jwillman

Got my dual electric fan in and wired. The Hayden dual fan controller neeeds a switched ignition source to turn off the fans with the ignition.

I thought tap into switched power wire to the AC fan but when that AC fan kicks on the voltage drops to zero.

Any ideas on what I am doing wrong or on a better and easily accessable switched source? What about the 14 pin connector?

FredR

Jim,

The trick is to have a relayed" connection with the power supply generated from the live voltage post under the hood. Spal do a neat kit for this purpose with most of the wiring harness needed they also do a temperature controlled kit as well. Your problem then reduces to one of having a voltgae supply to energise the relay. Not familiar with your early model but I am sure plenty of listers will make useful suggestions.

I do recommend fitting a temperature controlled unit of some ind. It is not too difficult to do this and there is little point in running the fans if they are not needed.

Regards

Fred R

FredR

Jim,

Apologies- I may have misunderstood your query if the item you refer is a controoller in its own right.

Good luck with the installation

Fred R

Alan

The AC fan must have 12v across it to run - I think you need to re-measure this - what you are seeing is the opposite of what you's expect - make sure you have the meter connected to a good ground...

Unfortunately there actually aren't many places where you can find ignition power in the engine compartment - it mostly doesn't go there (I know that seems weird...)

Alan

Bill Ball

For a similar situation (intercooler fan relay) I could not find a switched power source in the engine compartment, so I ran a wire from the CE panel through the firewall with the harness and up along the top of the inner fender. I no longer have the intercooler, but I left the power source wire there for future projects. None of the pins in the 14-pin connector are ignition switched power. My reading of the 14-pin connector from 85-on:

Alan

Bill on a '79 the Aux AC fan is relay fed controlled only by the X bus - so its basically like an ignition supply - this is not true of most years of course.

This is the right place to look, and if the existing AC fan work this should be viable.

Alan

jpitman2

I use the original ac fan power to pull in the left fan of my 2, and then fire the relay for the right fan from the first fan power.
If you find the +12V lead going to the temp sensor low in the rad front left that will be ign switched power (ie NOT the brown one),but I think its only light current rated to fire the fan relay. Use either the original AC fan power supply, or the hot point via a fuse.
jp 83 Euro S AT 53k

jwillman

I have located the bl/gn wires at the temp switch at the base of the radiator. According to the wiring diagram they are 12v switched. I get 12V at that terminal with the ignition switch on.

When I jump the bl/gn to the br ground wire (simulating temp switch closing) the AC fan runs but voltage at the bl/gn wire drops to zero.

What am I doing wrong? I would have thought I should see a constant 12V whether the temp switch was open or closed (jumper installed or not). Am I missing/ forgetting some basic electrical system understanding?

dr bob

Jim--

The wire to the switch has a relay coil between positive and where you are checking. The brown wire is ground, relay coil is a resistor. When the temp switch closes, the blue/green wire is pulled to ground. Now there is potential across that relay coil, which closes the contacts and sends power to the existing fans. With the temp switch closed, both sides of the switch are at ground potential.

****

Many folks use digital meters to test for voltage. The meters are very high impedance devices, and consequently put very minimal load on the circuit under test. Good for delicate solid-state circuitry, not quite so good for old-fashioned relay logic stuff. Problem is compounded somewhat by the tendency to use a switch in the ground side of a circuit. This is generally not good practice, but it makes sense in certain situations like this, since the exposed wiring in the engine bay is not connected directly to battery positive. If a sense line is accidentally grounded, worst case is the relay triggers and the fan runs. Switching power means you need to run two conductors to the switch, and also protect that sense wiring with a separate fuse. There are always too many wires and too many fuses in a car, per the accountants and the assemblers.


Back to the original discussion...

jwillman

Thanks Dr. Bob.

So this sounds like I will need to go inside the cabin to the CE panel to get a pure constant 12V ignition switched power source?

Any ideas on cleanest way to do that on a 79?

jpitman2

Jim,
You can ONLY use the +12V going to the temp sensor if you DONT use the temp sensor as well, because when the sensor makes circuit, it grounds the +12V to fire the internal relay. I thought you wanted +12V to run the new fan controller, which had its own temp sensor - this will work if the lead is disconnected from the original sensor. If my understanding is wrong, then I misunderstood your plan, for which I apologize. If you wish to keep the original sensor connected and doing something (no point otherwise), then you will need a new switched source of fused power.
jp 83 Euro S AT 53k

Alan

You don't want the temp sensor wire from the coil you want the fan driver wire - the ouput of the relay - where is that?

Alan

jwillman

Alan,

If your talking the main power wire to the AC fan from the relay then my duals would only run when the temp switch or ac temp switch tripped the relay to run the AC fan. I am hoping to have them operate independant of the AC fan operation.

Alan

So add a new relay in the engine compartment for the AC fan if you are keeping it (use the existing AC thermal switches in the coil connection for the new one).

Simply connect the coil connection of the existing CE mounted AC relay directly to ground - it will be on whenever the ignition is in accessory or ignition position (but off for starting)...

Alan

I pretty much assumed the new fans would replace the existing AC fan - then you'd need this new X-bus trigger and to adapt the AC temp sensors to be additional triggers depending on what your new fan controller supports - e.g. you may need to rewire the sensors however needed...

jwillman

I looked for any solid 12V wiring from the X circuit into the engine compartment. Looks like the winshield wiper has a 16AMp protected circuit wire that goes from X circuit thru a fuse direct to the wiper motor.

Any issues with tying into that wire for the fan controller?

Thanks.