Wiring up an ''Emergency Switch" for the Fan

[DrewDude320i]

I have a Hayden fan in my car, and it needs an emergency switch. Just driving my car around the neighborhood for about 5 minutes, it got up to half way with no fan support. My plan was to run it through the rear defroster switch since my rear defroster doesn't work, and that way it'd look a little cleaner. Problem is, I'm worse with wiring than I am with women. Can someone help me figure out how to wire this thing up?

[g323]

I use one of these adjustable electric radiator fan thermostats:

http://americanracingsupply.com/cata...oducts_id=5282

[DrewDude320i]

I have one of those already. I'm trying to install this in case it breaks or if i am stuck in traffic and want it on all the time.

[g323]

oooo, Ive been thinking of this too,
if you have the same one as me, its got some wires coming out that arnt used-im thinking those are override relay wires, cross a couple and see what you get then take the wires that turn it on into the cabin and put a switch somewhere,,,probably you're already thinking along these lines let me know how it goes, i want to do the same

maybe without the relay just t-ing off the - + wires to the fan and brining them to the cabin would be better, then if the relay breaks you dont have to worry.

this is your only fan right?

i dont have to worry as much as i have my electic fan as a small(11in) pusher and kept the mechanical fan in the back-although i think it will become more useful when i do a 90% grill block

[tlapham]

It is easy, I used a spare relay i had laying around.
with whatever relay you have, find out which are the "switched" leads and which are the leads that will engage the electromagnet to make the relay switch.

1) Hook up +12 volts to one of the electromagnet leads.

2) hook up -12 volts to your switch, then from the switch, lead it to the other contact for the electromagnet.

3) Turn on the switch, make sure you can hear your relay "click".

4) hook up +12 to your fan, then hook up - 12 volts throgh the "switched" part of the relay. done!

[jrcook320]

You can run a wire off the factory fan relay. There is a wire that was part of the stock AC system that turns the fan on. I'd have to look at a wiring diagram to tell you which one, but it is in the center console. Go from there to your switch, then to a terminal on the fan circuit spade just behind the passenger side headlight.

You will need to install a diode in the line to replace the one that was part of the AC circuit or it may blow your heater blower fuse.

[g323]

jrcook320
Member
Join Date: Oct 2004
Location: Van Wert, Ohio
Cars: '81 E21 320i, '99 E46 323i
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You can run a wire off the factory fan relay. There is a wire that was part of the stock AC system that turns the fan on. I'd have to look at a wiring diagram to tell you which one, but it is in the center console. Go from there to your switch, then to a terminal on the fan circuit spade just behind the passenger side headlight.

You will need to install a diode in the line to replace the one that was part of the AC circuit or it may blow your heater blower fuse.

Please let us know how to do this, my car didnt come with the AC but i see that the wiring is there- looking forward to trying this out

[dhlthr]

You need to be careful that you design it so that you can't turn the fan on (by switch) when fan is already running. This could cause a short.

[AlaskaBimmer]

I just removed the wiring from the fuse box of a 320 and took a factory fan plugged it in and wired in a relay ran the wire through the fire wall and wired the switch end into a switched wire in the dash. I mounted the switch in that grill on top of the dashboard since it already had a hole in it the exact size of the toggle. Now I get "what does that switch do" all the time, and I tell them it powers the ejection seat....

My method is a totally manual way of running the fan, but when I'm in traffic I flip it on, when I'm cruising I turn it off. If I forget to turn it off it turns off when the car does....

my 323i didn't have a fan of any kind on it...I had several 320i fans laying around.....

[jrcook320]

You need to be careful that you design it so that you can't turn the fan on (by switch) when fan is already running. This could cause a short.

that's what the diode is for. Otherwise it will blow the fuse.

I'll look into it a bit further and pull the wiring diagram tonight. It's been 7 years since I've done this.

[GDAus]

Originally Posted by dhlthr
You need to be careful that you design it so that you can't turn the fan on (by switch) when fan is already running. This could cause a short.

that's what the diode is for. Otherwise it will blow the fuse.

I'll look into it a bit further and pull the wiring diagram tonight. It's been 7 years since I've done this.

Ummm .... What ????

an ordinary diode (yes there are more than one type!) is basically a one way valve for electricity .... and in this case ... it is used to isolate the A/C circuit from the Aux fan circuit.

