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Old 11-07-2012, 10:16 PM   #1
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Default Wiring Guru's...A/C Switch Wiring 12v or GND.?

I'm trying to recycle the A/C switch in my climate control unit, to control my 2-speed electric fan.

The relay needs a GND (-) to trigger each speed...

By the looks of the diagrams, the connector, back of the Climate Control Unit, has 2 wires that run through the A/C switch...

Solid Blue...Switched 12v from Wiper Fuse
Green/Red...from switch to A/C unit...

Referenced from here...

http://www.madracki.com/miata/images/wiring/95sys.pdf

So, it's 12v running through that switch?

Plan is to snip it, and run the blue wire, from the Climate Control unit, to GND....

And run the Green/Red to my e-Fan relay.

Also, is there a illumination to the switch, with it on?

I suppose I'll need to change that from GND to 12v, if I want it to work.
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Old 11-07-2012, 11:47 PM   #2
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The solid blue wire only delivers power to the bulb which illuminates when the A/C switch is engaged. That bulb will probably prevent sufficient current from passing to operate a relay reliably.

Green / Red does give a direct closure to ground (through a blocking diode) when the A/C button is depressed, however it also goes through the blower switch, and thus, only conducts when that switch is in a position other than "off".
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Old 11-08-2012, 01:22 AM   #3
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Quote:
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The solid blue wire only delivers power to the bulb which illuminates when the A/C switch is engaged. That bulb will probably prevent sufficient current from passing to operate a relay reliably.

Green / Red does give a direct closure to ground (through a blocking diode) when the A/C button is depressed, however it also goes through the blower switch, and thus, only conducts when that switch is in a position other than "off".


Okay, so there's already constant 12v to the bulb? SCHWEET!

Where does the A/C switch get it's ground from? Through the climate control unit?

Or is it the green/red wire, I'll need to send to constant ground, and another output I'm still hunting?
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Old 11-08-2012, 01:27 AM   #4
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Quote:
Originally Posted by mylesofsmyles View Post
Where does the A/C switch get it's ground from? Through the climate control unit?
It goes to ground through the blower switch, as I said before. The blower switch, in turn, goes to ground through the black wire when it is in any position other than off.



Quote:
Or is it the green/red wire, I'll need to send to constant ground, and another output I'm still hunting?
Huh?

I'm still really unclear as to what you're trying to accomplish. If you want to use the A/C pushbutton to trigger some external relay, it will only work when you have the interior blower on, unless you tear the HVAC control panel apart and modify it.
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Old 11-08-2012, 10:51 AM   #5
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I have so many questions, that im not going to bother asking.
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Old 11-08-2012, 12:32 PM   #6
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Originally Posted by Joe Perez View Post
It goes to ground through the blower switch, as I said before. The blower switch, in turn, goes to ground through the black wire when it is in any position other than off.



Huh?

I'm still really unclear as to what you're trying to accomplish. If you want to use the A/C pushbutton to trigger some external relay, it will only work when you have the interior blower on, unless you tear the HVAC control panel apart and modify it.


It's simple....

I'm using the 2-Speed e-Fan Relay that Volvo uses in most of their cars, from early 90's on.

The relay gets constant 12v from the battery, with a fuseable link.

The fan gets constant ground, and a lead to the relay for low & for high speeds.

The Relay gets two separate inputs....a ground for low speed and a ground for high speed.

Low speed is controlled via a SAAB temp sensor in my LOWER Radiator hose....one ear to ground, the other to the relay, so when it hits said temp, it grounds out, and the fan comes on.

As a back up, I want control of the high speed, via the cockpit, hence the A/C switch.

So The A/C switch sends out ground, which is perfect. But I'll need the heater fan on at least #1...no biggie...

I can live with THAT.
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Old 11-08-2012, 12:49 PM   #7
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Well, there you go.

Post pictures.
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