Wiring up electric fan / Sensor switch.

jjl

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Joined
Apr 3, 2009
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I am just replacing my brass radiator with an aluminum one and have decided to use an electric fan as well.
The fan comes with a sensor that looks like it is meant to slip under the cable clamp on one of the radiator hoses or get stuffed into the radiator core. Neither of these ideas appeals to me as I want to note the engine temp, not the radiator temp.
Can I use some sort of electric sensor in the block that can be used to switch the fans on/off as required. Diagrams and details would be much appreciated.
Thanks
 
Like you, I did not like the probe in the radiator so went with a sensor in the thermostat housing. Initial version was a two wire with power running through the sensor. Replaced that with a single wire sensor that makes the ground circuit/connection for the relay - a better and more reliable solution.

This is the original for reference purposes.

efan1.jpg


efan5.jpg
 
Yes you can.

First of all, it doesn't matter a whole lot where you place the temp switch as long as it's on the hot side of course. When the temp is high enough to switch the fan on the thermostat will be open (unless failed) and as such you can put the switch in the ehad, the manifold, the thermostat housing or the rad (if a sensor port is available)

A typical setup uses a switch in the cylinder head. You can get those in nice weatherpack setups (Jet brand) and put the sensor in either head (pass. or driv. side). The switch switches ground for the switching side of a relay so you run a 12V fused (preferrably off the alternator) to that relay and then to the fan and a ground from the fan to the chassis. Another 12V ign switched is used to power the relay switching side.

2ztacdd.jpg
 
I run a Lincoln Mark VIII 2 speed fan. I have 2 constant duty solenoids to handle the amp spike on start. The low speed is key on, the high speed is either the cylinder head sensor or A/C turn on. I got a Bosch type relay to handle the positive/negitive issue with the temp sensor and A/C switch. Works good in southern AZ summer heat (115*). :bounce:
 
Great answers, thanks very much. I will buy the sensor/switch tomorrow and get it wired up. Air con is an issue as well for me so I will consider that as well.
 
Great answers, thanks very much. I will buy the sensor/switch tomorrow and get it wired up. Air con is an issue as well for me so I will consider that as well.

Then I hope you know what a diode is....as i'ts much simpler to wire with a couple of them in there off TT's diagram there....just two diodes, and take that temp switch to the top position where the switched wire comes in, hook that in series with that wire, ground relay wire it DID go ..to the car frame/chassis....

the two diodes take the striped ends, connect together, put that switch we moved to one unused end of one diode....take your a/c signal from the compressor clutch to the other diode unused end.....the two ends of the diodes with the stripes that we connected together...put to the relay coil where you +12 switched used to go....

I don't have a program to draw that up, sorry, but TT can, easy....
 
Do you mean like this pic. I modified (badly) the one above.
I presume this will also mean changing the temp switch to a two wire switch, is that correct.
Sorry if I did not draw the diodes correctly, I have no idea what their electrical symbol looks like, but I do know what a diode looks like.
Thanks very much to Twin Turbo for the images, it is much appreciated that you went to the trouble of drawing them.
RadFanSwitch.jpg
 
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Do you mean like this pic. I modified (badly) the one above.
I presume this will also mean changing the temp switch to a two wire switch, is that correct.
Sorry if I did not draw the diodes correctly, I have no idea what their electrical symbol looks like, but I do know what a diode looks like.
Thanks very much to Twin Turbo for the images, it is much appreciated that you went to the trouble of drawing them.
RadFanSwitch.jpg

Good to go....U got it....

:bounce::nuts: nice to know I too can tipe fyne tipe englush and get sometimes understewed....:bounce:
 
Sorry slight hijack but on the topic of electric fans:
- what size is the largest single fan that will fit with stock BB radiator? My memory says 16" but can't find anything to verify that.
- what size if 2 fans are used? 2x11" maybe?
- curved blades most effective?
 
Sorry slight hijack but on the topic of electric fans:
- what size is the largest single fan that will fit with stock BB radiator? My memory says 16" but can't find anything to verify that.
- what size if 2 fans are used? 2x11" maybe?
- curved blades most effective?

Slight variations to mounting, make that somewhat variable, but with two fans side by side, 11" like the Spals DeWitt sells, or off ebay, are about the largest you can do, I happen to love the rubber flappers that they have in the shrouds, that allow more holes for the air at speed , but when the fans are funning in traffic, they close for better fan draw....all other designs have limitations....

you can use dual 12" fans, one high, one lo staggered.....

I had a '87 vette fan mounted in my OEM '72 shroud, cut down, not enough fan, really, I know the radiator is 'marginal'....but it's stock for a '89 F body V8, which since it works there, really should be enough, worked fine in Maryland, but here in Florida it was always marginal in summer heat in traffic where air temps must be 140f off that pavement....

the '87 fan was ~16" but my '87 vette never had a issue with heat...again, something in the rad or ??....

:crap:
 
Just a heads up. My Vintage Air says specifically not to wire an electric fan as shown in the diagram with the diodes. They say it will damage the compressor, not sure why though or if that's true of all setups.
Anyway, they reccomend using a trinary switch which uses refridgerant pressure to cycle the compressor on/off and to turn the fan on.
 
Just a heads up. My Vintage Air says specifically not to wire an electric fan as shown in the diagram with the diodes. They say it will damage the compressor, not sure why though or if that's true of all setups.
Anyway, they reccomend using a trinary switch which uses refridgerant pressure to cycle the compressor on/off and to turn the fan on.

I don't see how that could be, but if looking at a GM schematic, you will find on a computer car, there is a diode across the compressor coil....I added on on my install 15 years ago with the TPI ...that line tells the computer to run the fans and increase idle speed/air intake for the compressor loading....
SO, that diode with the band end to the +12 and other to ground, controls/damps the inductive kick in the coil when the circuit is opened....

that is the ONLY possible item they maybe referring to that I can think of.....

no one ever bothered supressing that coil spike with older mechanical switch setups.....

:thumbs::smash:
 
My understanding with the trinary switch is that the compressor low pressure off is 20 psi, hi off 320psi. On mine this is between the relay and compressor.
The fan switch integrated in it is fan on at 200psi. This is wired so that the switch provides a ground for the fan relay. At hiway speeds or in cooler temps, there's usually good enough aiflow to keep it under 200psi. So the fan doesn't necessarily need to run all the time that the compressor is on.
Still not sure why they say tapping into the compressor clutch wire could damage it.
 
My understanding with the trinary switch is that the compressor low pressure off is 20 psi, hi off 320psi. On mine this is between the relay and compressor.
The fan switch integrated in it is fan on at 200psi. This is wired so that the switch provides a ground for the fan relay. At hiway speeds or in cooler temps, there's usually good enough aiflow to keep it under 200psi. So the fan doesn't necessarily need to run all the time that the compressor is on.
Still not sure why they say tapping into the compressor clutch wire could damage it.

Yeh, I finally fished around and d/loaded Adope's reader, and so looked at that file/page.....I see no reason for the added complexity, other than some solid state setup in their a/c controller would not be happy....it wonder if it's related in design to that super finickey crap that guy sells that is a variable speed PWM controller for car cooling fans....BASKIN that's the guys name....

:shocking:
 
Don't know where you are located, but if it's in an area where you use it a lot then having the fan on the condenser all the time when the a/c is on is very beneficial. Here, in S Florida we use the a/c almost everyday all year and that is the way I do it on all my vehicles. And running the fan has absolutely nothing to do with the engine cooling, at least in purpose.


Mrvette is probably correct in his assumption
 
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