Temperature Guage

[sgr60]

My temperature gauge isn't working, so I went to the engine compartment to check and see if I could find where the sensor is.

I was a little confused by what I found.

In the photo below you can see a black wire going into a bolt on the manifold, I would think that this is the temp sensor, but it's connected to a black wire that leads to the AC compressor, as opposed to back to the firewall.

Maybe this is related, there is a green wire going back to the firewall, but it's connected to something I can't idenitfy - I've circled that in blue. It's bolted to the carb, but doesn't look like it's connected to anything. Any idea on what this is?

Thanks.

[hatzie]

That's an AC idle solenoid. The 1984 wiring diagrams don't show it but they may be wrong.

Make sure the AC controls are set to OFF then Ground the Green wire. If it's the temp wire and everything else is OK it should nail the temp gauge at the top with the ignition on.

Informational note: 0Ω is High and 3.4KΩ is Low.

[sgr60]

Originally Posted by hatzie

That's an AC idle solenoid. The 1984 wiring diagrams don't show it but they may be wrong.

Make sure the AC controls are set to OFF then Ground the Green wire. If it's the temp wire and everything else is OK it should nail the temp gauge at the top with the ignition on.

Informational note: 0Ω is High and 3.4KΩ is Low.

Sorry, pardon my ignorance on this - if the green wire is for the AC, why would grounding it peg the temp gauge? The green wire from the solenoid goes back to the firewall. The black wire from the bolt in the head goes to the AC compressor - which is not operational at the moment - no belt on it.

Thanks.

[Just call me Sean]

It's just to test to see if you have the right wire, which it appears you don't. That's a/c stuff, it's green as is the temperature sensor wire. Temperature sensor is drivers side head, between the exhaust ports.

[hatzie]

I was questioning whether the idle solenoid was actually a 1984 AC system part... It doesn't show up in the wiring diagrams.
Both Temp Sender and AC Idle Solenoid are typically Dark Green wires. Real easy to mix up. Just eliminating it as a potential screwup by a previous owner when they installed the targetmaster.

See the 1984 GMC wiring manual in the RTFM below. It'll show you the bulkhead connector position for the TEMP wire so you can just buzz it with a meter if that makes you more comfortable.

[sgr60]

Ok, thanks - I'll give it a shot tomorrow and see what happens.

[Just call me Sean]

I would have to assume that it is a factory part. Every carbureted a/c equipped vehicle I've ever seen had an idle up solenoid.

[sgr60]

Originally Posted by Just call me Sean

I would have to assume that it is a factory part. Every carbureted a/c equipped vehicle I've ever seen had an idle up solenoid.

So that unit causes the throttle to idle up when the AC runs?

What about the two wires coming off the plug on the AC compressor - why does one run to the bung on the manifold just below the blue circle in the photo? What's that for? That's what I assumed was the temp sensor for the gauge, thought it was strange it went to the AC...

[Just call me Sean]

Yes it idles up the engine so the drag of the compressor doesn't make it stall.

That's ground for the compressor. The other is power for the compressor, and power to the solenoid. If the wire to the solenoid doesn't connect to the wire on the compressor then it's possible someone put the temperature wire on the solenoid. Since you say it runs directly to the firewall then I think it may be the temperature wire. Turn the key on, a/c on and test it for power. If it has power it's the solenoid power, if it doesn't then ground it and see if the temperature gauge goes up.

[sgr60]

Originally Posted by Just call me Sean

Yes it idles up the engine so the drag of the compressor doesn't make it stall.

That's ground for the compressor. The other is power for the compressor, and power to the solenoid. If the wire to the solenoid doesn't connect to the wire on the compressor then it's possible someone put the temperature wire on the solenoid. Since you say it runs directly to the firewall then I think it may be the temperature wire. Turn the key on, a/c on and test it for power. If it has power it's the solenoid power, if it doesn't then ground it and see if the temperature gauge goes up.

So the green wire coming from the AC compressor should be going to the solenoid? That's definitely not how it's hooked up, I can't remember now where that wire from the compressor goes (definitely not to the solenoid, but can't remember where).

I'll give your diagnostics a try - but I don't have a belt on the AC compressor - wasn't connected when I bought the truck - so I'm not sure I'll be able to test as it is. IF it turns out that the green wire going to the solenoid is in fact the temp gauge wire, where should that connect to ? I thought I found the temp sensor itself in that photo, but it seems like I didn't...

For what it's worth, I found this wiring diagram, but it doesnt include the AC, so it's not that helpful...

[Just call me Sean]

A/C doesn't have to work, it will still get power as long as the fuse isn't blown. If the compressor locked up you would have to unplug it, remove the belt, or both. Sound like they removed the belt. The green wire would go to both the compressor and the solenoid.

[sgr60]

Found the AC wiring - it looks like based on this that the AC might be wired properly and I need to continue my search for the culprit in the non-working temp gauge...

[Just call me Sean]

1. A/C wiring. It's newer so ECM is idle up solenoid but otherwise the same.
2. Your oil pressure switch from the other thread, on the left.

[Just call me Sean]

My diagram pics kinda suck. Temperature gauge sender, brand new and not plugged in.

[sgr60]

Awesome - thanks for the photo.

[hatzie]

Originally Posted by sgr60

Found the AC wiring - it looks like based on this that the AC might be wired properly and I need to continue my search for the culprit in the non-working temp gauge...

I missed that in the RPO C60 pane of the diagrams.

The solenoid wire should be Light Green.
The solenoid wire in your pic looks like it's Dark Green... If it goes back to the firewall block and not to the 2 position Packard 56 AC disconnect then it's probably your temp sender wire.