Changing from rad fan switch to ecu control

[ben7]

A wiring question please:

I am looking to swap the coolant fan control from the radiator fan switch to an ecu control.

I have sorted the ECU side of things, but I need an idiot guide to the wiring please.

The current cabling goes like this:

Green (12+ ignition) --> Rad fan switch --> green/black --> fan --> black (earth)

The (emerald) ecu sends the following from Pin 6: 'output swtiches to earth to activate relay and fan'

So where/how do I wire this in to make it all work then?  

Ben

[Jonathan Kay]

AMENDED

Do you want a manual override?

Expert advice, please: is it better practice to use a relay to use that switched earth to switch the feed or to make the feed permanent and switch the fan earth?  (I can work out the wriing either way.) And if the latter should you add a relay?

Jonathan

 

[ben7]

Ha!  I can't believe how obvious that is now you've said it!  I've had my head under the bonnet for 9hrs today and have obviously reached the point where I can't see the wood for the trees (too tired to think of a witty pun on that).

Thanks JK  .

There is no relay in the circuit atm; as you say it runs from ignition to Fuse 3 straight to the fan control switch to fan to earth.

[ben7]

I also preferred your first answer before you edited, I understood that one  

[Jonathan Kay]

I've just had second thoughts... but the principle stands.

;-)

Jonathan

 

[ben7]

If you were to add a relay into the circuit, how would you do it then?  Unfortunately I can't work out the wiring...

[aerobod - near CYYC]

You will need a 4-pole relay such as this: http://www.halfords.com/motoring-travel/tools-diy/fuses-electricals-fixings/halfords-hef554-relay-12v-30amp-4-pin . Also add an inline 30A fuse to the 12V line from the battery if it doesn't go through the fuseblock. The 4 poles are connected as follows:

Pole '85' to ECU output

Pole '86' to ground

Pole '87' to fused 30A battery supply

Pole '30' to fan.

I would use a minimum of 14 gauge wiring to the fan and battery and 24 gauge to the ECU and relay ground. Standard insulated spade connectors will fit the relay poles and the relay can be attached with a screw or body mounting tape in a convenient position. The ECU output will need to be a positive voltage of at least 200mA and 5V to trigger the relay.

[Paul Deslandes]

Aerobod, the ECU switches it's control output to ground so your arrangement needs modifying.  Relay pole 85 should go to ECU o/p and 86 to the ign switched +12V.  The other fan wire will need to be grounded as well, but you knew that!

I would always advocate using a relay for a fan or any other motor control to avoid voltage switching transients damaging the ECU electronics.  The outputs are protected but a good old cheap relay adds security and also makes sure that too much current doesn't flow through the ECU o/p.

[Jonathan Kay]

Any preference for using that relay to switch the feed or the earth, Paul? (That's why I removed the wiring plan last night!)

Thanks

Jonathan

[Paul Deslandes]

Convenience I guess, and maybe a bit of electrical safety as it isolates the supply, if you switch the +12V feed.  Otherwise it doesn't make much difference. 

On the other hand, if adding an override switch, it's easier to switch the ground as it only needs a single wire to go from the fan -ve to the o/r switch, the otherside of which can be taken to any convenient local chassis point.  The o/r switch and relay contacts being in parallel and 'OR'ed.

Paul

[Jonathan Kay]

Thanks, Paul.

Got all you need, Ben? 

Jonathan

[ben7]

Thanks all.  I can crimp spade connectors on the correct wires and connect them to the things I'm told to, but unfortunately I don't understand electrics (relays!) enough to be able to determine from those two posts what I need to do!  

I think:

85 - ECU (switched earth)

86 - 12v ign

87 - ? ground?

30 - fan?  Does this power the fan?

Like the idea of an over ride switch but don't understand how it would over ride the ecu switch unless it is in the ECU --> 85 line so you could switch the earth on regardless of the ecu.  Leave the o/r open and the ecu would tell the relay to earth to turn on the fan.  Close the o/r switch and the circuit earths turning the fan on.

Separately I understand that an o/r on the fan's -ve would work if there wasn't a relay/ecu control.  Is it best I don't worry about trying to understand it and do what I'm told? 

Ben

[Jonathan Kay]

Is it best I don't worry about trying to understand it and do what I'm told?

Not for my students, it isn't! :-)

With the override switch (which can be fitted later) let's go with the switched earth option.

The fan will have a permanent feed (igntion-switched and fused) which is your current (!) green connected to the fan without the switch. It will have a switched earth which can either be made by the ECU feed (via the relay) or the override switch. This will replace (but probably be a modification of) the current permanent earth which is your black.

Now ignore all of that for the time being and read "Understanding Relays". You won't need most of it for your purpose. but it will help you get your mind round the controlling side and the controlled side. (The pin numbers in the article won't match the relay you use.)

And... you do have a multimeter?

Jonathan

 

 

 

[Paul Deslandes]

Only change to your list is 87 goes to +12V via a fuse, not ground.

Yes, 30 powers the fan.  As originally described, the process is:

ECU detects high temperature and switches its fan control output to ground. 
You now have relay 86 at +12V and 85 at ground (zero)
This energises the relay and makes the contacts between 30 and 87 close, i.e. join together, allowing current to flow from the +12V on pin 30 to the fan motor via pin 87.
The other motor wire is connected to chassis and completes the circuit.

