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  #61  
Old 20th May 2019, 09:15 PM
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Goran Goran is offline
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Thanks

Did you change the setup from your original post where you had the new fan replace the old one on speed 1? And the old one still comes on speeds 2 and 3?
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  #62  
Old 20th May 2019, 10:36 PM
MikkiJayne MikkiJayne is offline
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Weird. I'm sure I posted that I'd changed it, but I can't find it now.

Yes, the original fan now comes on for 1 & 3, and the new one is 2. The electrical setup is much the same - I just subverted relay 2 instead of 1.
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  #63  
Old 21st May 2019, 09:01 AM
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Goran Goran is offline
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I'm still trying to work out how the thermo switch works.
So if speed 2 is requested does the relay switch of power to speed 1?
It sounds like at some point you have both fans working? Is this only when aircon is on requesting speed 1 of the old fan, and if the thermo switch requests speed 2 of the new fan (which is full voltage as it bypasses the resistor pack)

What happens if the instrument cluster requests speed 3 of the old fan? Will the new fan still be on at speed 2?
Is the limitation just the fuse? Together at max both will be pulling 48A?

Sorry so many questions

Last edited by Goran; 21st May 2019 at 09:07 AM.
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  #64  
Old 21st May 2019, 11:13 AM
MikkiJayne MikkiJayne is offline
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The fan speeds are determined by how much of the resistor pack the current has to flow through before it gets to the motor. Speed 1 goes through two resistors, speed 2 goes through one resistor, speed 3 goes direct to the motor.

The AC requests speed 1 by default, so puts current to the start of the resistor pack. The rad switch can also request speed 1, but is usually over-ridden by the AC.

The rad switch then requests speed 2 which puts current to the middle of the resistor pack, effectively ignoring speed 1. The start of the resistor pack is still powered, but as it has 12V on both sides of the resistor, no current flows and it is ignored.

In my car, speed 2 is disconnected from the resistor pack and goes straight to the new fan. When the rad switch requests speed 2 the new fan comes on (full) and the original fan keeps running at speed 1. Its like this simply to avoid having to run new wires to the engine bay - I have subverted the wire for speed 2 to drive the new fan, but if you wanted to run new wires you could have the new fan on, plus the original at speed 2. It doesn't need it though.

When the cluster requests speed 3 it puts current directly to the fan motor, bypassing the resistor pack completely and running the fan at full speed. In this situation, the rad switch would still be hot enough to be requesting speed 2 so in my car both of the fans would be at full speed.

Theoretically you could add a second resistor pack and a bunch more relays to have speed control of the new fan as well. That would be nice because it would run both fans slowly for AC when stationary, but its more hassle than its worth IMO, since I rarely sit in the car stationary wanting AC. I guess in London traffic that may be more relevant?

You could of course just put a bigger fuse in and run both fans in parallel, assuming the wiring would take it. You'd need to check the cross section and current capacity to be sure.
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  #65  
Old 21st May 2019, 11:24 AM
MikkiJayne MikkiJayne is offline
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Just checked - 6.0mm cable can carry 50A so you would be right on the limit running both fans. It has a 60A fuse, so I would be disinclined to try running both in parallel. Inrush current of 48A of DC motor will be way more than 60A.

It may be possible to get a 3-speed DC motor controller which you could use for the new fan, controlled by the inputs to the original resistor pack, but you'd still need to run wires in to the engine bay.
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  #66  
Old 21st May 2019, 12:55 PM
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Thanks Mikki for the detailed explanation.

I think I'll try connecting it up like you did.
Is it ok that when aircon gets hot and requests the old fan speed 2 it is no longer available? Just the new fan running at speed 1.
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  #67  
Old 21st May 2019, 01:07 PM
MikkiJayne MikkiJayne is offline
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The aircon can only request speed 1

Speed 2 is still available though - thats old fan at 1 and new fan at full. The total airflow is likely more than the original speed 2.
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  #68  
Old 21st May 2019, 01:53 PM
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Goran Goran is offline
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Thanks. Sorry I meant the air condenser switch, I thought it can request speed 2 independent of the rad switch? Track 45 in the diagram you posted. Is it possible for coolant temps to be below speed 1 so that the new fan is off, now the condenser can't request speed 2 of the old fan?

*edit* I get it now, it will request the new fan at its full speed! plus the old fan will be running at speed 1

Last edited by Goran; 21st May 2019 at 01:57 PM.
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  #69  
Old 21st May 2019, 02:12 PM
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Sorry one last question, I must be getting annoying by now
If both fans are working when engine is really hot and instrument cluster requests max speed of old fan, and new fan is already working because it was triggered by the thermo switch, isn't this both fans running in parallel?
Is the difference simply that one fan was already running so they are not both starting up at the same time so the current spike is less?

Thanks!
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  #70  
Old 21st May 2019, 02:52 PM
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Quote:
Originally Posted by Goran View Post
Sorry one last question, I must be getting annoying by now
If both fans are working when engine is really hot and instrument cluster requests max speed of old fan, and new fan is already working because it was triggered by the thermo switch, isn't this both fans running in parallel?
Is the difference simply that one fan was already running so they are not both starting up at the same time so the current spike is less?

Thanks!

The reason I ask is I'm not sure about stop-staring the stock fan (which is really old in my car) to cool off the engine at speed 1, I was hoping to have the new fan take that duty and take some of the pressure off. But as you said the new fan isn't sufficient for AC when the car is stationary. I guess what's needed is a dedicated aircon relay to speed 1 but that would require a lot of wiring.

Last edited by Goran; 21st May 2019 at 02:56 PM.
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