On the first 3 settings you get a little air, and on max you get max air. I bought a new blower motor resistor and installed it, and it didn't change anything. What else could it be?

 

This is the OP, I got logged out and lost my password

So I did some more reading and people say the plug could be the issue, with rust and corrosion. I checked the terminals of the old resistor and 2 of them were very rusty. So I pulled the plug off, and noticed that the wires were wrapping in electrical tape. I undid the tape and it turns out the plug had already been replaced and they just hand twisted the wires together and taped it. Nice

So I wire nutted the wires tightly just to make sure it would work before I soldered it all up, and it still didn't work. I took the plug off again, cleaned the connections with IPA and Deoxit, plugged it back in, still no dice. I am assuming at this point the corrosion might have ruined the connector internally, so I ordered a new connector off Amazon. It will be here tomorrow, I will wire nut that up and test it and it if works I will properly solder and heat shrink the connections.

If a new resistor and a new connector don't fix it, what else could it be?

 

Blower motors get 12volts directly(key on)

Fan "speed" is done via Ground connection

Max speed is a direct ground from the cab, by-passes resistor block

So if you have Max speed but no lower speeds then its either the resistor block OR the Fan switch

You don't mention the YEAR of the Ranger, always good to include that with questions
But all years basically work the same way
1994 diagram below

Fan gets 12v from the fuse(9)
All speed settings are from Cab Ground(G200)
As seen HIGH bypasses resistor block

Other speeds Ground thru 1, 2 or 3 resistors in series, 3 resistors is highest resistance so lowest speed, as seen

You can check the resistor block connector wires with OHM Meter, all should be 0 ohms to ground when that speed is selected in cab
If not then switch is the issue

 

Thanks for the schematic, odd they would use "Brown/Orange" as the hot wire vs red, that would have taken me a while to figure out :)

I am leaning towards the contacts in the plug being the issue since it had been replaced before and two of the terminals on the old resistor were heavily rusted, and if they are rusted, the contacts on that plug are rusted too. I am going to replace the plug when that shows up, and if that doesn't help I will Ohms test the wires when it is set to the various modes and see if it is a switch issue. But honestly, if I replace the resistor block, and replace the plug, and it still doesn't work, looking at the schematic I don't see what else it could be except the switch at that point.


Edit: 2002 Ranger

 

2002 wiring diagram below

Pretty much the same as most Fords

Yes, the connector and wires on the Resistor assembly must be able to pass up to 40amps(fuse rating) same as the Positive wires for the motor
People often think only the positive side needs to carry the high Amps, not so, negative(ground) must carry the exact same Amps for the circuit to work as designed
If corroded or damaged connection(ground or positive) can only pass 5 amps then no motor

 

So I swapped the plug out. Here is what is happening. I will put a number between 1 and 5 indicate how much air is blowing

• On the first setting, I get a little bit of air coming out (1)
• On the second setting, it kinda feels like a TINY little bit more air is coming out (1.25 - 1.5)
• On the third setting, it feel unchanged from the second setting (1.25 - 1.5)
• On the max setting, it blows like you would expect, MUCH more than the previous settings (5)

So since at least some air is coming out on all settings, I know none of the coils on the resistor are broken or the circuit would not complete. I would think if one of the stops on the switch was broken, again the circuit would be broken when that setting is selected, but at least some air is coming out, so the blower motor is getting power, which means power is getting thorough the resistor block and getting to the motor. But the resistance does not seem correct. This is the part I purchased and it looks the exact same as the one I took out of the truck. I can Ohm test the wires to ground, but again thats just going to show me what the resistance is and confirm that the circuit is complete, but I already know that cause the motor is getting power. Should I measure DC volts on the orange/black wire as I switch through the settings to see if there is a difference in how much power is getting to the motor?

Unless this is how it should work? I never owned a Ranger before, are the second and third fan settings supposed to be very weak and very similar and way weaker than max?

