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Old 09-13-2006, 10:29 PM   #1
kna4977
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1972 Chevy Truck A/C Fuse Box Wiring?

I just installed factory A/C in a non-factory A/C truck supplementing the original harness with the A/C harness. Everything still works as it should except for the heater fan. I've replaced the control switch and the relay. If the switch is placed at the High setting, the fan blows Low. If it's placed at Off, Low, or Med, the fan blows on High. The new harness has an anti-dieseling harness connector built in, but there is not a relay as the original system didn't have this component.

At this point, I'm not sure what I have done wrong. I do however need a picture of the fuse box in an A/C truck with everything wired correctly, so that I can at least get back to a starting point to try and solve this problem. I cannot find a diagram that is understandable that combines the regular harness and the A/C harness together. In fact all I can find is just the A/C diagram.

Another thing about the A/C diagram is that it wants you to wire the Orange wire into the cig lighter outlet, but if I do that, the fan blows all the time on high as long as the battery is connected, so I have no choice but to wire it to another accessory that turns on with the ignition. Any help or suggestions would be greatly appreciated!
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Old 09-14-2006, 03:27 AM   #2
Aarons72s
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Re: 1972 Chevy Truck A/C Fuse Box Wiring?

Man that is strange. I always have problems with the rellays going bad. Plugging in the orange wire into the cigarete plug and it blows constantley? sounds like the relay is stuck closed. But other than that I don't have to much else to think of. So here is you a bump. Good Luck

Last edited by Aarons72s; 09-14-2006 at 03:27 AM.
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Old 09-14-2006, 10:35 AM   #3
sneakysnake
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Re: 1972 Chevy Truck A/C Fuse Box Wiring?

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Old 09-16-2006, 09:52 PM   #4
kna4977
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Re: 1972 Chevy Truck A/C Fuse Box Wiring?

I checked the control switch, resistor, and relay voltages with the ignition on then off, and the control switch moved through each position (off, low, medium and high)

Keep in mind that the fan blows on high through all control positions with the ignition turned off. When the ignition is turned on, it blows on high through all positions except when the control switch is turned to high. This is when the relay clicks and the fan cuts off.

The CONTROL SWITCH has a brown wire, an orange wire, a yellow wire and a light blue wire. With the ignition off, all wires to the control have 0v except when the control is at high fan. This is when the fan cuts off and all wires have a voltage of 11-12v. With the ignition on and the control in off position the only wire that has voltage is the brown wire. At low and medium the brown, yellow and light blue have voltage, but the orange doesn't. With the ignition on and fan switch on high all have 11-12v and fan cuts off


The RESISTOR has yellow, dark blue and light blue wires. With the control turned to off position all wires have 0v whether the ignition is on or off. With the ignition on, all wires have equal voltage (10v in low and medium, 12 v on high). With the ignition off, no wires have voltage until the control is switched to high in which they all have 12 volts.

The RELAY has a single orange wire, a double orange wire, a dark blue wire and a purple wire. With the fan on high whether the ignition is on or off all wires have 12 volts except the purple one of course. With the control at low or medium and the ignition on, all wires except the single orange wire have 10 v. With the ignition off, the double orange wire and the purple wire have 10 v and the dark blue has 0v. With the fan in off position, the double orange wire and the purple wire have 10 volts each regardless of the ignition position.

I know this is confusing. Please let me know if you have questions, and please provide me with all the help you can. This is becoming frustrating, and I know it has to be something simple.

thanks
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