Blows fuse when turning on A/C

Have you tried removing the fuse and hooking a a bulb test light across where the fuse goes?Then the test light should glow bright if there is a dead short on the circuit. You can unplug the compressor move wires around and watch the light on the test light. It will help you find the blown fuse.

If you suspect the compressor clutch, just unplug it. You do not have to replace it as a test.

A simple trick to finding a short is to replace the blown fuse with a pair of spade terminals, then use small jumper wires to connect them to a twelve volt light bulb. A brake light bulb works well. When the circuit is live and the short is present, the bulb will be full brightness and hot so be sure it's not laying on the carpet or against a plastic door panel. Now you can unplug electrical connectors and move things around to see what makes the short go away. When it does, the bulb will get dim or go out.

The 10-amp "gauge" fuse feeds a computer module in the passenger junction box behind the right side of the dash. Unfortunately the way the wiring diagrams are drawn, there is no way to follow the current path for the AC switch or the module. There is also an "AC amplifier module" behind the center of the dash that you might consider.

The problem is if you unplug a module, then the test light is dim or the fuse does not blow, is it because that module is shorted or because something further down the line is shorted, and current cannot get to that short because it has to go through the module you unplugged? I never approve of throwing random parts at a problem in hopes one will solve it, but in this case, I cannot tell you a logical set of steps to take to find the cause, and this might be one time you will have to just pop in replacements to try. I would find some used modules at a salvage yard, assuming you have not found a bare wire or other cause up to this point.

If you tried what myself and cardiodoc suggested with the light that will really help. It has to be something with the A/C compressor turning on. Wires clutch etc blowing fuses is not easy to diagnosis. Power probe brand tools makes a circuit tracker that will tell you where a dead short is with a circuit tracer you follow the wires with.

Also, you're forgetting the easiest step. Just unplug stuff.

We're looking at different fuses. On my diagram, it only feeds a couple of circuits.

Don't replace parts. Unplug them. If a module is shorted internally, unplugging it removes the short from the circuit. Even then there could be something shorted that is fed THROUGH the module you unplugged, so there's more things to check before you order a part.

Actually, you made a huge leap of progress, but the way the diagram is drawn, it shows representations of assemblies but not the wires that I can follow. I have found some suspects though.

The best one is a diode block that is supposed to dampen voltage spikes. Diodes are one-way valves for electrical current flow, but diodes often fail by shorting. Look for this assembly behind the right side of the dash, possibly near the fan motor. It has three wires; a black, a light green / black, and a red / yellow or a white wire. Unplug that, then see if the short is still there.

By "AC modulator", could you mean the "AC accumulator"? It's not possible to figure out which circuit feeds that and could have the short on it, but if you unplug the amplifier and the short is gone, we're past the point of confusion anyway. The compressor clutch is one line, but you unplugged that already and it didn't help. Next, another circuit feeds the "Air inlet control servo motor", behind the right side of the dash. That is probably mounted on the heater box assembly. If you can figure out where that is, unplug it. Its wires are, ... Uhm, ... White, white, and white. All three of those wires come right from the AC control switch. If you have another control switch, try that too. It has a number of circuits that get 12 volts fed to them when it's turned on.

Before I get dizzy trying to follow the other wires, check the items I listed so far and see if any of them remove the short when you unplug them.

Another suggestion you unplugged the a.C. Compressor and the short was still there I had a car like that. Turned out the wire going to a.C. Compressor in the engine compartment was shorted to ground.

Saturntech9's comment reminded me that some vehicles use a spike-suppression diode in the wiring harness near the compressor clutch's plug. If that diode was shorted, that short would be on that line but unplugging the compressor wouldn't change anything.

I don't know how this system works, so I don't know which other wires get 12 volts from the "Gauges" fuse. I'm starting from the amplifier instead, but it could be the amplifier itself is shorted. It has a ground wire, a 12 volt feed wire, and some circuitry in between. That means it's a candidate for creating a short between the feed and ground wires.

What I'm thinking this might come down to is checking each amplifier wire individually to see if we can find one with a short, but that's easier to do than to describe.

I'll be back tomorrow to read that you solved the problem!

Unplug the AC amplifier, then find terminal # 6 in the plug. That's listed as a "black (or white) wire. Measure the resistance of that wire to ground. Tell me what you find.

Do that test again with the AC compressor unplugged and tell me what you find.

You may be down to substituting parts. The problem is the short could be on a circuit that is turned on by a module. That means the short won't cause the fuse to blow until that module switches on. That's where I was with the black wire. Perhaps Saturntech9 has some better ideas.

A fan motor can easily draw more than ten amps so they are commonly protected with 20 or 30-amp fuses. I would expect a ten-amp fuse to protect the circuit that runs a relay for the fan. Relays draw very little current.

Regardless, I'd unplug the fan motor and see if that solves the problem.