[kingnutin]

The other day my fan control quit working, fuses are okay, didn't mess with anything... I'm confused, I will try tearing into the dash if nobody has any other ideas.

 

[COLD STEEL]

Check the blower motor for power going to it. Common for the motor to quit.

 

[77Impala]

Check the motor ground wire, have seen it break or corrosion to cause problems.

If you do not have 12 volts to the fan motor then try this. To find if the ground is the problem hook your test meter ground lead to the body of the car and check the hot wire for power, if power is sufficient then fix the ground wire.

 

[dintymoore]

Last year that happened on my '92 and it was the blower resistor, which is on the blower case (the case the blower motor is in), very close to the blower motor. It's under the dash on the passenger side. The damage was visible when I took it out - bad corrosion.

 

[kingnutin]

Ground lead has about 110 ohms resistance to the battery, not enough to cause trouble. No power to the motor...

 

[kingnutin]

About the resistor though, I don't know which leads to test or what resistance to look for. Luckily it is not under the dash on a 78, its right next to the motor in the engine compartment.

 

[dintymoore]

You can test the resistor with a meter. If you get a reading of infinite, that means there's a break in the resistor, and that will result in the fan getting no juice. So look for "some sort of resistance reading" or infinite. Infinite = broken.

All the resistor does is insert resistances between the battery and the motor to give you different fan speeds. When the fan switch is on high speed there is no resistance inserted in that path. You can duplicate high speed by using a paper clip in place of the resistor.

Also, the switch for the fan motor could be bad, but this is rare compared to the resistor "wearing" out from cycling hot and cold, which brings on the corrosion. The resistors are made with regular steel wire instead of stainless, that's why they fail.
You could run a wire right from the battery to the fan to make sure the fan motor works and it's not the switch.

 

[kingnutin]

Just to be clear, how many wires should I see going to the resistor so I know I'm looking at the right part? That figure would be more helpful, but it is for the later models.

 

[dintymoore]

I think the resistor has got a three wire connector with orange, light blue and yellow wires. The resistor is mounted very close the blower motor.
If you backprobe the different wires on that connector you might be able to see if juice is getting that far.
On my 1992, as soon as I removed the resistor the damage was visible.

 

[kingnutin]

Okay, mine has 5-poles. I need to check for voltage later, but when I disconnected it and checked for continuity, I could only get it between two of the poles. So I suppose I should try it plugged in with the power off, and check which wires go to the poles I got continuity on.

 

[dintymoore]

I'd try pulling it to see if the damage is visible.

 

[Guest]

If it was the blower resistor the fan should still work on high as the high speed relay bypasses the blower resistor. It's either a bad ground for the motor or a bad motor.

 

[dintymoore]

When my resistor broke last year it did not work on high or any other speed. When I opened it you could see that one of the spring type resistors was broken.

 

[kingnutin]

And since I am not getting power to the motor, the ground isn't the issue. I'll have to see what the resistor costs.

 

[dintymoore]

I was able to get mine to working (and at custom speeds!) by removing it, seeing the broken corroded spring resistor, and twisting the broken parts together... used it like that for months.