Troubleshooting for my husband. AC keeps blowing fuses

  • 1986 NISSAN 300ZX
  • 2WD
  • 100,000 MILES
My husband has a Nissan 300z and when you turn on the scene, it pumps nice cold air for a few minutes, then, the fuse blows and no ac. I want to prove to him that this site works and possibly get the name of a reliable, known z mechanic in our area.

I like this website idea and will donate, but first, I need to prove to him that great stuff like this exists.

Thank you very much for your advice.

Do you
have the same problem?
Wednesday, August 27th, 2014 AT 3:40 PM

1 Reply

We're all over the world so we don't know individual mechanics or shops. Every town has at least one mechanic who is very good with electrical problems, and all larger cities have shops that specialize in that. I have two former students working for my town's premier automotive electrical shop. That owner never advertises because he is so swamped with work.

If you want to tackle this yourself, 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 12 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.

That's my generic reply but I need to qualify it for your situation. There's three of four fuses in the AC system. The brake light bulb will work fine if the blowing fuse is a small one like a five or ten amp fuse. If it's a 20 amp, such as for the AC compressor, that circuit draws so much current normally that my test bulb is going to be real bright even when the problem is not present. To be more accurate you would need to substitute a head light bulb. It will work the same way but it will allow more current to pass.

Also, you must understand that with a bulb in the circuit in place of some fuses, the circuit isn't going to work. In the case of the compressor, it won't turn on and run, but the test bulb will be dim until the short occurs, then it will get full brightness. If it helps, think of trying to spin a fan with the stream of water from a garden hose. Adding a test light in place of a fuse is like standing on the garden hose and partially kinking it.

A different approach is to disconnect something, then see if the fuse still blows. The problem here is you need a steady supply of fuses. The best suspect is the compressor clutch. That can be disconnected, and the rest of the system will work normally. You just won't get any cold air.
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Wednesday, August 27th, 2014 AT 10:28 PM

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