A/C relay troubleshooting

So here we are, heading back another (!!) 4K miles, from east to west this time around. Long story there... and even longer trip, haha! I'll post fun pics elsewhere... we're taking Route 66, and the van has had tons of waves already in its direction

Unfortunately, the A/C gave out right before the high humidity and temperatures climbed (we're right near Kansas currently, on the edge of Oklahoma, having just left Missouri). And we have yet to face the desert!

The issue with my A/C is that some prior owner did something wiring-wise that everyone since then (who has worked on the van) has cursed profusely. Right before our trip, I had the system checked out at Northeast Auto Imports. They recharged it, replaced some seals near the compressor, and also found that the A/C switch wasn't passing, I think it was sufficient power, in any case the compressor wasn't getting enough of a power signal to turn on, even though (again I'm trying to remember what Tyler said) the power at the compressor was as it should be, or something like that? That doesn't sound quite right, but it's something like that.

To resolve the issue, the tech added a relay switch. And the A/C worked great after that, for several days into our trip. Until it didn't.

I asked Tyler how I might troubleshoot this on the road. Here's what he said:

There's a fuse next to the battery you could check but otherwise if it's not that are you familiar with how a 4 pin iso relay works? that's hidden under the panel above the compressor on the left side of the engine bay. can follow the wire from the compressor. also may be worth just checking the wire at the compressor first to see if it is receiving power first.

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Now, I know nothing about 4 pin iso relay switches, but I sure would like to learn more about mine now. I'm afraid to confess that although I own a multimeter that came with the van, I do not know the first thing about how to use it (there's a dial to set)? I mean, I know I put the little prongs into places and then look at the meter, but I'm not sure where to put the prongs, nor what the dial should be set to for this purpose.

I took a few photos of the new things (sky blue plastic) that I could easily see were added. I can see the new relay switch mounted to the little board that my battery isolator sits on. I can't find the fuse Tyler mentioned. I *think* I hear the engine sound change when I engage the A/C right now, but I'm sort of not quite certain on that. Definitely no cold air, that's the only thing about which I'm certain now! Maybe the refrigerant all leaked out already too, I don't know for sure, but it'd be nice to test this relay switch somehow to rule out something electrical, knowing that my A/C has electrical issues as well.

This is the standard wiring for a four terminal (ISO) relay...

Here’s what I found: so if the ignition is on or the engine is on, the main red wire (that taps into the positive terminal of the battery) is carrying voltage between 12-14V, as expected.

Whether the ignition or the engine is on, none of the other wires is carrying any voltage at all, even when the A/C button is pressed in to turn the A/C on. This does not seem expected.

I can see that the red wire (at a right-angle to the other relay connections, labeled "To light/accessory etc." above) connects to a creamy female connector (old van wiring) that goes down towards the compressor.

I can also see that a black wire whose end is covered in electrical tape (compared to the sky-blue jackets on the other three wires) hooks into old van wiring, and that a brown male connector was taken out of the loop, with the wires spliced there under electrical tape. It also looks to head down to the compressor.

The other black wire goes to the battery ground, as expected.

That much we know, basically showing that the relay is not activating when the A/C switch is pressed.

It seems to me that if the relay is working, then the voltage should change from zero to 12-14V when the A/C button is pushed in, either on that red wire going into the old creamy connector down to the compressor, or on the black wire connected to the old van wiring with the brown connector that also seems to head in the direction of the compressor. Or maybe the voltage should change on both?

DeliKit said:

Or maybe the voltage should change on both?

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I believe it should change on both. I would guess your AC power switch has failed.

Try jumping battery power to terminal 86... if the AC turns on it's probably the AC switch. But it seems odd to me to bypass the original clutch relay with an aftermarket one if the problem was the switch.

I have a few NOS aftermarket replacement switches, but with the modified wiring I couldn't tell you how to put it back to stock.