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Old 07-17-2008, 05:46 PM   #1
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Amp Cooling Fan Question

Ok, so I've got an after market amp in the front trunk and it got too hot today and shut down. I have a 12 volt DC cooling fan from Radio Shack and it has a red and blue wire. I hooked up the red wire to the amp power supply, which goes to the battery and the hooked up the blue wire to the amp switch wire from the radio.

Follow me so far?

When I connect the wires with the car off the amp turns on but the fan doesn't, which is ok except the amp shouldn't switch on.

If I connect the red wire to the batter and the blue wire to the ground the fan goes on, which makes sense to me

My question is why would connecting the cooling fan blue wire to the switch wire from the radio turn on the amp? It also makes a loud pop when I remove the switch wire.

What's the correct way to wire a cooling fan so it goes on when the radio / amp is on and off when the car is turned off?

Any help is appreciated.

Thanks,
-Steve

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Old 07-18-2008, 12:44 PM   #2
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Your amp has a 12v (hot) wire that is switched and a ground wire or chassis ground.
Connect your fan the same way: 12v (hot) switched, chassis ground. Then they will come on and off together.

If your amp is overheating it may be that your speaker load is too low impedance for the amp design causing over current and shutdown. Disconnect the speaker wires from the back of the amp and test each speaker wire with an ohm meter. If any are below the minimum ohms rating for the amp you have a problem. Most modern amps can run 4 ohms all day. Many amps can run as low as 2 ohms.
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Last edited by Topless; 07-18-2008 at 01:01 PM.
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Old 07-18-2008, 06:08 PM   #3
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I'm 99% sure that the amp over heated because it's damn hot in the front trunk - I was cranking the amp for 1/2 hour+.

I read somewhere that I need to connect the blue switch wire from the radio to a relay then to the amp and fan switched connections...

I'll try again but I did try the following:

This is causing the issue, the fan is turning on the amp when it shouldn't
Amp always hot wire -> Fan hot wire
Amp switched wire / lead -> Fan negative

Fan always on:
Amp always hot wire -> Fan hot wire
Amp negative -> Fan negative

I'll try
Amp switch wire / lead -> Fan hot wire
Amp negative ->Fan negative
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Old 07-18-2008, 06:53 PM   #4
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I feel sheepish - that did the job! I connected the cooling fan hot wire to the amp switch wire and the fan negative to the amp ground terminal and it works! That was the only thing I didn't try... Thanks!

I didn't realize that the switch wire is a full 12 V when on!

Now my pop sound is back! When I turn off the car it pops. When my amp switch wire is disconnected - which disconnects the amp - there is no pop sound so clearly its coming from the switch wire that I'm running from the head unit harness to the amp switch input...

Any insight is appreciated!

-Steve (a novice stereo guy)
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Old 07-19-2008, 11:36 AM   #5
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One more on this topic -

I did find that if I turned off the head unit before removing the keys from the ignition I don't get a pop from the amp

If I leave the head unit on and pull the keys out I get the pop. I think the switched lead from the head unit is doing something goofy to the amp...

Any insight on this topic is appreciated.

-Steve
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Old 07-21-2008, 06:28 AM   #6
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That POP is a common problem even in professional audio. Many amps have a power up delay or ramp up to avoid this. If yours does not simply turn down the volume on your head unit before power up/power down so you don't amplifiy the POP.

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