Edit: Looking at the schematic, if the Med - Lo and Med - Hi wires were shorting to ground, they would act just like the Low setting, right? If that's the case, I guess they could be shorting to ground in the switch itself, and if that were happening, if I am reading the schematic correctly, settings 1, 2, and 3 would ALL be Low, and Max would be Max, which is how it feels. I'm going to replace the switch (its showing up tomm) and see if that fixs it, if not I will measure DC power as I cycle through the settings and if they are unchanged then that would seem to indicate it is shorting to ground somewhere along the wire run?

 

If you look at the 2002 diagram you will see the Resistor Block(bottom right) has its own Ground wire(G105) which is for Low Speed, there is no OFF setting on speed switch
Low is not a setting just a position of the ****
So Fan is always grounded, in Low Speed, with key on, other speeds just change the resistance, but none cut the ground, i.e. no OFF

Med. low and med. high, do have wires that go to resistor block, so they Ground those resistors from Cab ground(G201)
High by-passes the resistor block and uses G201 so you know that's good

And since you have Low you know G105 is good as well

There is a big difference from low to med. low, and from med. low to med. high, as far as air flow, no guessing needed

Get an OHM Meter and unplug the resistor connector and test the two wires for med. low and med. high, should see 0 OHMs on that wire when is selected in the cab


1995 and up Fan OFF is done by the Mode/Vent switch, when its in the OFF position 12volts to fan is cut, that's the only OFF for the blower fan, just FYI

 

So if Med Hi and Med Low were shorting to G201 (inside the switch possibly), they would act like Low speed, right?

And just to make sure I am visualizing this correctly, the black wire I connected to the resistor from the wiring loom under the hood, that's G105, and G201 will be a different ground wire back in the dash behind the HVAC controls, correct?

I will be doing that tomm and I'm going to pop the bezel and radio out and take a look at the wiring to the switch. The replacement plug that was there was connected to the car by hand twisting the wires together and wrapping it in electrical tape, so it seems the previous owner had some ... interesting ideas on how to wire things. For all I know he could have wired the Med Hi and Med Lo switches to G201, which would short them to ground before they got to the resistor and make them Low mode. Or the wires/connectors could be broken I guess, you make a good point, since power is controlled by the vent selector, the fan speed selector can't kill power to the blower, so if Med Lo and Med Hi aren't doing anything due to being cut/damaged/corroded/whatever and just aren't making any contact with anything at all, the fan would still work, and they would just function as a Low setting. The Ohm test will tell me that, or maybe it will be visually obvious once I take a peek.

 

When key is on and Mode/Vent switch is in any position except OFF, the blower motor gets 12volts

The resistor block is always Grounded by its black wire(G105), but thru 3 resistors, which would be Low speed
If the speed **** in the dash was set to med. low then resistor block has a NEW ground path and only thru 2 resistors, so higher fan speed than Low, NEW ground path uses G201 in the cab
Med. high changes to NEW ground path thru 1 resistor, so even higher speed, also use G201

High speed by-passes the resistor block entirely, no resistors, it's a direct ground for blower motor, via G201

So if low, med. low, and med. high all seem to be the same speed, then med. low and med. high wires, or switch contacts, are not giving a NEW ground path in resistor block

Medium low setting
12v-----------blower motor-----------------resistor-----resistor----------------------------------med. low(cab switch)---------------G105(cab ground)

 

So I took readings. Under the hood, the wires coming from the cab were reading around 40 kOhm's when the respective setting was selected inside the cab. So that is wrong since you said it should be 0 Ohms. On thing though, I tested to the body of the truck, should I be testing to the black wire in the wire loom instead?

So I popped the radio and the bezel off, and took out the switch. I opened the switch up and there was a good bit of dirt mixed in with the grease they have in there, so I thought maybe it was dirty contacts. So I cleaned it all up, reassembled the switch, and tested for continuity between the various modes. And continuity showed the various contacts connecting to what they should be connecting to.

