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Old 06-09-2021, 02:14 PM
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79firebird_99TA 79firebird_99TA is offline
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Default `79 Firebird popping fuse #6

There is a short and I've isolated it down to something on the circuit that powers the AC compressor. Without the blower motor running, when I select AC or defrost, #6 fuse output goes to ground. Does some one have a schematic. I also wonder if there is something physical going on behind the climate control panel. Any ideas or schematics would be greatly appreciated.

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79 Firebird/`70 400 with `77 6x-4s shaved .065"/4 speed BW ST-10/Cliff Q-Jet/XE268/3.08
99 Trans Am/LS1/Vigilante 2500/Strano springs and Billsteins -1.25" drop
75 Corvette/L48 350 (LSx -4L60E one day)
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  #2  
Old 06-09-2021, 03:00 PM
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79firebird_99TA 79firebird_99TA is offline
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I pulled out the climate control selector and when I disconnected the connector seen in the picture, the short stops .... so if someone can tell me where that goes ... it is a single yellow wire that connects to a brown wire. Getting closer .....
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79 Firebird/`70 400 with `77 6x-4s shaved .065"/4 speed BW ST-10/Cliff Q-Jet/XE268/3.08
99 Trans Am/LS1/Vigilante 2500/Strano springs and Billsteins -1.25" drop
75 Corvette/L48 350 (LSx -4L60E one day)
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Last edited by 79firebird_99TA; 06-09-2021 at 03:01 PM. Reason: Perfectionism
  #3  
Old 06-09-2021, 06:41 PM
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Brown is the color of accessory feed. I suspect that's power for that A/C controls. Green is normal for what goes out under the hood.

I'd be looking under the hood at the A/C clutch plug, fast idle solenoid, etc..

Common burn and short areas are where the harness lays on the intake at the heat cross-over and near the EGR valve.

If any work has been done recently.. look around for a wire that might have gotten pinched between two parts.

Clay

  #4  
Old 06-10-2021, 09:21 AM
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79firebird_99TA 79firebird_99TA is offline
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Thanks for that info. The AC compressor's plug and the fast solenoid were the first places that I looked and those are fine. I think there is something going on behind the gauge cluster as I could break continuity to ground when I lightly shook some of the wires back there. I can't imagine what would come into play back there but it's the next place to look.

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79 Firebird/`70 400 with `77 6x-4s shaved .065"/4 speed BW ST-10/Cliff Q-Jet/XE268/3.08
99 Trans Am/LS1/Vigilante 2500/Strano springs and Billsteins -1.25" drop
75 Corvette/L48 350 (LSx -4L60E one day)
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Old Yesterday, 01:21 PM
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OK ... it appears to be the heater control assembly. I've verified that there is no wiring or load shorting to ground on those circuits. However, what I'm finding is that the green and the yellow (which goes to the fused side of #6 fuse) have continuity when I switch off of "off". That puts a ground on the load side of that fuse. So either the green shouldn't be ground and/or the switch on the heater control is faulty. If anyone has access to the schematic of the AC/Heater control circuit, I would appreciate it. I have a service manual in the mail, but it'll be a few days yet.
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79 Firebird/`70 400 with `77 6x-4s shaved .065"/4 speed BW ST-10/Cliff Q-Jet/XE268/3.08
99 Trans Am/LS1/Vigilante 2500/Strano springs and Billsteins -1.25" drop
75 Corvette/L48 350 (LSx -4L60E one day)
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Old Yesterday, 01:37 PM
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OK ... RESOLVED!! That green being grounded was the issue. That runs through the firewall and splits to the AC compressor as well as the idle up solenoid. There was a third green wire .... it ran to the ground on the firewall. DOH! That didn't belong there!
Anyhow, I've fully tested the circuit and it's good to go. Now ... it's back to where I started .... get the AC working. Heck, while I have things apart, I think I'll grab some dim-able LEDs for my gauges.

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79 Firebird/`70 400 with `77 6x-4s shaved .065"/4 speed BW ST-10/Cliff Q-Jet/XE268/3.08
99 Trans Am/LS1/Vigilante 2500/Strano springs and Billsteins -1.25" drop
75 Corvette/L48 350 (LSx -4L60E one day)
--------------------------------------------------------------
  #7  
Old Yesterday, 04:16 PM
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One thing to think about is most cars had the fan still running to keep moisture out of the box. It may be the fan circuit?

I may have some kind of schematic, but think it was hard to get one for a 79?

But if it's working OK, then good.


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