The idea of the override switch is to parallel the relay contacts (30 and 87) so that, when closed, the switch makes the circuit even if the relay hasn't been energised by the ECU.

I'm concerned about confusing you with the next bit, always assuming you're still with me, so I'll try and be clear.

An alternative way of controlling the fan is to connect the +ve terminal of the fan to +12V via a fuse, rather than via the relay as above.  Instead, you put the relay in the path between the fan's -ve terminal (wire) and ground.  This has an identical effect as it makes/breaks the circuit to control the fan, just in a different part of the circuit.  The advantage of doing it this way is that you can take a single wire from your O/R switch to the fan -ve terminal and the other switch terminal to any convenient chassis point.

Re your point about putting the switch on the ECU side of the relay, best not as it reduces any chance of damaging the ECU.

Paul

 

[Paul Deslandes]

Sorry, I'm getting confused myself and have interposed 30 and 87 which, for practical purposes doesn't matter as they are interchangeable but is probably confusing.  I'll edit the seconfd piece so it's consistent.

I've done a quick diagram which will hopefully help make things a bit clearer.  I'd post it if I knew how to include an image on a thread.  Help!

[Jonathan Kay]

I'd post it if I knew how to include an image on a thread.

Uploaded from your computer or linked to a picture on a hosting service? Ian B's helpful Guide.

Jonathan

[Paul Deslandes]

I hope this helps

Paul

[Paul Deslandes]

If all else fails, read the instructions.  Is it legible?

[ben7]

Ah, so with the o/r switch set up you make two connections from the same fan -ve.  Yep understand that now.  Well I understand how the o/r switch now works.

So if you were to place the relay in front of the fan +ve (which would now run from 30 on the relay) you would have two fused ignition 12V+ supplies at 86 and 87?

How would you connect the relay if it were downstream of the fan and connected to the fan's -ve then? (please tell me which pin connects to what)

JK yes I am the proud owner of a muiltimeter (but not clever enought to be a student of yours I'm afraid  ).  The engine is a mish mash of original car loom, k series engine loom, ford puma engine loom and emerald loom.  It has been a long hard slog to get where I am, but I now have a design for a shiny new Emerald loom and just need to figure how it all goes together.  The fan question has resulted from this new loom and generally trying to tidy everything up.

It all currently looks like this  :

[Paul Deslandes]

Hopefully the diagram should answer your question. I guess our posts crossed.

If not clear, shout.

[Paul Deslandes]

Might be a bit clearer with larger font

[ben7]

Makes perfect sense.  I can do pictures  .  

I appreciate all of the help guys.  I am sure that there will be more silly questions to come...!

[ben7]

Well all wired in and it works!  Well the o/r switch does as I can't check the ecu as I have a problem... 

Seeing as the electrickery gods have read this thread, I'll take my chances and post it here...

New loom has arrived from the ever helpful Emerald.  It is a standard affair with the ECU and Fuel pump running via two individual relays integrated into the harness.

Putting aside the myriad of wires everywhere else for a second (it's relatively straightforward plug and play), if I connect the +12v ign 'in' on the loom to the +12v ign on my car, turn the ignition on, nothing happens.

If I touch the +12v ign 'in' on the loom against my battery, the Main Relay clicks, but the fuel pump doesn't start up (it always used to when I turned on the ignition) and there is no light on the ecu (I'm sure it's red when just ignition, green when engine running iirc - it's been a while).  

Sadly my fuel system is in pieces atm, so I can't start the engine, but I am puzzled on a number of fronts:  

Why does the relay not engage on the ignition from the car?

Why does the relay engage on the battery, but not start the fuel pump?

Incidentally if I connect the (yellow green) fuel pump wire directly to the battery, then the pump spins up.

Volts across the battery are 12.4v, volts coming out of the car's ignition wire only 11.8v.  Could the voltage drop be the (main relay) problem?  (still doesn't explain the fuel pump tho...)

Both relay fuses have been checked and are seated correctly...

[Paul Deslandes]

The main relay won't notice the drop in voltage and should operate ok with 11.8V, and a lot lower than that.

Is the +12V ign on connection at 11.8V when the ECU wire is connected or disconnected?  I'm suspecting that it drops dramatically as there's either a fault with the switch or a fuse has gone (comment re fuses being ok noted though). This would also explain the small but significant voltage drop that you're seeing.  Check that some of the wires haven't come off the back of the ignition switch.

I assume there's a battery connection to the loom, is this ok and are all the ground connections made?

I'm not familiar with the Emerald ECU or its loom so can't comment on the particular wiring or colours etc but I'd check that everything is as it should be.  Presumably, when you touch the ECU wire to the battery, the fuel pump relay doesn't click.

It's really hard to diagnose remotely but my first call would be to make sure all the connections are made, particularly to ground (chassis) and the battery.

Paul

[Shaun_E]

Would one of you please write the solution up into a short document with the wiring diagram. Email to me (shaun dot elwell at lotus7club dot com) and I'll add it to the technical guides section of the site.