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87 Caballero Amarillo, stock 305/200R4/QJ
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Discussion Starter · #1 ·
So in typical Chevy fashion, half the stuff electrical works backwards. So as is, I have no power to the Idle Stop Solenoid, whether ac is on or not. Chased that down to the ISS relay on the passenger fender, which is powered and engaged. Manually disengaging the relay makes the ISS kick, has 12v.

So my question is where does that get its power from or is switched from so that when I hit Max/Norm/Bi, the relay gets unpowered/disengages and allows the ISS to kick out as it should with 12v?
 

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87 Caballero Amarillo, stock 305/200R4/QJ
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544 Posts
Discussion Starter · #4 ·
I traced the pressure wire, it's good, get test light lit when that's on. Get ign when that's on, plunger activates with ign 'on' / ac off. Plunger deactivates with engine 'on' / ac 'on'. Only thing that doesn't seem to be good is ground circuit from ecm?
I'd toss the whole thing and go straight from the ac to the solenoid, but there's a speed thing, the ISS deactivates after about 40mph (whether ac is on or not) so if you hit the brakes the carb can drop to curb idle for tranny/brake vacuum needs.
 

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I have a 79. It never shuts off unless the compressor is off. No engine management system. With the a/c on it raises the idle 200 rpm 5-700 in gear on the tach.
Tom
 

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87 Caballero Amarillo, stock 305/200R4/QJ
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544 Posts
Discussion Starter · #6 ·
That's a thought. Mines an 87 and fully stock, so getting verry tempted to start snatching everything smog that I can and just dumping it in the trash. But being an 87, everything is tangled with everything else. Computer quadrajet, computer dizzy etc. Even the vac line going to the EFE on the exhaust is T'd and goes to some sort of relay mounted next to the idle stop relay. (not on any vac diagram I can find, so no idea what that is). It's a mess of good intentions and bad ideas. You'd think a low oil pressure would light a low oil pressure idiot light, oh no, low oil pressure lights the choke light instead.
 

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87 Caballero Amarillo, stock 305/200R4/QJ
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544 Posts
Discussion Starter · #7 ·
Ok, so I found the issue. It was the pressure switch, sort of. The switch was good, the line from the compressor was good, both showed 12v. What wasn't good was Chevy in their wisdom ran the wire through the same 4 prong connector as the fan speed wiring after the evap switch and that had a bad connection. Little crimpage and it's all good again. Had no idea that was done that way, why run a wire directly from the compressor to switch on opposite side of the motor, then break it before the relay that's not 2 feet away. Strangeness.
 
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