I plug the switch back in to the truck and ... no change. First three setting are all low, and then max. I visually inspected the wires and did not see any cuts, breaks, or things that would cause a short.

If I manually shorted (using jumper tweezers) between the power line coming into the switch in the cab (orange/black), and the terminal for the med-lo or med-hi settings, that should make the fan run at those speeds, right?

I get that, but if the switch is good, what else could be wrong?

 

Ok, this official makes zero sense. New switch came in, and no change. So I hav changd the Resistor Block, the plug going to the resistor block, and the switch, and it did absolutly nothing.

None of the resistance measurements make any sense. I don't know which ground to use, I think I was using a proper engine ground (I got continuity between the black wire and that spot on the engine) and when on low, I was getting 2-3 Ohms resistance. Which according to RonD is wrong. I switched to the yellow green wire and did the same thing, but I forget what result I got. I know at some point I got 0 Ohms where I shouldn't have because I wasn't on the corresponding wire to the fan setting it was on.

Regardless, there is nothing else to replace. So what now?

 

Yes, you could use the black wire(G105) on the resistor block connector as the Ground to test OHMs from the switch wires(G201), so OHMs between 2 grounds should be 0
0 ohms is what you should see, use lowest OHM setting on meter
Continuity only means wire is not broken, could have high OHMs


No sure of exact ohm rating on the resistors in the block so this is just an example
If each resistor in the block is 100 ohms then Low speed has 300 ohms resistance. 3 resistors
Med. low would have 200 ohms resistance
Med. high would have 100 ohms resistance
High, 0 ohms, no resistance

If med. low and med high wires themselves had 400ohms resistance then Ground path would stay with the Black wire, low speed, with 300 ohm resistance
Electricity always travels the path of least resistance

 

Well I didn't do that :)

I put my meter on continuity and put one probe on the Yellow/Red (Med Hi) wire that runs to the cab switch, and started poking around the engine bay until I heard a beep, figuring that would be a ground connection. I got a nice solid beep off the alternator housing so used that as a ground.

I started the truck up, and put the blower on Low. It blew on low. I then grounded the yellow/red wire from the cab switch to the alternator housing. Nothing happened. Although now that I think about it, shouldn't I have grounded the yellow/red wire going to the resistor block instead?

For that Ohm test, could you be very specific on what connections to test? Is this correct (Using your "100 Ohms per resistor" assumption)

Black wire connecting to cab switch < - > Black wire connecting to resistor = should be 0 Ohms
Black wire connecting to cab switch < - > Med-Lo wire connection to resistor = 100 Ohms if fan is not set to Med Low, 0 Ohms if fan is set to Med Lo
Black wire connecting to cab switch < - > Med-Hi wire connection to resistor = 200 Ohms if fan is not set to Med Hi, 0 Ohms if fan is set to Med Hi

Is that the right test? Also, given tat I have replaced the resistor block, plug, AND switch, why would it still be failing? Would it be most likely I just got a bum resistor block sent to me?

 

And just to level set what is known, the only things in the circuit are power, the resistors, and 2 ground points, G105 and G201.

• The blower motor is getting power, so I know the fuse and relay are working, or the fan wouldn't spin
• I know the blower blows on MAX, so I know the G201 ground point is good, because on Max, the power just goes right to that, and it works.
• I know the blower blows on Low, so I know the G105 ground point is good, and I know all three resistors are in place, because on Low, the power goes through all 3 resistors and goes to G105 and blows low.

Med Hi and Med Lo simply take the circuit from their respective resistor terminal and bring it to G201 instead of G105. And we know G201 is good. So the ONLY thing that could be causing the current behavior is a break in the circuit between the Med Hi and Med Lo terminals on the resistor block, and G201, right? If I am understanding this correctly, if that connection was broken the circuit ground would be G105, which is Low, which is why Med Lo and Med Hi both act like Low

But literally ever connection in the circuit is brand new. New switch, new plug, new resistor block, so where could it be broken?

