AC Panel Knob Wiring Diagram

[muwaha]

Hi All,

So I have a 1991 Ford Ranger 3.0 V6 2WD and I am trying to improvise on the AC Control Knob.
The knob itself (that turns the blower on) is basically crumbling into pieces.
I figure I just do a little upgrade to a 4 port switch.
The issue is this though, I have a wire that goes into this knob that is Blue/White and this wire is not showing on any of the diagrams (Google or my Chilton Manual), but for the blower to engage on the settings (Low, Med, High) this blue/white wire has to be crossed with the wires that do the knob settings (orange/black, red/yellow, etc).

Is there anyone that is a tad more familiar with the wiring and could help me investigate where this blue/white comes from?
I thought of running a hot wire straight from the batter, but I'm that would cause damage, seeing that when the key is in the "On" position, the blue/white wire kicks to ~1.2mv, while the other wires (black/orange, red/yellow) kick to 12V.
The picture attach is how my unit should look.. The knob itself is what breaking. The rest of the unit is fine.

 

[franklin2]

I don't see that wire color in the diagram below either. But the diagrams below can be off. I will say you need to think differently about how this circuit works. The motor is fed 12v anytime the key is in run, whether you select the switch or not. The switch and the resistors ground the other side of the blower motor. So on high, the switch fully grounds the other side of the motor to make it run at high speed. Any other speed, the motor is grounded through one of the resistors.

I would look at the diagram below, and verify all the wire colors on the resistor. There should be 4 different colors. If you are missing one of the diagram colors on the resistor, and instead have the blue/white there, you can assume that you can substitute the missing color on the diagram with blue/white.

 

[muwaha]

That's the exact diagram in my Chilton Manual, and as far as I can tell, I have all those wires plus the blue/white..
I'm thinking of just tracing the wire in the dash and see where it goes.
I've never actually had to trace a wire before in a vehicle before.
Have you done it? and if so, got any tips for someone just starting?

 

[muwaha]

I actually figured it out lol.
If it counts, I have a multimeter that dings on continuity, so as long as it's the same piece or wire (even if it's spliced) it would ding to let me know that it's somehow connected.
I traced the wire through my firewall and seen a faded blue/white cable attached to the ground on the driver's side under the hood between my brake booster and radiator resoviuor.
I took my multimeter, and it says it's the same piece of wire. So I'm assuming it's a ground wire, even though the diagram doesn't reflect a blue/white wire acting as ground.

So now my concern becomes should a ground wire have voltage in a car? When I take my multimeter black wire and plug it into the Cigarette Burner's ground, and the red wire off the multimeter to the blue/white wire, I get around ~1.2 mv.

 

[franklin2]

I don't like using the ding feature of the multimeters. Put your meter on ohms, and then take that reading again. I bet you do not get zero ohms.

 

[muwaha]

Hey sorry for the long wait.
Actually I did get 0 ohms.
I also just found the blower resistor so I'm replacing that too since I'm thinking that is bad.
I connected my blower straight to the battery and it works fine (which it should as it's brand new), but when I attempted to cross the wires where the knob is, it barely engaged regardless of it being the low, med, high setting.

 

[RonD]

The light blue wire is for the light bulb, illumination , controlled by main light switch and Dimmer

As you may have discovered the Blower gets 12volts with key on
The Fan Speed control is the GROUND for blower motor

High speed is a direct ground by-passing Resistor block
Lower speeds run thru resistor blocks 3 resistors, which lowers the ground connection, which lowers the voltage at the blower

Its DC power so there is no 12volts unless there is also 0 volts(ground) if you raise the resistance on the 12volt side OR the 0volt side it has the same effect, voltage thru the circuit drops
Most car makers uses the 0volt side because its safer, if a 12volt wire shorts you get sparks, blown fuse and melted wires, lol
If a ground wire shorts, in this case, all you get is a blower that won't shut off(with key on) because it has a full time ground short, no sparks, no blown fuse and no melted wires

 

[muwaha]

Thank you for that explanation. Now it's a matter of me figuring out which wire is which.
I replaced the blower resistor today but I still barely get any air through the vent regardless of which wire I use. With the knob having a circuit board with a resistor, I wonder if that ties into the entire circuit.
Honestly, since I confirmed that the blower works directly off the battery, I was thinking of just running wires to the cab with an on/off rocker switch and just use that..
I can't seem to find a replacement knob with the electrical connector (my AC Control Panel part number is E97H-19C925-AC. it's similar to the F97H series, but I don't need to replace the whole unit (the warm/cold, floor, defrost, etc), I just need the knob itself.

