HVAC blower motor resistor replacement

My blower motor has been working only on the highest setting for a while now. Finally getting around to replacing it. It was not an easy job for me, my hands just dont have the dexterity they used to after surgery on both hands. I have almost everything back in except for the top screw on the resistor (not sure how I'm going to get that screw started). Before more wiggling and cussing I decided to check the blower at this point. It works on settings 3 and 4 but not 1 or 2. Any ideas? Bad new resistor? Is there a way to check them? The old one does not show any signs of overheating or melting.
 
My blower motor has been working only on the highest setting for a while now. Finally getting around to replacing it. It was not an easy job for me, my hands just dont have the dexterity they used to after surgery on both hands. I have almost everything back in except for the top screw on the resistor (not sure how I'm going to get that screw started). Before more wiggling and cussing I decided to check the blower at this point. It works on settings 3 and 4 but not 1 or 2. Any ideas? Bad new resistor? Is there a way to check them? The old one does not show any signs of overheating or melting.
There's the possibility that your fan switch and or wiring to the switch is bad. When I replaced my blower motor and blower resistor I ended up having to replace the fan switch and the plug ins to the resistor and switch.
 
My blower motor has been working only on the highest setting for a while now. Finally getting around to replacing it. It was not an easy job for me, my hands just dont have the dexterity they used to after surgery on both hands. I have almost everything back in except for the top screw on the resistor (not sure how I'm going to get that screw started). Before more wiggling and cussing I decided to check the blower at this point. It works on settings 3 and 4 but not 1 or 2. Any ideas? Bad new resistor? Is there a way to check them? The old one does not show any signs of overheating or melting.


Not my Jeep but my Honda Fit had the problem with the fan only working on high. At first I replaced the resistor (HUGE pain in the ass) and it worked fine for about a week. Then, same problem. Internet research led to the problem being the motor wearing out (fan bearing) and - no expert here - overloading the resistor. So I replaced both the motor and resistor and have had no issue since (it's been almost a year). If you did the same and replaced both and you're still having problems my inexperienced and unmechanical self would probably think the resistor is not good - perhaps a crap brand or something.
 
HAHAHHA. This post cracked me up just now. Lol. I’ve had my new resistor hiding somewhere in my Jeep for a whole year now because I don’t feel like squeezing underneath the glovebox area lol been dealing with only the high setting for a year....I may do it tomorrow though after reading this thread
 
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HAHAHHA. This post cracked me up just now. Lol. I’ve had my new resistor hiding somewhere in my Jeep for a whole year now because I don’t feel like squeezing underneath the glovebox area lol been dealing with only the high setting for a year....I may do it tomorrow though after reading this thread
It sucked and I still dont have speeds 1 and 2!
 
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Have you pulled the switch cluster out of the dash and looked at the wiring and back of the switch yet?
That will be tomorrow, ran out of time tonight. So far everything I have ever worked on in my TJ has been in fantastic shape. Yes, it is 15 years old but the POs never messed with anything, it has only 60,000 miles on it, it has been in FL the whole time and garaged most of the time. I will be looking at that but I dont expect to find anything wrong there.
 
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My switch was slightly melted for a couple years before it acted up. It may have been like that before I got it. The first time I took the switch panel out after getting it, I noticed the melting, then it was a couple years later before it acted up.
 
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That will be tomorrow, ran out of time tonight. So far everything I have ever worked on in my TJ has been in fantastic shape. Yes, it is 15 years old but the POs never messed with anything, it has only 60,000 miles on it, it has been in FL the whole time and garaged most of the time. I will be looking at that but I dont expect to find anything wrong there.
Did you ever figure out what your problem was?
 
I have yet to personally see one of these resistor packs that keep burning up - the dealership that sold me my TJ changed it out and tossed the bad one. With that said, has anyone thought about rebuilding one with higher wattage resistors? Is it reasonably possible?
 
.... has anyone thought about rebuilding one with higher wattage resistors? Is it reasonably possible?
The problem with adding more resistance is, the wires are barely adequate for the original resistor and fan motor. In many cases the wiring and switches also suffer from high current draw.
 
The problem with adding more resistance is, the wires are barely adequate for the original resistor and fan motor. In many cases the wiring and switches also suffer from high current draw.
That's not what I'm saying...

You use the same value resistors as stock - just higher wattage rating that won't burn out. Don't know if its feasible as I've never seen the actual part.
 
That's not what I'm saying...

