Having changed the cooling fan motor earlier in the year, I wanted to see if it was possible to prevent the new one from rusting up like the old one by giving the fan a little bit of "on" time on a regular basis.
Someone on here mentioned that some owners just add an override button, but being both a lazy beggar and inveterate tinkerer I thought I'd see if I could rig up something more automatic.
Here's what I've ended up with:
- new push-on/push-off binnacle button to enable/disable the automatic override
- this sends a 12V feed to a new module in the compartment under the steering wheel, next to the fuse box
- module consists of a couple of micro relays, a 40A relay to feed the fan, and a timer circuit controlling one of the micro relays
- the timer circuit runs the fan for ~ 1 minute after it first receives power, then cuts off
- the fan will also run if the ECM grants an earth in the usual way (because of A/C demand or heatsoak risk) - it's either/or
- the whole thing is wired into the existing circuits via an extension from the fusebox passing through the big rubber blanking grommet in the bulkhead
- I've also tapped from the fan feed back up to the binnacle to power a "proving" LED so I can check the auto-run is working as intended
Net result: cooling fan now runs for one minute each time the car is started, as long as the override is kept "enabled" by the binnacle button.
Hardest part was designing the circuit to control the time delay from power-on to fan-off. I initially tried a cheap off-the-shelf IC555-based circuit, but (1) I fried it with a wiring mistake on my first attempt and (2) the circuit didn't quite do what I needed anyway, which meant I had to add an unsatisfactory hack to the surrounding circuit to get the correct behaviour.
So for second attempt, I decided to build a custom circuit. My electronics is a bit rusty, but it seems to do the job. I used some scraps of Veroboard I had lying round, resistors I already had too, transistor I rescued from an old guitar amp, rest I picked up from Maplin.
Few more pics attached, also circuit diagrams in case they're useful to anyone.
Someone on here mentioned that some owners just add an override button, but being both a lazy beggar and inveterate tinkerer I thought I'd see if I could rig up something more automatic.
Here's what I've ended up with:
- new push-on/push-off binnacle button to enable/disable the automatic override
- this sends a 12V feed to a new module in the compartment under the steering wheel, next to the fuse box
- module consists of a couple of micro relays, a 40A relay to feed the fan, and a timer circuit controlling one of the micro relays
- the timer circuit runs the fan for ~ 1 minute after it first receives power, then cuts off
- the fan will also run if the ECM grants an earth in the usual way (because of A/C demand or heatsoak risk) - it's either/or
- the whole thing is wired into the existing circuits via an extension from the fusebox passing through the big rubber blanking grommet in the bulkhead
- I've also tapped from the fan feed back up to the binnacle to power a "proving" LED so I can check the auto-run is working as intended
Net result: cooling fan now runs for one minute each time the car is started, as long as the override is kept "enabled" by the binnacle button.
Hardest part was designing the circuit to control the time delay from power-on to fan-off. I initially tried a cheap off-the-shelf IC555-based circuit, but (1) I fried it with a wiring mistake on my first attempt and (2) the circuit didn't quite do what I needed anyway, which meant I had to add an unsatisfactory hack to the surrounding circuit to get the correct behaviour.
So for second attempt, I decided to build a custom circuit. My electronics is a bit rusty, but it seems to do the job. I used some scraps of Veroboard I had lying round, resistors I already had too, transistor I rescued from an old guitar amp, rest I picked up from Maplin.
Few more pics attached, also circuit diagrams in case they're useful to anyone.
