gearheads78

The a/c blower keeps popping the fuse a few seconds after turning it on in the 98 so I started digging, What I found is a burned up connector at the switch and wires close to it melted. Nothing is shorted to ground and can't find any wires melted together. I had an A/C harness from a 78 truck I parted out so I have now fixed the connector and wiring but I still have to get a new switch. Any idea what could have caused this and what to watch for so it does not happen again?

98olds001.jpg?t=1335154021

Now that we have that out of the way when does the thermal switch on the back of the heater valve come in to play? When I was searching for a wire issue I found the thermal switch broken off and hanging against the firewall.

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MDchanic

Hi Richard,

You need to determine exactly which wire it was that overheated, if you can, then you can check to see why. All of the wires except for the orange and black one go through the resistor block before going to the motor, and the orange and black one goes to the relay instead of the motor, so none of them should be carrying full current to the motor itself. If there is a short in the resistor block, it could lead to too much current flowing through one of the wires. Another possibility is that the motor bearings could be tight and drawing too much current when it runs - the only speed where there is a chance of this melting a wire is the second-highest speed (light green wire, I believe).
The brown wire is the feed - if it is the burned one, then there could be / have been a short in the switch or elsewhere in the controller.

Of course, sometimes the darn things just overheat...

As for the thermal switch, it disables the Low speed at coolant temperatures below 40°F.
You can either leave it as-is, in which case the Low is actually Off, or ground it, in which case Low will be Low.

- Eric

Lady72nRob71

Check operation and current draw of the blower motor. I suspect it is on its way out.
Pull the blower resistor and clean up the terminals that that burned plug attaches to if you havent already.

gearheads78

Rob whats the best way to test the current draw on the blower? I looked at the connector for the resistor and wires to it they look OK. The wire that caused the conector to burn up is was the brown wire to the selector and blower switch. I replaced about 10" of that wire well back of any signs of damage.

joe_padavano

The problem is that you had a dirty or loose terminal that overheated due to added resistance. I have this happen all the time on my 84 - there's a similar four terminal connector in the engine compartment that supplies power to the blower motor. The Packard 56 terminals are not the greatest and they are certainly not weathertight. That's why GM changed to the Weatherpak series.

Lady72nRob71

With an ammeter that reads up to 50A or so. I used a cheapo one from harbor freight.

Here is how I did mine last year...

Using the original battery and an inline ammeter, it worked, and strongly it did! It about twisted itself out of my hand on startup, peaking almost 50 amps before it came up to high speed and settled down to a constant 10-12 amps.
There is a movie file below of this test below.
https://classicoldsmobile.com/forums/...1&d=1314500487
I used the camera to get the best view of the ammeter. Luckily, when installed in the car, the blower is already turning when high speed is selected, so the initial startup peak would be lower.

After cleaning and polishing the contacts, use some dielectric grease on them to prevent corrosion and resulting resistance, arcing, and burning.

gearheads78

Whats your favorite method of cleaning the contacts?

MDchanic

I like a cordless Dremel tool with a tiny wire brush - makes 'em shine!

- Eric

joe_padavano

I physically remove the terminals from the housing, wire brush or file, and rebend the contact surface before reinserting. One of these really helps:

Lady72nRob71

Correct! Looks like you were a graduate of.........

Rob's Skule of Terminal Repair!
https://classicoldsmobile.com/forums/...tml#post312739

MDchanic

I bin ejumucated right good.