You use the same value resistors as stock - just higher wattage rating that won't burn out. Don't know if its feasible as I've never seen the actual part.
The resistor pack is the weakest link. If you upgrade the resistors to keep them from burning out the nest weakest link will burn up. I would rather burn out a resistor pack than have a dash fire...

There are 2 different types of resistors,
The old design, coil type
1590441789428.png


And the newer design, solid state.
1590441851544.png


The best way to avoid all of it is to fix the problem in the first place. Which tends to be a blower motor that is pulling too much amperage and causing everything to heat up to the point resistance also increases and something finally gives...
 
I have yet to personally see one of these resistor packs that keep burning up - the dealership that sold me my TJ changed it out and tossed the bad one. With that said, has anyone thought about rebuilding one with higher wattage resistors? Is it reasonably possible?
Here are some pictures of mine which is bad according to the missing low fan speed and my multimeter:
IMG_20200709_171000.jpg

IMG_20200709_171019.jpg

IMG_20200709_171028.jpg


Visually it looks fine to me. I was expecting to see some charring or delaminated PCB traces or something. All I see is the pitted and bubbly conformal coating. But the pits and bubbles aren't concentrated over just the low speed resistor trace so I'm not sure if that's related to it going bad. Maybe it has pinholes that let moisture in over time?

I dunno. All I know is my low fan speed doesn't work and my multimeter says that trace has ~15 Megaohms of resistance (versus the <5 Ohms for each of the others).

To answer your question though it would be difficult to solder anything onto this module. Maybe some sulfuric acid would soften the coating and expose some metal. But even once that's done I'd have a hard time fitting any kind of high wattage resistors onto this package.

I think the fan going full bore is roughly 10A. Of course fully on bypasses the resistor block altogether so the Medium-High speed is what passes the most current through the resistor block. So let's say the fan draws 8A on Medium-High. If I did my math right that means the Medium-High resistor would be 0.3 Ohms (which sounds sort of close to what I remember my multimeter saying). P=R*I^2=0.3*8*8=19.2W. So this little resistor block needs to make ~20W of heat on Medium-High.

I think it comes down to what kind of resistors would you use? With that kind of power in this small of a package I think the as-designed PCB traces are pretty cost effective. Yes they do make high power resistors but they're big and way more expensive than the PCB traces that are going to have to be there anyway.

The best design I can think of is a PWM circuit. That could definitely fit into this small of a package. And it would make negligible heat--it'd be way more efficient than just bleeding off power as heat. But our Jeeps don't give the resistor block a dedicated ground and in this case a PWM circuit needs a dedicated ground because it's driving an inductive load (there needs to be a flyback diode). Although maybe the flyback diode could be inserted elsewhere in the loop. But a PWM circuit will always cost more than some simple PCB traces. To say nothing of certain people's aversion (I'm looking at YOU haha) to that kind of stuff.
 
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Hmmm, yea a PWM circuit might make some sense - I'll noodle on that next time mine dies and I have something to look at. A FET, a couple of diodes, and a 555 timer IC might do the trick.
 
Hmmm, yea a PWM circuit might make some sense - I'll noodle on that next time mine dies and I have something to look at. A FET, a couple of diodes, and a 555 timer IC might do the trick.
A complicating factor is how our Jeeps are wired. You get 12V selectively applied to one of three wires and are expected to pass varying currents out the fourth wire. To power any kind of MCU or IC and be able to distinguish which wire has 12V applied you'll have to remember not to let any of those inputs back feed the others. Otherwise the inputs will be indistinguishable.

It would be lots easier with the addition of dedicated 12V and dedicated ground wires.

You'll also have to remember that the PWM frequency shouldn't be audible. That would be really annoying haha.
 
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A complicating factor is how our Jeeps are wired. You get 12V selectively applied to one of three wires and are expected to pass varying currents out the fourth wire. To power any kind of MCU or IC and be able to distinguish which wire has 12V applied you'll have to remember not to let any of those inputs back feed the others. Otherwise the inputs will be indistinguishable.

It would be lots easier with the addition of dedicated 12V and dedicated ground wires.

You'll also have to remember that the PWM frequency shouldn't be audible. That would be really annoying haha.
Keeping in mind that I'm just shooting from the hip here and haven't researched or thought this through, one "might" be able to use either diode logic or CMOS logic chips to alter an RC time constant on a 555 timer. Or if you wanna get fancy, run a crystal ocillator into a divide by N counter and enable the desired output with the switch signal - or something like that. That output goes to a pass FET, or maybe even just a good ol' power NPN to drive the motor. About 1KHZ would be really nice to preclude any passengers from ever riding in the Jeep! ;)
 
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