Toyota Pick-up 1989 Blower Speed Control Unit

You'll find the answer to both those questions on my web page, in short

Wow, great! My blower on my 1984 Toyota ExtraCab pickup only works on the 2 fastest speeds and not the two slower speeds. I thought about add a couple of power resistors, but looks like I can replace the whole resistor package.

Thanks for the post! Nick

Rudy wrote:

Your instructions were flawless! Thank you very much. Actually just for fun, I am thinking to replace the resistor box with a PWM circuit (I am also a EE), but my only problem with the PWM is that I have a dog and therefore I have to go > 55KHz to avoid any acustic disturbance due to magnetostriction, to my dog's hearing. At half speed, the series resistor wastes ~50W! Rudy

Heck with the dog, there are some people here who can hear the flyback in the television set. And that's up in the 40KHz plus territory. ;-) I wonder if a simple variable voltage regulator circuit would do it?

If you can make an electronic speed control that works reliably, design it to plug in right where the resistor pack goes - with possibly a body ground wire for running the electronics. If you make it easy to retrofit without cutting or splicing any harness wires...

You might be able to make a few bucks as a side company and offer it as a kit - harness connector, etched PCB, parts, heatsink and a plastic case for $40. (Or whatever it costs and a bit of profit.)

Even though it's lossy to drop the motor speed with a series resistor pack, Toyota does it that way from the KISS principle. It works, it's reliable, and it's cheap. They can get rid of a little heat easily enough.

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A simple voltage regulator just replaces the series resistor with a transistor that drops the voltage to the load as needed. Still produces the same heat loss in that type of application. A PWM (Pulse Width Modulation) controlled would greatly reduce the heat and power loss.

Yes, I imagine those coils on the blower resistor mush get very hot in operation. They appear to be made of nichrome wire and they put them into the air flow inside the duct work to cool them. If you hold a regular 50W wire wound resistor up next to the blower resistor, the difference in size is very noticable. A wire wound resistor is about 1" in. dia. and 4-5 inches long. I know VW uses that style on some of their vehicles and the small nichrome type on others. The large resistors last forever, the small ones burn out just like the ones Toyota uses.

Yes, the resistors are made with nickel-chrome wire. The failure mechanism was due to metal evaporation due to the wire high temperature. The wire cross-section slowly decreased in time to the point to cause the failure. Rudy

There was a somewhat related thread in the rec.metalworking ng about some guys that have used brass or copper crimps and a bit more stainless or nichrome wire to jump the gap in clothes dryer heating elements- might not make a difference in their app but would the increased wire decrease the motor operating rpm? Pat

Yes, it does if all the rest (lenght, material, etc.) is kept constant. The electric resistence of a conductor is inversely proportional to its cross-section, therefore by decreasing the cross-section, the electrical resistance increases thus reducing the speed of a DC-motor. Rudy

I read too fast in my previous post. The statement was correct but it didn't answer your question. Nevertheless, the answer is still yes, because the resistance is proportional to the lenght. Rudy

Snips...

Heck, back in my day, B/W flybacks were 15,750(cps) and color ones were

I guess inflation hits everything... :>))

In my day, frequency was still listed as "cycles per second," much more descriptive, in my opinion, than Hertz, although I hear they read out the same on a freq counter... :>))