Normally, the Aux Fan is switched on by a relay operated by a temperature switch in the radiator. The A/C takes advantage of this existing circuit by by-passing the temp switch to run the fan when the A/C is on.
The circuit that energises the electric clutch on the A/C compressor is connected to the aux fan circuit through a diode ....
so that when the A/C is switched on, the Aux Fan comes on too .....
but, if the A/C is off and the Aux fan is switched on by the temp switch ....
then the diode stops the A/C clutch being energised by the fan circuit too !!!

Also, providing that you wire a manual switch as a by-pass to the temp switch on the radiator, it wont blow a fuse if the fan is all ready on ! ... because it just connects 12 volts onto a circuit that all ready has the same 12 volts on it from a different circuit ... of course if you get the polarity wrong ..then that will certainly blow a fuse

[jrcook320]

Originally Posted by dhlthr
You need to be careful that you design it so that you can't turn the fan on (by switch) when fan is already running. This could cause a short.



Ummm .... What ????

an ordinary diode (yes there are more than one type!) is basically a one way valve for electricity .... and in this case ... it is used to isolate the A/C circuit from the Aux fan circuit.

Normally, the Aux Fan is switched on by a relay operated by a temperature switch in the radiator. The A/C takes advantage of this existing circuit by by-passing the temp switch to run the fan when the A/C is on.
The circuit that energises the electric clutch on the A/C compressor is connected to the aux fan circuit through a diode ....
so that when the A/C is switched on, the Aux Fan comes on too .....
but, if the A/C is off and the Aux fan is switched on by the temp switch ....
then the diode stops the A/C clutch being energised by the fan circuit too !!!

Also, providing that you wire a manual switch as a by-pass to the temp switch on the radiator, it wont blow a fuse if the fan is all ready on ! ... because it just connects 12 volts onto a circuit that all ready has the same 12 volts on it from a different circuit ... of course if you get the polarity wrong ..then that will certainly blow a fuse

It sounds like you understand the problem exaclty. When you remove the AC you remove the diode. I wired a switch that took the place the factory AC wiring. When the AC was switched on, it would bypass the switch in the radiator to close the fan relay and energize the fan. That's fine unless the fan switch is already closed, in which case it backfeeds 12v from another circuit and will blow fuse from wherever you pulled your 12v from. I pulled from the same wire the factory AC did, so it blew the heater blower fuse. The diode is a one way gate to prevent voltage from back feeding through your switch and blowing the fuse.

I'm now looking at a wiring diagram of the AC circuit. I don't have it in .pdf form, I printed it off from 320i.com a few years ago. I may just re-draw it in CAD so I can draw in the wires that need to be connected when you remove the AC unless someone else has it in pdf. When you remove the AC, you have to connect the large gn/br wire to the large gage gn/bl wire to retain power to teh heater blower motor (it runs through the stock AC blower switch. The fan switch is bypassed via that same circuit. Power flows from the blower switch to the temp switch via a small black wire. From there a small black wire runs to the AC compressor AND splits to a plug "T'd" into the fan switch circuit behind the passenger headlight. However, the diode is on the wire that goes from the compressor to that terminal. You can run a wire from ANY power source (though I think the blower is best since that's what the factory did) to bypass teh fan switch. This will close the fan relay and the fan will pull it's 12v across it's own fuse. But, without a diode on that wire you'll blow the fuse from wherever you pulled your power from as soon as the any automatic (factory or aftermarket adjustable) fan switch closes.

I have pictures and specs on the diode I used, and pics of where the T in the fan circuit is.

[dhlthr]

that's what the diode is for. Otherwise it will blow the fuse.

I'll look into it a bit further and pull the wiring diagram tonight. It's been 7 years since I've done this.

Yes I understand I was posting before I saw your explanation. I never did a switch on mine but I did wire so that it would run after I cut the engine off, this way if I ran into store the temp. would not spike up.

[DrewDude320i]

Josh,

That sounds a lot more complex than what I was looking to do. I just wanted to keep it simple and hook it up through the rear window defroster switch - looking at that switch, it has a green/blue (i think) wire, and a black wire, and then two little brown wires for the LED light. It would have been nice to just run it through there, since it already has a fuse allotted for it and the defroster doesn't work. But for whatever reason, that circuit isn't receiving power at all. So I guess that's a no-go. I'll probably end up buying a fuse holder and a 25 amp fuse, and then run the fan straight through the battery to the fuse and then to a switch.

