C5 X7 Climate

[mooseshaver]

Not a fault, just a "why?"
With engine running and climate set to auto I've noticed the fan spins faster when in reverse, and slower in drive or neutral. This is when stationary after first starting.
I just wondered why. Nothing is wrong and climate control works fine.

[Hell Razor5543]

Airflow. When you are stationary or moving forward, the airflow hits the radiator first, so it should (in theory, at least) be cooled by that airflow. However, when you are reversing, the airflow passes over the exhaust, gearbox and engine before passing through the radiator, so it cannot shed heat as quickly. Hence the fans spinning faster in an attempt to keep the radiator cooler.

[mooseshaver]

Hello I don't understand. The car is stationary. Or are you saying because the intake vents work better in forwards the computer make the fan spin faster in reverse?

[Hell Razor5543]

Well, the fans and radiator are sited behind the radiator grill, so you have a fairly unimpeded airflow across the radiator. This means that, even when stationary, the fans don't have to work that hard to keep the coolant temperature down. When you are moving forwards the added airflow means that fans are needed even less. However, whilst reversing the airflow is back-to-front, and (unless something was done about it) this means it could be possible for the car to overheat. Hence the higher fan speed.

[mooseshaver]

Thank you for replying
And that goes for interior fan? That's what's speeding up.

[Hell Razor5543]

Well, the same may apply. The air intake is normally just below the windscreen. The outlets are normally angled to take account of the forward airflow as the car moves forward.

[mooseshaver]

Ahh thank you. I don't know how long I amused myself changing gear while waiting for the wife.

[Richard_C]

Could be that, but I think the C5 climate puts itself into recycle mode if you engage reverse, to prevent sucking in your own exhaust fumes which I guess might happen if reversing into a closed space like a garage. Try setting the recycle to something other than auto and see if it still does it.

I have yet to work out the exact conditions for auto recycle but think it does it in traffic jams, maybe even when you squirt the windscreen washers.

[mooseshaver]

There is supposed to be an air quality sensor too to detect fumes and moisture. Not sure I noticed it auto recycling or turning on air con in previous c5. Not driven this one far enough to tru