Deleting Auxiliary fan 'early 98 540i

[Silvercat]

This posting is related to my 2 earlier posts "540i viscous to electric fan conversion " and " '98 e39 540i Aux cooling fan "

I am going ahead with replacing the viscous fan. It seems, according to the manufacturer, that the new 17" fan will provide sufficient cooling without the aux fan and is in fact a 2 speed unit which is also designed to be wired to come on with the air con if that is what I wish to do.
The aux fan is open circuit on all connectors and will also not rotate freely. There is a 12v feed to one of the connectors when the air co is switched on - but that's it - nothing else. So why not get rid of it?

The main query I have is how the air con controller works - if the aux fan is not wired in, will this prevent the air con switching on?

Any comments on the possible foolishness of dispensing with the aux fan would of course be welcome

[Jeron]

The AC must have an aux fan running to operate properly.

I am not sure if the removal of the fan wiring will prevent the AC form switching on.

[Silvercat]

Originally Posted by Jeron

The AC must have an aux fan running to operate properly.

I am not sure if the removal of the fan wiring will prevent the AC form switching on.

Thanks Jeron,

I can wire up so that the e-fan, with which I propose to replace the viscous fan, has a feed from the existing auxiliary fan supply - a thought which occurred to me somewhat belatedly. The next question I suppose is why the existing aux fan has so many different speeds - I can only assume that it serves both as a cooler for the air con condenser (is that the slowest speed does anyone know?) and as additional cooling in the event that the main viscous fan does not cope e.g when ambient temperatures are high or under high load conditions - towing /climbing etc. e-fans as you have already pointed out are much more efficient than traditional fans - the one I am going to fit will pull about one cubic metre of air per second through the rad - which is just a number in isolation of course - but does sound to be quite a lot. And the supplier is basing his recommendation on the 540i cooling requirements with load conditions including light towing and discounting the aux fan as far as I know - but I can check that out.

[Jeron]

Your assumption about why the aux fan has two speeds is correct.

The problem with having only the primary fan is that there is not a seal between the condenser and the radiator so the primary fan will pull air around, rather than through, the condenser and not cool it properly.