 

[dvdswan]

Don't forget that you push the button to turn on the AC too.

 

[RonD]

Should be an Orange/black wire on control, that's the HIGH speed direct ground that can go to pin 4 on resistor block, where there is another Orange/black wire that runs to the Blower, so 2 wires on that pin

Yellow/red wire is "med high" just below high, it runs to pin 3 on resistor block
Light green/white is "med low" to pin 1
Red/orange is "Low" to pin 2
For 4 speed


The Vent controls, Defrost, panel, floor, are done by a cable and slider, if direction doesn't change then its a cable issue
Temp control is also cable operated it opens and close a door ion the cab that routes air THRU the heater core(HOT), or around the heater core(cold)

Fan air flow has to pass thru the Evaporator on AC equipped models, evaporator can get clogged up with debris
Take blower motor off again and reach inside to the right(facing heater box) and you can feel the evaporator grill, make sure is clean
Evaporator can also FREEZE up when using AC if the "freon" get low, this also blocks air flow from fan

 

[muwaha]

dvdswan, That is my next portion.

RonD
Right now I just want the blower to work, but for some reason the HIGH (orange/black wire) doesn't give the blower enough force. I can barely feel it coming through the vent (defrost, floor, panel, etc).
If I connect the blower straight to the battery, I truly get the "high" setting that it's suppose to be.
When I cross the wires for Med High, It's, again, just pushing enough to barely feel it in the vents (as in I have to put my hand in the vent to really feel it).
Same with Med Low, and Low.

I'm sure I said this already, but I replaced the Blower Resister (after spending 3 weeks finding it in my truck) yesterday, but still the same result. Is there something else I should look at electrical wise?

I cleaned the evaporator out yesterday I took a small shop vac and got all the debri out before putting the new blower resistor in.
As for the AC, this does have AC, but the previous owner ripped it out and bypass (what I call) the serpentine belt from the AC Compressor.
I think she had the AC lines, and something else, but I can't remember the name. It littler connects to the evaporate..
The part is circular and between the evaporator and condenser.. I was told the name of it yesterday but forgot.
Once I get those installed, as well as get a belt to run with the compressor again, I plan on getting AC (provided I can find the parts.. It's sarces looking for parts for a 91 in my area. I have 8 junkyards but barely any parts for my year)

 

[RobbieD]

Look closely at connectors, terminals and wires, at both the blower switch and at the resistor block. I've seen these get overheated, and age, enough to deteriorate the electrical connections to the point where the blower just ain't getting the current it needs. Look for brown-stained or melted connector bodies, brown or green looking terminals (and obvious arcing marks), and signs of the wire's insulation getting too hot. Replacement pig-tail connectors used to be available for both ends, as this was fairly common.

 

[muwaha]

I'll check the resistor block pigtail.
Right now I'm fighting the electrical issue with the driver's rear brake light lol (seperate thread btw)
I was wondering why Auto Stores were selling the pigtail connectors lol. that makes sense.
I took a multimeter and all the wires are getting their ~12V (with the key on obviously), but I don't know what the resistance is suppose to be on them so I'm not sure what is consider "good".

 

[RobbieD]

Usually just a visual inspection will find suspect connectors.

I'll try to get a schematic for you for your other post in a little bit.

 

[RonD]

If you do not get full speed from the blower then either the 12volt wire, Brown/orange or the Ground wire, Orange/black is bad/corroded

You said the blower has high speed when hooked to the battery
So do that again BUT.....................only use 1 terminal on the battery at a time

With key ON
Use a jumper wire from Negative battery terminal to Orange/black wire, if you get Full Speed then ground for orange/black wire in the cab is not good

Key OFF, fan speed selector on High
Use jumper wire from Battery Positive to Brown/orange wire, if you get Full Speed then Fuse 9(30amp) in cab fuse box or its wiring is bad, doesn't have full 12volts

You can do the same with volt meter but................if its corrosion then the volt meter has a low amp draw so you may see full 12v but not when fan is running, 15amp draw
So test voltage at the fan while its running