heater controller circuit again
 

A while back there was the thread on how to bypass the reed switch in the heater controller to get the footwells to work. In that thread several questions were raised as to how the actual circuit works. I don't know why but I am curious about why so much circuit is needed to just start a couple of fans. Questions are
How does speed effect the operation
How does engine temp effect operation
And what does the potentiometer control.
I am not an electical engineer but if anyone with the know how cares to look at the circuit I have tried to trace the circuit and place indications of the different components. So if anyone is interested here it is. I email the CAD version to anyone who wants it.


http://forums.pelicanparts.com/uploa...1167705279.jpg

http://forums.pelicanparts.com/uploa...1136512289.jpg

http://forums.pelicanparts.com/uploa...1136512364.jpg

http://forums.pelicanparts.com/uploa...1136407889.jpg

http://forums.pelicanparts.com/uploa...1136045311.jpg

Any better, sharper pics available? 800 pixels wide would be optimum. The component side of the circuit boards should be in focus on the resistors and diodes so the color codes are clear and sharp.

The pic of the trace side of the large board is reversed ... the image below is correct, since the numbers are legible:

http://forums.pelicanparts.com/uploa...1167729197.jpg

The engine compartment controller is a mix of technology..old school relays and reed switches and some primative logic circuits. The speedometer connection is part of the simple logic that requires two statements to be true. It goes like this:
If the engine is at set temperature [determined by the temp sensor on the breather]
and..If the car is not moving [determined by the lack of a speedo pulse]
Then turn on the engine fan.
In the above scenerio the footwell blowers do not turn on..so another logic circuit is required and needs to be smart enough to know that even though the rear blower is spinning this is not a call for heat!
The trim pot in the upper corner is a mystery to me. I've never traced its connections to see just what part of the controller it is tweeking.

Thanks for the replys.
The pictures are just the ones from the original posts. I don't think my camera would take anything better.
I flipped the board on purpose so the traces were the same as the picture. I thought it would make it easier for someone to trace the circuit.
Again if anyone wants the autocad drawing PM me with your email and I will send the file of the traces.
I guess my real curiosity was what the purpose of the pot was and if the jumper effects any of the logic sequence. I don't think it was ever really determined why they used what appears to be complicated reed switch circuit just to control the footwell blowers. The thought was that if the footwells didn't come on unless there was adequate current to the rear blower you would notice the rear blower wasn't working.
I was also curious why some systems seem to work with the replacement motors and some don't. I got lucky and did not have to perform the jump to make my grainger motor function. My thought was that if someone understood the circuit then the reasoning behind it would become more evident.
Maybe we should just let sleeping dogs alone.

can you read any numbers off the two transistors on the main board and the three surface mount transistors? just want to see if they are npn or pnp

If I have to I will unsolder and remove each component. It is at home now will pick up later this morning and take a look.

No! Don't do that, I think I can figure it out. I can almost see the SOT ones in the photos.

Higher res scans.

http://forums.pelicanparts.com/uploa...1167870672.jpg

http://forums.pelicanparts.com/uploa...1167870690.jpg