 

New just means NEVER EVER tested, not "tested and works", so grain of salt on ALL "new" parts

You test resistor block Connector, while it is unplugged, key off
Set OHM Meter to 200 or its lowest setting
Touch the two meter probes together, should see 0 ohms(direct connection), this tests if the meter is working correctly

Put 1 probe on black wire(on connector)
1 Probe on the wire being tested, i.e. med. low or med. high, switch in the cab needs to be on matching setting
Should see 0 ohms
A direct connection between the two ground points thru the speed switch

Yes, both ground points are working or you wouldn't have both Low speed and High speed

 

If I put the cab setting on low, then go under the hood, and connect the Yellow wire to the Black wire on the resistor block, it should switch to Med Hi, right? And if it does that, that proves the resistor block and resistor plug are working fine, and the issue is somewhere before that, which would be the switch in the cab, or somewhere along the wire.

 

Yes, if you Ground the yellow(#3) wire then it would by pass the switch and fan speed should change to med. high

 

OK cool, that will tell me which "side" the issue is on, the resistor block side or the switch side. I'll do that test tomm and go from there.

 

The mystery continues

I turned on the truck, and put the fan on low. I touched the Yellow/Red wire to the black wire under the hood, and nothing changed. It kept blowing on Low. Then, with the ground under the hood still disconnected, I ran through the settings, and it STILL WAS RUNNING ON LOW. The ground wire coming off the resistor block was DISCONNECTED.

I turned everything off, and unplugged the connector from the resistor block I then took the plug from out of the cab switch, and checked continuity and resistance between all 4 connections. All four wires showed continuity and minimal resistance (1-2 Ohms). So there is no break between the wires going from the switch to the resistor block.

I happened to have a spare resistor block (it came with my new plug), so I swapped it out. No change, Low, Med Lo and Med Hi work as Low, Max works on Max.


So at this point we have a brand new switch, TWO brand new resistor blocks, a brand new resistor plug, continuity between all the wires, and confirmed power to the motor, and (supposedly) confirmed connection to both grounds. But it STILL doesn't work.

Is this beyond hope?

 

One thing I noticed when I was working on something totally unrelated is that there looks to be a broken ground strap, underneath the passenger side door underneath the truck. I see the terminals but the strap is torn. I wonder if that is related to G201, and if the only ground that is actually on place is G105, which is always Low?

 

According to the diagram Low speed would be off if resistor block ground was disconnected

Does blower motor run with resistor block unplugged?
It shouldn't
If it runs with resistor block unplugged then blower is getting a weak(high resistance) ground from somewhere else

Does HIGH work with resistor block unplugged?
It should, as it by-passes resistor block

 

I can try that.

If I grounded the yellow/red wire coming from the resistor block directly to the negative terminal of the battery, that should run the fan at Med/Hi, right?

Also, could a problem with the blower motor itself cause these issues?

 

Yes, a problem with blower motor could have those symptoms, long shot but not a no shot

Its a 12volt DC motor, so speed can be variable based on Voltage passing thru it
In this setup the negative side(ground) is used to restrict voltage passing thru the motor

So maybe your HIGH speed is NOT as high as it should be because of internal resistance in the motor itself

Unplug the 2 wire connector for blower motor
Put OHM meter on each wire going to the motor
Should see under 1 OHM, 0.5 ohm is expected

 

Cam you explain this in more detail? I am insure how it would work. Do I need to have the wires from the cab connected to the resistor block wires while I am doing this test?
Here is a picture of under the hood. 4 Wires coming from resistor block, 4 wires coming out of the wiring loom. Using the numbering below, which should I have connected? When I tested it, I had 4 & 8 connected, 3& 7 connected, and then 1 & 2 connected and the fan did NOT run in Med Hi mode. What wires do I test for 0 Ohms? If I disconnect the wires from the cab to test them they won't have any connection to the switch!

 

Do we know where the physical location of the G201 ground is on the truck?