[Layne]

Drew, I'll show you what to do. You don't have to have a diode, it doesn't need to be connected to the heater in any way.

[GDAus]

The easiest way to add a manual fan switch is to simply splice in a pair of wires to the Green/brown and Black/white wires attached to the temp switch on the left side of the radiator ..... run them into the car and attach to a switch. This simply energieses the normal fan control relay and takes power from the existing fan wiring. Doen't need heavy gauge wiring or a big switch .. the operating current for the relay is less than 1 amp.

I did this to my car over a year ago without any problems and certainly gives peace of mind when stuck in traffic on a hot day. ( I could have done it a few different ways since I've got about 22 years experience as an electrical engineer and technician ... but simple usually means reliable )

BTW .... JT has had the wiring diagrams from 320i.com hosted on his site for some time now ... http://www.jtresto.com/e21info.htm

and JR ... the circuit you described ... even if you still had the A/C installed ... the only thing that should happen without an additional blocking diode is that the A/C would come on (bypassing the thermostat control)... and since the fan and the A/C and the blower fans are all run of fuse 11 normally .. that should not blow the fuse ! .. unless there is another problem there somewhere.

[jrcook320]

hmm, well I'm certain you know more than I do being an electrical engineer. I'm a mechanical engineer that floated through 2 lousy "circuits" & "electronic devices" classes with a borderline useless professor that didn't know how to teach and tested easier than my 2nd grade math teacher (in other words, why study for the class when I had real classes to worry about?). lol.

Anyway, what you said to do is basically what I did, I'm pulling power from the same fuse (11) and sending power the exact same wire on the other side of the fan switch. The difference is, while yours looks cleaner on a diagram, the way I did it is cleaner in real life. I plugged into the existing 1.5mm gn/bn wire that's already under the center console and unused, then ran a single wire to an existing plug behind the passenger headlight. Both wires are a shorter distance than running 2 separate wires from the fan switch.

I'm not sure why I was blowing a fuse every time the stock fan switch closed while my manual switch was already closed. All I know is blew fuses until I installed a diode inline on my manual switch.

This is how I ran my wires after removing the AC:




inline diode:


stock AC fan bypass terminal:

[GDAus]

Thx JR for the info .... I'm a bit of a sucker for a good mystery ... and this business of blowing fuses got me intrigued. Over the years I've come across a lot of these sort of things where stuff just doesn't do what it should .. and I sort of collect them as curiousities. Certainly from your description and the diagram, there's nothing wrong with your logic .. so the circuit shouldn't blow a fuse, but it does ! a nice little mystery ... and how you've done it, is one of the ways I was thinking of doing mine until I found that the PO had cut out a chunk of the A/C wiring on my car.

Oh .. and I must admit, I do get a bit cold and analytical and focused when I'm problem solving, so appologies if I sounded critical in any way .. all my friends know to give me poke in the ribs to remind me to come back to planet earth when I get like that ... and the most important thing I've learned from experience .. is that for everything I know ... I still have a lot more to learn about everything else !

cheers

[jrcook320]

Oh .. and I must admit, I do get a bit cold and analytical and focused when I'm problem solving, so appologies if I sounded critical in any way .. all my friends know to give me poke in the ribs to remind me to come back to planet earth when I get like that ... and the most important thing I've learned from experience .. is that for everything I know ... I still have a lot more to learn about everything else !

cheers

I know all too well about that. I'm an engineer, I do the same thing. I've also realized that the more I know, the more I realized I don't know.

[pthm]

sorry to bring back an old thread, but curiousity, how reliable is the Aux fan

[DrewDude320i]

sorry to bring back an old thread, but curiousity, how reliable is the Aux fan

100% reliable. I've never had problems with mine. Gut that depends on the quality of the fan that you buy.

[meeky moose]

hmm, when i removed my ac i left my ac switch and wireing intact.. all ihave to do is turn the ac switch on and my fan comes on.. lol seemed easier than trying to wire in diodes, and other stuff.. and it runs my aftermarket fan just fine..

[pthm]

another "sorry for reviving dead thread" but, how big can I go on the fan, I am placing orders for parts so when I get back to the states they are all waiting for me to put them in

[bmac320i]

I have a 16" but dont think it will fit with the stock rad.

[jrcook320]

I know CJ was running a 16" as well. Not sure why the rad would matter if it fits in the core support. I can be mounted to the core support instead of the radiator.