The first Schematic show the factory wiring of the Air Conditioning blower motor. The Factory way varies the resistance to the ground inorder to change the speed of the fan. Doing it this way dose not allow the motor an easy path to ground becasue of the resistors when discharging static electricity after turning the engine off and the fan winds down. The way I plan on doing it is to vary the current going into the motor and provide a direct path to ground for the motor to discharge static electricity. The first Image is the factory way and the second one is my way

JMC

 

Why would you want to do that? You are going to build up a lot more heat in the resistor pack doing this.

 

So you are getting rid of the resistor pack and using a reostat to control the power side. Actually should work just fine. I read ( and posted) an article recently printed in the ASE "blue seal" tech news about ford having problems with coolant electrolysis. It mentioned that poor grounds can aggravate this problem. Mentioned specifically after market electronics not grounded properly. Seems that the better your ground connections the fewer problems you will have with electrolysis.

 

Sorry for the delay in the reply, just got off a plane from PIT.
For what my bleary eyes can see at the moment, I cannot see a functional problem with doing this.

I tried to track circuits 261, 754, 753, and 57 to see if they were used somewhere else without any luck, so it seems that they are contained to the blower motor resistor to function selector switch.
I looked through the section 54 in the EVTM and the splice index ( as I am sure you already did ).

Operationally, it is the same, no delta as to where the current drop is added ( on the power side of the motor or the ground side ) so speed wise and circuit wise it is the same = same.

I keep going over current drop in my mind, and cannot see a functional problem with your redesign. I-t and R-t are not changed in the Ohm's Law circuit creation, so without finding a re-use of the circuits from the selector switch or the circuits being changed, and no functional change to the selecotr switch itself, I'd have to say it is going to work 100% the same. Then again it is 1:20 am

Good luck, let us know how it turns out.

Steve

 

Pestco1,

I have had to change 3 heater cores in my truck since it was new. The problem is not just aftermarket electronics. In stock form the path of least resistance for grounding static discharge from the fan is from the fan motor to the heater core becasue of all those resistors that the charge has to overcome in the ground. My last core has a hole right smack in the middle of it from being zapped. This way the path from the motor to ground is the wire.

momalle1,

Why would there be more heat in the resistors?

JMC

 

Any load (resistance) is going to create heat, but mostly on the positive side of the circuit. I'm sure what you are doing will work, I was just curious why you would want to do it.

 

Momalle1,

When, and that is the Key, I do change the set up I will monitor the resistors for heat. Better safe than sorry.

JMC

 

Hey JMC... if you need some help with that, I'd certainly be willing to lend some of my automotive electrical expertise! Just let me know buddy.

 

Can I ask how that is ?

The selector switch, with the resistors, is a series circuit with the motor, which will cause a the voltage to drop, and the motor to run slower or faster, depending on the variable resistance ( speed selector ) added to the circuit.
This is Ohm's Law and Kirchhoff's Voltage Law.
The same current flows through each part of a series circuit. If the motor is capable of drawing 80% of the fused source then the Blower motor should not draw more then 32 AMPS, which means that the resistors, being on the pos side of the circuit in relation to the motor or on the neg side, either will have the same max of 32 Amps on it, but a different voltage level, in relationship to the resistance of the blower motor, depending on the speed selector setting.
Considering that high speed is 0 ohms added to the circuit, and 2.33 ohms is enough to make the motor run on low, it can't be that much resistance to the motor. So if 50% of the Resistance is somewhere between Med Lo and Med Hi speeds, the motor should have a resistance of about 0.475 ohms.
If anything, the most voltage drop over the selector switch is in the LO position, and this would cause the most heat build up in the resistors, as HI position seems to add 0 ohms to the circuit, and puts full voltage on the blower motor ( and the wire in the speed selector is just that, wire taking an estimated 32 AMPS ).
The Power used by each device in the circuit is calculated by P=V*I. So the circuit in total is 384 Watts, at MAX. The load at 80% of fused source might not hold true in Auto applications.

The resistors are not going to heat up any more or less by changing the orientation.
Keep in mind current flow is from NEG to POS in a DC circuit.

edit: boy I need to learn how to spell..

 

if static charge in the blower motor is the problem couldnt you run a ground from the blower motor to the body? or maybe your blower motor resistor isnt functioning properly and has to many ohms. have you ever changed the resistor?

i've seen very few vehicles that suffer from coolant electrolysis. but i did see this 1 crown vic squad car (that i didnt get to work on) that has had 3 heater coors put in. extra grounds ran for all their cop accessories and ford engineer even said to replace the engine. and it still came back in 14k for another heater core.

this is very interesting post and i cant wait to learn more.

 

It might be easier to run an extra wire from the Blower motor casing to ground. In all honesty I had not thought of that. Here is where I got the Idea;
From http://members.shaw.ca/autocheck/electrolosis.htm
JMC

 

That last post is right. The older models used a resistor in the positive side of the circuit. It fit into the blower box ( prob. to help keep it cool) The check for a blower malfunction was to check for power at the resistor, then pull it and check the windings for opens. I will be posting something about the resistor and your ground problems with ASE as they should have mentioned it in the service bulliten. If an aftermarket radio can cause a problem then the blower motor ( with all the amperage it draws) will surely be an issue. I think I will ground the blower body now while it is still fresh in my mind.

The other part of that bulliten I mentioned noted that you can also ground the heater core itself to help alleviate this problem.

 

Pestco1,

The same people who wrote the article that I qouted from do not recommend grounding the core.


JMC

 

I guess you need to find a way to ground the coolant and not the core.

 

I finally got around to doing this rewire. The fan seems to blow harder, move more air. Other than that every thing seems to be fine. I will now connect the heater core hoses that I had bypassed when I changed out the 8th core earlier this summer.

JMC