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Discussion Starter · #1 ·
My little donor car had an issue with its fan speed control from when I bought it... it has ONLY full-on fan speed, the fan does not come on at all at lower fan speed settings. The fan speed selector is a mechanical slide with about 4 distinct 'click' positions....

what should I be looking for in terms of testing to see if I can repair, or need to replace? I have not really pryed apart the dash, and am hoping to avoid that, but might have to get to the back of the slide....

I would like lower speed, in part because I think it would allow my 1500watt heater to keep up and produce hotter air, with less noise.
 

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The heater control will pull out from the dash if you undo the cables from the heater and outside air vent, remove the knobs on the controls, and the cover on the "console". The cover pops off the top of the switch to reveal the copper switch parts inside. It is a really cheap switch. The spring, which is what supplies the "click" into each position, had bent on mine so it just kind of slid around freely. I straightened it out and its worked since. I suspect the little "bump" on the movable part is not contacting the bottom copper segments of the switch for your lower settings. Could be the cover has just popped up on one side - it hardly holds together. You might drop the glove box down all the way open (press the sides in so the catches slip out) and try to reach your hand around to feel if the top of the switch feel like one side is popped up. Yeah, not a lot of room in there to work. You can have one of three: light where you need it, your hands where you need them, or line of sight where you need it.
 

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Discussion Starter · #3 ·
thx Tom, you are inspiring me to attempt a look... I suspect that the board cracked, or perhaps wires from 'positions' are damaged. The radio was stolen, and the hacks just yanked the sucker out, so it might be as simple as wires pulled off... I just dunno how har it might be to get in there without MAJOR dash disassembly.
 

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Fan speed on most cars is controlled by a large wire wound resistor with multiple taps. This resistor is usually located somewhere in the heaters air stream to cool it.

The basic function is simple. The resistor serves to cut the voltage the motor sees to create the lower speeds. One end of the resistor is connected to the motor to power it. When the heater switch is off no power goes to the resistor so no power goes to the motor. Low puts power to the resistor at the end opposite the side connected to the motor (maximum resistance.) Speed 2 connects to a tap part way up the resistor, and speed 3 one even closer to the end connected to the motor. High fan speed connects power to the motor directly without using the resistor, sometimes to the resistor at the same terminal as the power wire to the motor in other cars the motor directly.

When heater fan high is the only speed that works usually you will find the wire wound resistor burned out somewhere between the end connected to the motor the tap closest to it. You can often get the fan working with 3 speeds by jumping the last tap to the end of the resistor, though it may cause the resistor to run hotter (shortening the life of the rest of it.) Then you would have speeds low, medium, high, high (with the jumper the 2 speeds on either side of it would be the same.)
 

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The power resistors that control your speed is a common problem with age, check it first.

Also since you still use the same amount of electicity in low and medium speeds, get a PWM board off ebay and put a pot on your dash, and you will have full variable speed. If you insist on using the original control, use it with speed set resistors to the PWM board.

Roy
 
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