The Stovebolt Site Forums The Shop Area The Electrical Bay My A/C switch melted!

I have a 1955 Chevy with a 350 V8 and aftermarket A/C. It has worked fine for years. Last week went for a 20 mile drive, it was 98 degrees. I stopped in front of my house and all of a sudden the A/C fan stopped and I could smell burning. I of course immediately turned of the truck. I took the A/C switch out and the resister, and wire clip was brown and melted. Not sure if this was an issue that has been building up to failure or if it happened all at once. I also noticed that the hot wire from the alternator was burnt and melted. The truck starts fine so I assume the ground wire is fine. (I have a strap from the starter bellhousing bolt to the frame and another to the cab.

What would be your recommended steps to test out where the issue may lie? In the meantime, I bought a new A/C resistor switch but don't want to install it until I get an idea of the issue. Also, does anyone know where to buy a new wiring clip for the Indak 3,223,794 switch? Photos below.

https://freeimage.host/i/djQK1s
https://freeimage.host/i/djQ2LX
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https://freeimage.host/i/djQB2f

Thanks for any advice!

Not knowing where any wires go can't really help with trouble shooting, but is the system fused properly? Seems like a fuse should have been taken out before things got that bad. I would think the compressor clutch coil would be the item with the highest amp draw in the system. I would trace damaged wires to make sure nothing is chafed and grounding some where.

Offhand it sounds like your A/C fan shorted out in the process of dying and this has fed that short back through the alternator somehow...the "somehow" part being "who wired this without a fuse for the fan motor and what sort of wiring scheme was used in the first place?" There should have been a fuse for the fan motor, the compressor, the fan blowing air through the evaporator/radiator...everything.

I would think the manufacturer of your a/c could provide needed parts if you can’t find them at your FLAPS. I agree with above comments. Time to get your VOM and fuse/fuse holders out.

Check the current draw of the fan motor. It pulls considerably more amperage than the clutch coil and worn bushings in the motor can cause the armature to drag and prevent the fan from coming up to normal speed. A slightly stalled-down electric motor will pull huge amounts of current because the windings don't develop the "counter EMF" required to limit its current draw. That's the same reason that continuing to run a starter after the battery gets a little low can destroy both the starter windings and the battery.
Jerry

I had wired the truck according to the universal wiring kit that I installed. It has worked great for years. So I always ask myself, what changed?
A year ago, my electric fan just started running all the time, it used to only start up when the temp hit a set degree. About 6 months ago I installed a fan on/off toggle switch. Normally whenever the A/C is on, it automatically turns on the fan. I may have had the toggle off and the A/C was trying to turn the fan on. Could that cause a problem like this?

Is there a relay for the a/c fan or is full power going through that switch?

If no relay, it may just be a matter of wear and tear due to a slightly undersized switch and harness.

I'm sure that motor pulls a little juice.

The General Motors HVAC systems from the 70's through the 90's or so only used a relay for full blower speed. The lower speeds went through the fan switch contacts and a stack of nichrome resistors that hung down into the air stream from the blower to keep the resistance wires cool.
Jerry

I always use the blower at full speed cause it is flippin hot in Texas. I will see if there is a relay and remove that toggle. I should go ahead and fix the fan control box so it only starts the fan when the correct degree is hit. That may be the problem right there! Why is electrical stuff such a pain?! LOL!