) and it was working great. However, when I started to reverse into my drive the fan speed increased. I had to make a forward cut and it dropped a bit then went back up to high as I completed the manoeuvre. Was this a coincidence or is there some function that I don't know about? I know that if I have the wipers on and I select reverse the rear wiper comes on but I don't really see any advantage in increasing the amount of cooling (unless it is to stop you sweating if you are making a mess of the reversing).

[Breezy_Pete]

Select reverse gear and the A/C switches to recirculation mode.

Stops you breathing your own exhaust.

[MikeTheThinker]

Octavias (and I presume Fabias too) switch to internally recirculated air when reversing so as not to suck in exhaust gasses.  When they do it sounds like the fan rate has increased.

 

[MikeTheThinker]

3 minutes ago, Breezy_Pete said:

Select reverse gear and the A/C switches to recirculation mode.

Stops you breathing your own exhaust.

Snap!

 

[Breezy_Pete]

I believe in English English there are only two esses in gases. 

[J.R.]

Fan running faster during recirculation is one of the signs that the pollen filter is clogged or restrictive.

 

Even with a new one its a little faster on recirc.

[Breezy_Pete]

 It goes through the pollen filter in either mode on Fabias. Yetis too I think?

[MikeTheThinker]

59 minutes ago, Breezy_Pete said:

I believe in English English there are only two esses in gases. 

From a trawl of the interwebs and the OED it seems "gasses" is valid but deprecated in British English but quite prevalent in American and Australian English.

 

I've been doing a lot of proofreading for American authors so it seems I have become contaminated by immersion.  Time for a stiff upper lip

[J.R.]

1 hour ago, Breezy_Pete said:

 It goes through the pollen filter in either mode on Fabias. Yetis too I think?

 

Maybe it sped up on both settings after being changed then.

 

Which leaves the mystery why does it sound so much faster in recirculation mode?

 

It was an assumption on my part that when recirculating there would be no (additional) pollen or atmospheric pollutants to filter, that and the perceived sound of the fan running faster.

Edited 23 April by J.R.

[Breezy_Pete]

Acoustics of a big wide hole in cabin letting sound of fan motor out better?

Will be less pumping loss too, not having to pull through bonnet vents, so will probably run quicker also?

[MikeTheThinker]

16 minutes ago, J.R. said:

Which leaves the mystery why does it sound so much faster in recirculation mode?

Perhaps it's intake 'roar' as normally the intake is external to the cabin.

[Jocko]

Thanks to everyone for their input. I never thought of that answer. I keep promising myself I'll check the pollen filter but for my stiff old joints, it is rather difficult foe me to access. The next time I am in at the garage I'll ask them to do it.