a/c problems

[Jay2TheRescue]

Well, I've been having problems with Big Red, our 2000 GMC Savana 3500 1 ton van. Last week the a/c fuse started blowing after about 10 minutes of operation. Since then I've replaced the resistor, dash switch, and blower motor. I'm still having the fuse blowing after about 10 minutes. The only thing I can think of that hasn't been replaced is the high speed fan relay, but at this point I'm going to be really pissed if I fork out more cash, and I still have problems.

What's the likelihood that a bad relay might be causing this problem, and if anyone has had a similar problem, what turned out to be the source of the problem? With how hot its been, I really need this a/c to work.

[theholycow]

Can you test current usage at each part to see which one is pulling all the current?

[Dr. Jerryrigger]

It could be a short somewhere in the system. I'd attack it with a DMM before replacing anything. If you have a schematic of the system you can see what is really on that fuse and test to see if any of those things have low resistance, or pull high current. It's a PITA job on anything newer than 1989, but it's better than tossing parts at it.

Also if it is happening at just about 10min every time, then it may be something that is warming up and then shorting out. So testing it just after it blows a fuse may be necessary.

[Jay2TheRescue]

Yeah, I think something is getting hot, but being a van, getting to stuff under the dash is not easy. The fuse blows at about 10 minutes, and if the fuse is immediately replaced it will blow again within one minute.

[Dr. Jerryrigger]

do you know everything that is on that fuse?

If you can isolate different parts you could load them directly from the bat (with it's own fuse), and see what happens after 10min.

[Jay2TheRescue]

AFAIK the only thing on the fuse is the blower motor. When the fuse blows the compressor clutch stays engaged. If you're traveling at highway speeds you can ram a decent amount of air through the system, problem is I rarely drive it on the highway.

[Jay2TheRescue]

Well, did more work today. I tested the resistance of the ground for the motor, and didn't like what I saw. I replaced the ground, and the fuse still blew...

[Dr. Jerryrigger]

So is the fuse blowing if you run just the fan w/out A/C?

[Jay2TheRescue]

I'll have to try that, but I suspect it would. The blower motor seems to be the only thing on the circuit.

[Jay2TheRescue]

Ok, I just stopped by the house and picked up the van as the heat of the day has subsided. I drove it back to work, about 10-15 mins in rush hour traffic with the vent on high, and the fuse didn't blow. I guess I need to re-visit the a/c clutch. I thought the compressor was still running when the fuse blew, but maybe I was wrong.