The way the system works is that to get half speed the 12 volt feed is sent through one fan and then into the next using the RAD FAN (AC) relay only. To get full speed it uses the RAD FAN (engine) and FULL/HALF speed relay. I know that this does not tie up with how the system works but this is how the Lotus Wiring Diagram works
When I get issues like this I take the covers of the relays so I can see if they are operating as they should. I can then also over ride the relay by manually closing the contacts.
If you have the Elise cooling system then you will not have the third Full/Half speed relay.
On the Exige system you can not have just one fan working on half speed as they are wired in series.
I have had the relay box apart. all 4 relays are present. manually closing one of the relays switches both fans on slow, closing another relay results in one fan on fast. closing the three fan related relays simultaniously together result in both on fast.
just as the circuit diagram suggests should happen…
So the only reason I can think of why the car operated with only one fan at full speed is that the ecu does not ever provide the signal for the low speed.(which is required for both slow speed and both on full operation.)
I have not had time to remove a seat and try and test this signal from the ecu, this should identify whether there is a wiring issue after the ecu or whether the ecu is just not giving a signal.
i have however added a little wiring and spliced into the two switching wires on the controller unit. now i have a manual override switch to put both fans on slow or fast. so traffic is no longer so stressy for the driver, it is just nice to keep the temps at 80 degrees even in traffic. keeps the car and contents cooler
Mitch - dont remove seat and stuff - just test the wire at the relay box ? Yeah except you dont remove the possibility of a damaged wire of course, which is also quite possible …
To save others some time the fan relay module can be found on the front off side wheel arch liner. Contrary to many guides which show pictures of the main relays for the horn etc which are on the near side!
I lost many hours yesterday removing the main fuse and relay boxes and replacing all the corroded fasteners. Only to discover that you don’t actually need to remove the fuse/relay boxes to fit a fan switch!
