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Electric fan question.
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Ray White



Joined: 02 Dec 2014
Posts: 6286
Location: Derby

PostPosted: Sat Jul 02, 2022 12:14 pm    Post subject: Electric fan question. Reply with quote

I had a Kenlowe fan on my GT6. When I switched off, on a warm day, it would continue to run until the temperature had gone down.

Bearing in mind the higher temperatures associated with supercharger use, I thought perhaps it would be advantageous to have cooling air pushed around the engine bay after a run. This may be a mistake; I don't know.

Assuming the thinking is sound, the question then is how is it achieved.? Should I take the 12 v supply to 30 (relay contacts) from A1 on the RF95?

If I take the supply from A3 I imagine the fan will go off with the ignition?
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MikeEdwards



Joined: 25 May 2011
Posts: 2464
Location: South Cheshire

PostPosted: Sat Jul 02, 2022 6:42 pm    Post subject: Reply with quote

If the fan is temperature-controlled, that would suggest that wiring it to the permanent live would allow it to run after the engine has stopped until the engine is cool enough to shut it off. I think I'd like some kind of bypass switch to make sure it goes off, though. That said, my old Audi coupe would switch the fans on and off independently of whether the engine was running and that never caused any trouble.
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1976 Vauxhall HP Firenza, 1976 Vauxhall Sportshatch (x2), 1986 Audi coupe quattro, 2000 Audi TT
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Ray White



Joined: 02 Dec 2014
Posts: 6286
Location: Derby

PostPosted: Sat Jul 02, 2022 7:48 pm    Post subject: Reply with quote

MikeEdwards wrote:
If the fan is temperature-controlled, that would suggest that wiring it to the permanent live would allow it to run after the engine has stopped until the engine is cool enough to shut it off. ..... .


The fan is wired through a relay which may or may not have a permanent fused live supply depending which terminal on the RF95 is used. The fan would be thermostatically controlled while working but if the relay coil is connected to the ignition switch - as per the instructions - then wouldn't it stop as soon as the ignition was switched off?

A 12 v supply to terminal 30 should operate the contacts and (being positive earth with a diode inside the relay) a wire from terminal 86 goes to ground with 85 going to the ignition switch.

87 carries power to the thermostat. Another terminal on the thermostat sends current to the fan where a separate cable grounds it.
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MikeEdwards



Joined: 25 May 2011
Posts: 2464
Location: South Cheshire

PostPosted: Sun Jul 03, 2022 6:15 pm    Post subject: Reply with quote

Ray White wrote:
... but if the relay coil is connected to the ignition switch - as per the instructions - then wouldn't it stop as soon as the ignition was switched off?


If the switching wire for the relay is connected via the ignition switch circuit, it will only switch the relay when the ignition is on. If you connect it to a permanent live circuit, but the wires you are switching are connected to the ignition circuit, the relay will switch but it will have nothing to switch. So if you want it to run any old time, both the switching wire and the wire the relay is switching will need to be permanently live.
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1976 Vauxhall HP Firenza, 1976 Vauxhall Sportshatch (x2), 1986 Audi coupe quattro, 2000 Audi TT
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Ray White



Joined: 02 Dec 2014
Posts: 6286
Location: Derby

PostPosted: Sun Jul 03, 2022 7:10 pm    Post subject: Reply with quote

The fan fitting instructions say the switch should be wired into the ignition circuit ...so, presumably they don't expect it to run on. There is provision for a dashboard switch so I suppose I could do something with that; if I can figure it out.
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Sun Jul 03, 2022 9:46 pm    Post subject: Reply with quote

I guess the question is; is there a reason to accelerate cooling after the engine is switched off? If there are hot starting issues this would be a good reason, there may be other reasons? my modern has a fan that's sometimes on for a short while after turning the engine off.

Dave
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