HVAC switch blows fuse but only in some settings

[Curious Hound]

Good job and congratulations.

It sounds like the coil in the relay has failed. After time, the insulation in coils, motor windings and other electrical devices deteriorates and eventually allows the electricity to leak and jump across wires in the coil. This bypasses the rest of the coil of wire and the resistance it contains, thereby creating a low resistance, or "short" circuit which allows excessive current to flow.

The deterioration of Insulation is accelerated by heat, dirt and chemical exposure. So, the engine bay of a vehicle is a bad place for electrical stuff.

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[marknreimer]

Well unfortunetly it looks like my fuse issue has come back. I had no issues for a couple days but yesterday it popped again as soon as I went to set the vent to the first position to the right of OFF, which is dash vent and floor boards.

Last time when I pulled the blower relay, I wouldn't pop a fuse. So I tried that again, but this time the fuse DID pop.

I had also had success by unplugging the AC compressor clutch, so I did that, fuse popped again.

So I unplugged the ac clutch, took out the relay, and unplugged the pigtail at the back of the compressor too. Nothing blew at this point, so I started putting the stuff back together. Then my blower worked again!???

So I left the engine running and wiggled all the connections, shook the wiring harness, tapped on the fuse box, relay, dash controls, everything I could think of to make a short rear its head. Nothing happened, it just kept working.

I came back an hour later and went on a drive. A few minutes in I switch on the floor board vents and POP.

What is going on?? I've tried to isolate the blower circuit, the AC compressor and clutch circut, the relay, sometimes a test comes back as bad, then the next time as good, and so on.

Since I've blown a fuse now with the ac compressor disconnected, and I've also blown a fuse with the blower relay disconnected, does that narrow it down to the dash switch, or some bad wiring between the switch and the vent doors?



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[telsar]

Defrost setting turns on the AC compressor.

 

[marknreimer]

Defrost setting turns on the AC compressor.

Yeah, but I'm blowing it in the floorboard position, which comes before defrost on the dial.

I disconnected my AC pressure switch by the blower since it's tied to the same fuse. Haven't blown it after two short rides. Gonna keep driving for the day and see if it keeps up. Might have a fault in that bit of wiring


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[marknreimer]

Well it's been a few days now and about a dozen trips without blowing the fuse. So it's safe to say that it's a short in the harness related to the pressure switch on the back of the AC compressor. Time to find the multimeter


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