What's the 'whirring' noise that comes from the front?

[ls1ashley]

My DW noticed a noise that I had tuned out, but it's quite clear, and we are curious what it might be. It seems to come from the front of the coach, perhaps under the drivers feet or close. About every minute or so it's like something spins up and makes some sort of whirring sound.

This is on a class A rear engine diesel. The generator was off.

[slowmachine]

Many dash air distribution systems use air (vacuum) operated control flaps. There would be an electric vacuum pump that runs to maintain pressure in the system. If there is a leak, the pump will run frequently, until it dies.

[windsorbill]

I wonder if it's part of the dash air (condenser fan)? Possibly the fan is circulating the air through/over the coils, similar to the radiator for the engine, only much smaller.

[Bigd9]

My guess would be the condenser fan that is mounted right in front of the front axle in my Freightliner Chassis. Turn the dashboard air conditioner off and see if the noise goes away.

[Finance]

Yes, a/c condenser fan. An annoyingly loud design IMO. We spend big bucks to get the engine in the rear, and then a loud fan gets installed under the cockpit. There ARE quiet fan designs, if the designers of these systems cared enough.